73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => 73-87 Chevy & GMC Trucks => Topic started by: philo_beddoe on December 18, 2015, 07:04:24 pm
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I know my setting is 8 degrees btdc, the manual states that as well as the decal on top of the rad support. But that is for a stock factory application.
How do you determine your timing when you make changes or modifications? Such as a different carb (different barrels) or the intake or even a different engine? What do you use as a reference?
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Whatever the truck wants and doesn't ping. I'm running 16* BTDC right now.
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Ok, because i have a 4 bbl qjet and a gm intake. Factory it came with a two bbl carb on my 305. I also recolect that a little advanced is better in regards of a little more power and better gas mileage.
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the more timing you can get generally the more HP. on our mud trucks most times right when the starter starts to have problems starting the engine is where we sit at. with open headers you cant hear the ping but its the rule of thumb we use and as long as we dont overheat (due to pre-detonation) we keep it there
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Read:
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwih98CGnujJAhXKWT4KHQ03ClsQFggdMAA&url=http%3A%2F%2Fwww.corvette-restoration.com%2Fresources%2Ftechnical_papers%2FEngine_Timing.pdf&usg=AFQjCNF9cOSbx-od28Z9Ww3ALWZX6fT-Ew
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also this
http://forum.73-87chevytrucks.com/smforum/index.php?topic=32085.0
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Think of your base setting as nothing more than a baseline setting. There are many variables when it comes to playing with timing, carburetor settings and finding a good mix for your driving needs and without any adverse effects. The old school method of advancing it until it pings and then backing it off is an easy way to see how much advance your engine can handle. Do this on a hot day with regular octane fuel in the tank. Then recheck your timing and record your settings. This will help you understand your particular engines timing spectrum so you can really dial it in.
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Ok, hear this...right now my engine seems stuttery, if i start it cold then turn it off, its hard to start it again, like im flooding it. Almost to a point where it feels vibrating or wobbling. The timing just feels off, please tell me this makes sense. The bulb on my timing light blew. Can i just slightly advance or retard till she smoothes out?
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That sounds like a choke issue not a timing issue
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Ok, i'll buy that. I'm not an expert on carbs and chokes, what can i do?
As a matter of fact, lately its been kind of tough to start up, really have to work the pedal to get it going when cold. After its fully warm, as long as i dont touch the gas pedal, it will start pretty quick like it should.
A while back i messed with the fast idle screw, could that be it??
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http://ericpetersautos.com/forum/showthread.php?6617-Some-useful-Quadrajet-tuning-tips
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Ok, thanks. I think Vile nailed it though!! Or i did something right by accident. I turned the fast idle screw in one full turn, then it started at the touch of the key, it took a couple minutes to kick down as it was in the 30's last night.
After the engine reached temp i tapped the pedal and it kicked down. I let it idle for a minute and turned it off, waited a few seconds then she started again at the touch of the key! Bam! And i did NOT put my foot on the pedal.
Here's the thing, i had that fast idle screw backed out to much from summer when i did not want it to idle fast at start up. And now thats it cold-cold, it chugged when starting. (before i adjusted the fast idle screw)
Question- under normal applications, basically a factory set-up, how should these engines idle at first start up, and how long until it should kick down to normal warm idle? Are we supposed to just sit there and wait until the idle drops before putting into gear and taking off? What if we dont have patience to sit and wait, what if we are late for work in the morning and need to just go and the engine is still racing?
Does this all make sense? Whats the purpose/function of that fast idle screw that sits under the choke? Thanks...
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Use a Vacuum gauge and set the timing to the highest reading at idle.
You will be very close.
If you like you can then advance it a little until it fuel knock or hard start (hot)
Then back up a degree or two.
Tom
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Ok, so whats a optimum reading. 22 ft. ?
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Philo,
Don't set your timing based on vacuum readings.
To answer your other questions, let's start with what carburetor you have?
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Rochester, qjet, M4ME
And it doesnt make sense to take off before the high idle kicks down, or else the drive shaft will clunk into gear. How did these trucks start in the morning when they were brand new, did the salesman at the dealership sit there and then punch the gas to kick it down when taking someone on a test ride? Or did he clunk it into gear right away while the engine was racing? Just saying...
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Rochester, qjet, M4ME
And it doesnt make sense to take off before the high idle kicks down, or else the drive shaft will clunk into gear. How did these trucks start in the morning when they were brand new, did the salesman at the dealership sit there and then punch the gas to kick it down when taking someone on a test ride? Or did he clunk it into gear right away while the engine was racing? Just saying...
