73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Fuel Systems and Drivability => Topic started by: bedwards on January 18, 2020, 09:39:28 pm
-
Bone stock '85 c10 305. I bought it 3 years ago with 19000 original miles. I rebuilt the carb then. It has 40000 on it now. The plugs are almost new, the cap and rotor were replaced last year. I run no ethanol in it.
The truck has run very well all this time. I had one issue with the tank selector valve that was fixed some time ago.
This week it has started bogging under hard acceleration. It cranks and idles well and runs just fine easing around. I wasn't sure