If something clunks when shifting into gear you have a worn component somewhere.
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Only if the idle is a little high and only going into reverse, u-joint?
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If your choke break working?
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Yes it is, i believe. Here is a crazy question, how are you supposed to start a stock chevy engine? Here is what the manual says, is this right? Why do they tell you to NOT kick down from fast idle?
Will the idle go down automatically, can the choke be adjusted so the fast idle comes down sooner?
My idle wont come down unless i press pedal to floor and back up, contrary to what they say here under the first bullet.
I always forget and disobey the third bullet.
(http://images.tapatalk-cdn.com/15/12/22/5cc3b6952a46a6239c47b6a2b0625e37.jpg)
(http://images.tapatalk-cdn.com/15/12/22/ceff738f8126f19aaf6b171d01cf03fd.jpg)
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Hmmm...
The choke normally cannot pull the choke closed when the spring tension is on it. That is why it says to push slightly to let the pawl out so the choke can close. Pushing the footfeed down all the way does three things, it sets the pawl on the choke in the closed position (butterflies closed), sets the idle speed pawl into the high idle notch, and squirts raw gas into the intake. So, the carb is now set start with the choke blades nearly closed (never want them completely closed unless there is an included air bleed in the butterflies), the throttle blades are slightly opened, and there is raw fuel sitting in the floor of the intake (however, it is injected at a high speed/pressure so it vaporizes some too). This creates a rich fuel to air mixture to help the spark find the fuel better at very low intake air speeds. Too much fuel however and the spark is doused like a match under water.
Once the truck starts it runs at high idle (the high idle setting can be changed on most carbs like the way you did it). The engine should idle at the lowest high idle it can to remain running smoothly when it is cold or about 1200-1400 rpms (YMMV), this should not have to change for different seasons once it is set. (as an aside, I run my distributor power wire through an electric oil pressure switch so the truck will not start until the oil pressure is there, it will also shut down the engine if the oil pump stops working). After the engine has idled at this high speed for a few seconds or longer depending temps (it has to be warm enough on the piston tops to encourage further vaporization of the really cold incoming fuel, in addition, the intake manifold itself has to get warm for the same reason, if an air gap intake is being used with blocked off heat risers, cold starts will always be somewhat troublesome in really cold weather at normal air/fuel ratios), then knock it down to the next setting (if the carb has multiple idle speed settings) or to normal idle with another light push on the foot feed. Sometimes the choke will open and the idle speed will not come down or vice versa, then the carb needs some TLC. The linkage is binding from dirt, poor settings or the choke heater/vacuum lines are not working correctly.
My personal opinion about carbs is that they such simple mechanical devices they defy logic, yet they can cause the most intrepid of intelligent masculine men to go completely crazy trying to diagnose why they don't work right. Besides, a lot of 'carb troubles' aren't after all.
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If your choke is setup properly yes it will automatically kick down for you.. That is the whole point of the choke.
The choke is a timer and it can open slow or fast depending on weather. If you have it open to slow it will run in high idle for too long and if its too fast it will cause bogs when you try to drive it. Finding the happy medium depending on the truck and weather is the difficult part.
Some people choose to kick it down earlier so they can drive off.
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If your choke is setup properly yes it will automatically kick down for you.. That is the whole point of the choke.
The choke is a timer and it can open slow or fast depending on weather. If you have it open to slow it will run in high idle for too long and if its too fast it will cause bogs when you try to drive it. Finding the happy medium depending on the truck and weather is the difficult part.
Some people choose to kick it down earlier so they can drive off.
Must be a difference between Holley's and Rochesters. I stand corrected.
I knew Rochesters used vacuum to help release their chokes as well as a heater but never realized it was strong enough to pull it off high idle, guess I never paid much attention.
My Holley Truck Avenger has never self-released even when brand new, neither has any of the square bores I've used over the years. Of course they were all older style carbs using either a heat stove (from the exhaust inside the intake manifold) or an electric heater. Neither was adjustable for any particular weather conditions beyond how cold it is (meaning the colder it was the longer it took for the heat to start working on the bi-metal spring, although the heat -source- [12 volt electric in most modern cases] was constant no matter the temperature).
One thing not touched on is the heat riser proper. The tube from the heat stove around the exhaust manifold going to the stock air cleaner horn (haven't seen one in working condition in decades other than on a show truck). But these work good during warm up in really cold temps.
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If your choke is setup properly yes it will automatically kick down for you.. That is the whole point of the choke.
The choke is a timer and it can open slow or fast depending on weather. If you have it open to slow it will run in high idle for too long and if its too fast it will cause bogs when you try to drive it. Finding the happy medium depending on the truck and weather is the difficult part.
Some people choose to kick it down earlier so they can drive off.
I would like to operate just like a modern car, and that is...you start the engine, it runs at a slight high idle for up to about a minute and drops down nicely to the normal warm idle.
What do i adjust to get it to kick down easier and faster,,,wothout stomping on the pedal, if the manual says in 30 seconds slightly depress the pedal to kick down the idle.......then how do i do that?!!? I do appreciate the feedback. Thanks.
Yes, i would like to kick it down earlier, so i can drive off.
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If your choke is setup properly yes it will automatically kick down for you.. That is the whole point of the choke.
The choke is a timer and it can open slow or fast depending on weather. If you have it open to slow it will run in high idle for too long and if its too fast it will cause bogs when you try to drive it. Finding the happy medium depending on the truck and weather is the difficult part.
Some people choose to kick it down earlier so they can drive off.
I would like to operate just like a modern car, and that is...you start the engine, it runs at a slight high idle for up to about a minute and drops down nicely to the normal warm idle.
What do i adjust to get it to kick down easier and faster,,,wothout stomping on the pedal, if the manual says in 30 seconds slightly depress the pedal to kick down the idle.......then how do i do that?!!? I do appreciate the feedback. Thanks.
Yes, i would like to kick it down earlier, so i can drive off.
Adjust your choke dial. One way will be faster and the other is slower. Nothing carburated will ever function like fuel injection ever.
You technically shouldn't have to kick it down ever as that is what the choke will do for you but some people are impatient.
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i think the main difference between the way how these trucks run now and how they used to is the gas and mixtures we use now. idk what they were back then but it sure is different than now. my 79 would run one way one day and i would fill up and i would have to tune the carb again
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I set my choke to be on as little as I can get away with, coming off as quickly as I can get away with, without stalling or choking out.
I never let my vehicles warm up before driving away. I get it running, and I drive off. I am just super gentle until the engine warms up. It will warm up the fastest if it's driving.
I've owned more carbs than fuel injection. I am ~that~ old. Or cheap. Probably both.
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Electric choke on a carb will not kick down by itself.
Will always requires touch of the throttle to disengage the high idle cam from the throttle linkage after the choke spring heats up a bit and allows the high step cam to release.
Adjustments will depend on what your eng wants cold. Choke spring to tight takes to long to come off high idle, too quick and eng stumbles bogs or quits.
I don't wait either much more than less than a minute unless it really cold out. Watch a high idle on icy roads but if weather that bad let it warm up a little anyways if you can.
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Electric choke on a carb will not kick down by itself.
T
If it is working correctly the automatic choke should disengage the fast idle once the choke is opened.
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Is there an electric throttle kicker involved?
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Is there an electric throttle kicker involved?
Chokes have a stepped cam. When you trigger it the cam is on the highest level. As the choke opens the cam moves till the tab falls off and resumes normal idle.
If the choke remained on the high idle after opening it would be a crappy truck to drive.
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Ok, never seen a choke spring that could overcome the throttle return spring which is holding pressure on that stepped cam holding the high idle on a q jet until the throttle pressure on the cam is released.
Post 20
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I tend to agree with blazer, it doesnt seem to ever want to come down on its own, like a modern EFI does. All i want to do is tap the pedal between 30 seconds and one min. and have the idle drop nice and easy. How should i adjust the choke dial, lean or rich?
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Other than me trying to explain why an electric choke wont kick down by itself, here is a post that explaind how they work from the beginning. Note the word tickle is use towards the end of the post (Fast idle cam and Fast idle screw) http://www.chevelles.com/techref/Adjusting_Automatic_Chokes.htm
Carburated electric chokes will not drop off high idle or and other step of idle untill you touch (tickle the throttle) Note the factory manual pic in post 20 from the person with the original question asked basically say the same thing.
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philobeddoe: You need to get the proper documentation for adjusting the choke linkage from start to finish, Once your running a blip of the throttle should drop the fast idle down to the next setting or step thanks to choke pull off allowing the idle to come down some. It will never do it by itself, the choke flap will open but thats it.
If the choke never comes off and idle never comes down at all your chock coil is bad or you have no power to it.
Lot of info on the net for this.
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099#msg273099 date=1450919101]
Enaberif
Chokes have a stepped cam. When you trigger it the cam is on the highest level. As the choke opens the cam moves till the tab falls off and resumes normal idle.
As you stated you must trigger the cam.
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Well, what vile said makes simple sense too. A simple touch of pedal should disengage high idle. Mine does, but not quick enough. My carb is very clean, like new. No sticking issues.
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Woops, i was typing as posts 35 and 36 came in. Stand by...
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Then it's not totally adjusted correctly. The link I put in earlier explains the relationship between the fast idle, choke pull off and kickdown after start.
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Ok, as stated, my idle does drop down like it should, but not quick enough.
Got it, adjustment it is. First thing in the morning, i'll have a cold engine. I'll study that link and give it a try. Thanks.
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My original point from your question in post 20 is the electric choke is not totally automatic. It still requires driver input.
If you start up cold with the choke set to highest idle and don't touch anything, come back 30 minutes later and it will be screaming, it will not go to normal idle by itself.
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you trigger the fast idle cam at startup. after that it should idle down by itself once warmed up and require NO user intervention.
If your fast idle cam does not return the engine to normal idle rpm then there is an issue somewhere that needs addressing.
you can manually override this of you wish but it should do it on its own. it is the point of the fast idle cam and the steps built into it.
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You guys both have good valid points, i only tend to agree with blazer because i have never seen a GM factory v-8 (from the 70's) kick down entirely on its own.
However, my question STILL stands, what and how do i make an adjustment to make this fast idle drop down simply, quicker? Regardless whether the choke does it on its own or i have to tap the pedal.
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Well, i read that link very carefully. And the guy that wrote it sounds like he knows what he's doing. I am starting to believe that my carb and choke is operating perfectly, like i said, it does kick down, but it takes a little longer than normal, probably due to the fact i have no heat riser valve in the manifold. I do however have a new heat stove unit and pre-heater hose to the air clnr assy snorkel.
It looks like the choke is not getting hot enough fast enough and maybe installing a heat riser valve will fix that.
I was hoping i could cheat a little and make a tiny adjustment and get the engine to kick down a little faster.
I think it works a lot like a grass trimmer or hand held leaf blower. You MUST lift that little choke lever and push the little clear rubber bulb to squirt a little gas in to start. If you push the choke lever down, it stalls out. But as that little engine warms up, now you can push the lever back all the way and your screaming and ready to go.
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Weird how this post became a carb/choke issue, and totally got off the post title. All good.
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if you look at a fast idle cam you can see how it's curved and has a couple of steps. as the engine warms up the choke is warmed up and the fast idle cam rotates and falls down the steps and decreases the idle.
This will only work properly if ALL of the choke components are hooked up properly and set correctly which includes the air flap in the air cleaner which needs a vac source and the heat riser tube.
problem is most of our trucks are missing most of this stuff so we get used or think that our truck is normal when it's not.
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Obviously you can manually kick it off of fast idle but it is designed to work automatically. The only manual input should be at first startup by depressing the accelerator to set the choke. If it's not coming off of fast idle you need to either manually "deal" with it or fix it.
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Can i stop by one of these saturdays, and we'll have a look see? I'm 10 min. up the road.
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From my experience the steps of the fast idle cam are also to provide various choke settings due the whatever warmth stage the engine is in. No engine needs ckoke when the temperature is 105 degrees, yet as the temps cool there are varying needs for choke. Below freezing and full choke is definitely required required. But what about when the engine has already been driven for many miles and is then shut off for twenty minutes at 30degrees? The engine cools but not completely, full (high idle) choke would not be necessary. The mi-metal spring and stepped cam deal with it.
I tend to agree with Blazer>
My original point from your question in post 20 is the electric choke is not totally automatic. It still requires driver input.
If you start up cold with the choke set to highest idle and don't touch anything, come back 30 minutes later and it will be screaming, it will not go to normal idle by itself.
Every carbed vehicle I have ever owned new or not was the same way. However, when the high idle is adjusted properly the engine should be 'screaming', but running at about 1200-1400 rpm.
Since the sixties the rule of thumb to driving a cold engine is that it fine to take off immediately if the temp is at freezing or above if driven gently with no stomping on the foot feed. Below freezing to about 15-20, warmup for a minute or so, and below that warm up until the a small blip of the throttle lets the ckoke come off. If the choke is working correctly it will NOT drop off of high idle until the spring is warm enough. The colder it is the longer this takes. Having the heat stove and moving hot air up to the snorkel aids in warming the engine faster but is not necessary. Mostly it's for preventing carb icing at around fifty degrees ambient temp.
YMMV
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The original question....
I know my setting is 8 degrees btdc, the manual states that as well as the decal on top of the rad support. But that is for a stock factory application.
How do you determine your timing when you make changes or modifications? Such as a different carb (different barrels) or the intake or even a different engine? What do you use as a reference?
First and foremost to setting timing is to be absolutely certain there are NO vacuum leaks anywhere. The PVC valve is clean, the brake booster is in good working order, and no lines are pinched or age hardened.
Then you best bet is to buy a book on timing and read it. SuperChevy online has some good articles as do other HiPo sites on Chevy's. Timing can get complicated, the vacuum can, the advance weights and the initial all need to be balanced for the setup engine. No two engines are the same. What works for me at 900' elevation likely will not be optimum for someone else at 3000' elevation. A very good vacuum gauge, a fairly accurate digital advance timing light, a host of springs and weights for the distributor, and an adjustable vacuum advance canister will make whatever you have scream to the best of it's ability. Don't forget that stock plug wires will get you from point a to point b, but good after market wires will get you there quicker.
Now which comes first the carb or the timing? Ask that of ten mechanics and you will get very different answers. The fuel ration has to be right to get efficient combustion BUT without good spark igniting it .....????
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You guys both have good valid points, i only tend to agree with blazer because i have never seen a GM factory v-8 (from the 70's) kick down entirely on its own.
However, my question STILL stands, what and how do i make an adjustment to make this fast idle drop down simply, quicker? Regardless whether the choke does it on its own or i have to tap the pedal.
Assuming the linkage is adjusted correctly, when you first start and you blip the throttle hi idle should drop to a lower hi idle.
reduce initial spring tension on the choke coil. Tighter on longer, looser on shorter. Make a mark so you can go back to your starting point if needed.
If you have rivets on the choke coil you will need to carefully drill them out and replace with correct screws.
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(http://images.tapatalk-cdn.com/15/12/24/2a37f853eeaf71a1295ef5e57f8d8e36.jpg)
With the choke fully closed and on the high idle step of cam.
The green lever connects to the choke Coil and the choke flap.
The silver half butterfly looking deal to the right of the green lever is the top of stepped cam and is also top heavy and operates with gravity.
It operates independently from the green lever and strictly by gravity.
The green lever only holds the silver lever from rotating and dropping down by resting underneath it. The other end of the silver lever is the stepped cam which is hard to see under the bottom of the choke housing.
When the engine starts the pull off retracts via vacuum and opens the choke flap slightly and pushes the green lever fwd and down away from the silver lever which does not move because the throttle linkage and return spring are exerting pressure on the the stepped portion of the silver lever at the bottom where it's hard to see.
This is why you have to blip the throttle to release the throttle return spring pressure from the stepped portion of the silver lever to allow the silver lever to drop down by gravity ( remember it's top heavy) to the second step again at the bottom where you can't see it.
Ok the silver lever only goes far enough to the second step which is your lower hi idle setting because the green lever which was moved by the pull off is still underneath the silver lever just lower.
Now as the choke element heats up and rotates the green lever down out of the way completely and also opens the choke flap.
With the green lever out of the way again we blip the throttle to release the throttle linkage and return spring pressure on the silver levers cam lower step so gravity can pull the top heavy side of the lever down and the Lower part of the cam moves out of the way of the throttle linkage ( the part under the choke housing that's hard to see) allowing the linkage to drop to normal curb idle which is controlled by the screw on the drivers side.
Remember the silver lever controls the hi idle speeds via the steps and the screw on the linkage and operates completely by gravity and being top heavy. It will not move if the throttle return spring pressure is being exerted on it even if the green lever is out of the way.
That's why we blip and that's why its not totally automatic.
Hope that helps understand how it works.
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WOOHOOO! Good! Good! Good! Exactly!
Was that too enthusiastic? Good explanation anyway.
I was starting to think I was losing my memory about chokes not being totally automatic. I didn't really want to drag out the extra Q-jets or Holley's I have sitting in the basement.
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Thanks, glad it wasn't confusing.
Had a extra assembled quad handy.
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Doesn't everyone that owns a quad have a few extra sitting around? Notoriously temperamental carbs. When they work they work awesome, touch them however and all bets are off from then on. Holley's are more idiot-proof, I like Holley's...DUH! ;)
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After reading post 52 about 35 times i was able to follow it. I'll try a slight less tension on the coil. Thanks for the input.
Also, refresh my memory. Timing adv connects to manifold vac right? And how about the sensor on top of snorkel?
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No, timing advance goes to ported above the throttle plates, otherwise, your timing would always be advanced at idle (high vacuum).
I don't really know about the snorkel thing, never ran an engine with a stock air cleaner, I have always used a 6" tall K&N on everything with a splash guard around the outside.
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Ok, got it. Oh and which way do i turn to lighten up on the choke coil spring? Wait, ported vs. manifold....now that's a BIG discussion!
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Clockwise, mark before you start so u can go back.
Small adjustments make a big difference.
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Some have a little tab that won't let you move it. (Later Models) All depends on what you have and where you got it.
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(http://images.tapatalk-cdn.com/15/12/26/784d0541cf1d96acd15011289be12a8a.jpg)
Here's a hot air style with the arrows. Lean is less rich is more tension.
Full or ported. What works best for you? I run full manifold. I have run it both ways. Lots of info on here about that. It's about idle quality cause once you hit the gas vac goes away until rpm's stabilize.
Like you said that's a discussion in its self and don't want to start a feeding frenzy.
You covered that on your other post anyways.
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http://forum.73-87chevytrucks.com/smforum/index.php?topic=32085.0
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Major update!! When I dropped my truck off for new valve seals, the mechanic rearranged some of the vac lines and set the timing to 8 btdc, no advance at all. Well I rearranged all those vac lines according to "rich weyand", advanced the time to about 12 btdc and moved the choke coil just a micro fiber to the right. I don't have the technology to explain what happened, but the engine is much quicker, smooth as silk and better on mileage. Oh, and one of those little tubes under the air clnr assy was pinched. Tomorrow morning I'll know how it is regarding the high idle-kick down issue.
Romans 8:2
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(http://images.tapatalk-cdn.com/15/12/26/784d0541cf1d96acd15011289be12a8a.jpg)
Here's a hot air style with the arrows. Lean is less rich is more tension.
Full or ported. What works best for you? I run full manifold. I have run it both ways. Lots of info on here about that. It's about idle quality cause once you hit the gas vac goes away until rpm's stabilize.
Like you said that's a discussion in its self and don't want to start a feeding frenzy.
You covered that on your other post anyways.
Wow, that totally makes sense, at first try I dialed it left and it started very chokey and chuggy and then I dialed it right and smoothed out nice. After trying it again if course.
And that is exactly how it ran, now that it's on full manifold, the standing idle is a little low I guess, but as soon as you go it feels real nice.
Romans 8:2
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You can always set the idle higher with the idle screw. Just not before the engine is fully warmed up.
Glad you got the timing sorted out. I would (ETA)>not< (I really need to proof read before posting) trust a young certified mechanic to work on these older trucks, they really aren't taught how to work on them. If the computer can't be flashed the knowledge peters out.
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I agree greybeard, its hard to find an old timer mechanic that was taught on the carbuerated engines. My brother in law is a mech and he says he cannot help me on the carb stuff, as he was taught on EFI. Wish i lived near rich weyand. Haha, (not that hes and old timer).
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Timing a engine is not that hard. There are a few basic rules to follow and from there it's just finding out where the truck performs the best under most conditions.
You can get super technical if you want but it's not necessary.
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Thats right, some guys can do it all by sound and feel. It does make sense.
Romans 8:2
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Thats right, some guys can do it all by sound and feel. It does make sense.
Romans 8:2
Incorrect. You can't properly time a vehicle by ear or feel. You might be able to get it close but it won't be proper.
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Only going by what i've heard. I use a light.
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in a pinch ive done it by ear when i was ignorant, now i keep a timing light in my tool box lol.
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After 30 years of setting timing i bet rich weyand can do it by ear, better than a light. Ha!
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After 30 years of setting timing i bet rich weyand can do it by ear, better than a light. Ha!
Doubt it!
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Well i had to tweak the warm engine idle, other than that, it finally kicks down real nice during the cold fast idle. First it drops a level then right down to a nice purr. And now that the timing is right, and the hoses are back where they are supposed to be, she feels like a butterfly with a 454. Well, maybe not a 454. More like a 305 pulling out of the dealer lot in 1977. Yeah thats it.
Ps. I'm convinced manifold vac is where its at!
http://forum.73-87chevytrucks.com/smforum/index.php?topic=32085.msg270444#msg270444
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Well i had to tweak the warm engine idle, other than that, it finally kicks down real nice during the cold fast idle. First it drops a level then right down to a nice purr. And now that the timing is right, and the hoses are back where they are supposed to be, she feels like a butterfly with a 454. Well, maybe not a 454. More like a 305 pulling out of the dealer lot in 1977. Yeah thats it.
Ps. I'm convinced manifold vac is where its at!
http://forum.73-87chevytrucks.com/smforum/index.php?topic=32085.msg270444#msg270444
Care to say that again please.. You mean the idle dropped on its own without user intervention ;) Of course it did. That is how they are SUPPOSED to work :D
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If your choke is setup properly yes it will automatically kick down for you.. That is the whole point of the choke.
How does the stepped/weighted part of the fast idle cam overcome the dual throttle return springs to kick down automatically for me? I don't see how this works without touching the gas pedal manually.
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Ps. I'm convinced manifold vac is where its at!
http://forum.73-87chevytrucks.com/smforum/index.php?topic=32085.msg270444#msg270444
Care to say that again please.. You mean the idle dropped on its own without user intervention ;) Of course it did. That is how they are SUPPOSED to work :D
I still disagree that the ckoke should fall off on it's own with two caveats...1) the carb has a kicker solenoid to knock the choke off the high step of the carb; 2) the carb is not a Holley. OK, OK, I know we have been talking about Q-jets here and the Holley is a different beast entirely by using a vacuum pull-off canister. But otherwise, as was mentioned by SkinnyG, the pressure of throttle return springs (only) on the high idle (I believe) would overcome the ability of the vacuum pull-off keeping the engine at a high idle.
Point of fact- just because I've done something the same way for forty years does not make it right. The person that I learned it from could have possibly been an idiot. :( I admit I have little experience with Q-jests or or any newer carbs of the same style. I have always used Holley's (except my 74 Monte Carlo w/454 and T400, it had a Q-jet and ran awesome for a reasonably stock smog engine [15seconds flat in the quarter consistently]).
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If your choke is setup properly yes it will automatically kick down for you.. That is the whole point of the choke.
How does the stepped/weighted part of the fast idle cam overcome the dual throttle return springs to kick down automatically for me? I don't see how this works without touching the gas pedal manually.
First I'm no expert on these things but I know a few things from reading and listening.
First you are putting the fast idle cam under tension in the opposite direction of the throttle springs. When you push on the throttle you have set the fast idle as well as put tension on the springs. Measure the throttle springs when the fast idle isn't set to when it is and you will see that you have extended the throttle springs.
So now that the fast idle is under tension from your throttle springs when the truck is running and the choke is opening up because of the heat coil its pull the fast idle cam around and will cause it to fall down a step decreasing the idle and decreasing the tension on the throttle springs.
Once the choke is fully open it has pulled the fast idle cam off its last step and onto the area that returns the truck to its normal idle and no tension is left on the throttle springs. The reason the fast idle doesn't occur during normal usage is because the choke is fully open not pulling on the fast idle cam.
TLDR: Fast idle set = throttle springs placed under tension. Choke rod pulls up on fast idle via choke coil taking the tension off and decreasing idle back to normal.
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Know what works the best and is pretty fool proof once the concept is learned? A manual choke. ;D
However, I wonder if we have been on the same page? As the engine heats up and the choke opens that does not mean the high idle is reduced automatically. But the choke will pull off all the way to an open state. In order to get the idle down it requires operator input....
I had to double check what I was saying and I found this at Hemmings Muscle Machines>>http://www.hemmings.com/mus/stories/2009/10/01/hmn_tips2.html (http://www.hemmings.com/mus/stories/2009/10/01/hmn_tips2.html)
When cranking the engine, you do not want to "pump" the throttle, since this will decrease the signal to the booster and limit or stop fuel flow. If the engine does not start when cranked over for a few seconds, release the key and press the accelerator to the floor one more time to evoke an additional accelerator pump shot.
Most automatic chokes have a "clear flood" mode or "unloader" that is carburetor-linkage operated. If the engine does not start and becomes flooded, holding the accelerator to the floor will force the choke plate open, which will decrease the booster signal and provide more air to lean the mixture.
As the engine warms up, the choke spring tension will be reduced; if the accelerator is moved slightly open, the fast-idle cam will drop a notch and move toward curb (warm) idle RPM. You do not want to aggressively throttle the engine to get the fast idle to drop. As the spring tension is released, the pedal only needs to be moved enough to allow the fast-idle screw to clear the next step in the cam.
If the idle speed does not want to drop, the choke has not received enough heat to relax from that position. You do not want to "blow it open" by whacking the throttle hard, which brings us to a significant point: Many cold-start issues are simply driver error and not a problem with the choke circuit.
The entire article can be read at the above link. It is easier than quoting out of my carburetor books here.
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Exactly and read what you put in italics.
It states exactly what I've been saying all a long. All components of the choke need to be working correctly or else it will not step down.
That means proper choke adjustment, properly setting the lean/rich dial, heat stove in place, the snorkel valve working properly.
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I did have to tap the pedal, but it did not take nearly as long. After all, go back to post 20, look at the bullet "cold engine" see the paragraph just above the shaded area-- "after 30 seconds the idle speed may be reduced"..... I dont think it would say that if idle will drop on its own.
Modern EFI cars drop on their own. My wife always asks me when we are in her car, "why are we just sitting here" and i say, "i'm waiting for the idle to drop".
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First I'm no expert on these things but I know a few things from reading and listening.
Do you have a carb on your truck?
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From the same article, doesn't get any clearer than this.
"""As the engine warms up, the choke spring tension will be reduced; if the accelerator is moved slightly open, the fast-idle cam will drop a notch and move toward curb (warm) idle RPM. You do not want to aggressively throttle the engine to get the fast idle to drop. As the spring tension is released, the pedal only needs to be moved enough to allow the fast-idle screw to clear the next step in the cam."""
Otherwise;
As far as the heat stove and air cleaner mechanisms is to prevent carb icing in cold weather. This only has a minor effect on the choke and can easily be adjusted out if not used. There are plenty of normal operating chokes out there not using the air cleaner heat.
Spring tension sets the choke to closed and sets the fast idle cam to the high step. After start as the choke heats the spring unwinds and opens the choke flap. It in no way is translated to the fast idle cam dropping to the lower setting.
I guarantee you will not find a video anywhere that shows a choke completely operate by itself from high to normal curb idle UNLESS it has an electrical device such as a throttle kicker activated by a thermal switch or computer.
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With all respect to others, i must agree with blazer. I have my engine set up pretty close to stock factory with NO modifications, and it is operating like the owners manual states.
I have never owned an older carbureted engine other than a chevy, so i cant speak of any other make or brand of carb other than a chevy/rochester/qjet-2/4 bbl.
Here is a fair challenge- i'd like to see a chevy manual from the 70's that states in some form or fashion that the idle will drop entirely on its own from a cold start. Car or truck.
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I am confused, are we on the same page? I totally agree with one caveat, no carb will lower it's own idle speed with out operator input UNLESS it has some sort of external kicker (electric solenoid or vacuum) to push/pull the fast idle off. These in fact showed up on smog engines to help quicken up (shorten up) the time the engine was running enriched. Remove that canister and the engine will remain at high idle all day if there is no operator input. The choke will be wide open but the idle will remain high.
The choke circuit is connected to, but independent of, the throttle system. There are two times the choke is impacted by the throttle, once to set it (release the pressure so the springs can set the choke), and once at WFO to clear a flooded state (mostly on Holley's I think). Anything else is simply to let gravity/vacuum/heat do their things. The Q-jet is (I think) unique in that it also uses actually air flow past the upper plate to provide so help with opening of both the choke and the secondary throttle plates. Correct me if I am wrong...
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I still agree with blazer. Dont be confused, just accept what blazer wrote in post 83.
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Quadrajet uses a pull off to slightly open the choke on start. Also Has another function but that's another chapter.
Qjet also has the mechanism to clear a flooded state.
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Back in the day, a lot of guys worked on their own vehicles and having a basic understanding of how a carburetor and timing and the simple functions of an engine operated were much more common. You dont see that today, men working on their cars on a saturday in the driveway, even doing an oil change.
Cars go 15-20k miles per oil change, you never touch the coolant, the tranny, timing, plugs, wires, etc. For the most part you only open the hood to add wiper fluid. And after 300k miles you toss it in the dumpster and get a new one.
And many folk like that, having a reliable car or truck that will always start and be safe, with all the comfort and luxeries.
Glad this site still talks about the trucks of the old days and how carburetors work and how to solve problems and such.
Its nice to keep going on these posts just to learn more, but honestly i'm running out of things to say. Probably because my entire engine is running well, for now.
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Ok, back on this again.... What does it mean if you start up a cold engine, (and its real cold out), drive for several miles and get it fully warm, then shut it off to get gas or something, then when you start it back up the idle is high? You actually have to kick it down again!?
Is too much cool air going to the carb through the snorkel? Should i remove it in the winter?
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The choke coil is external to the carb airflow.
Just the choke coil cooling off and contracting due to the extreme cold.
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Phew!! Thought i was back to square one. Yeah, past couple days, single digits! Thanks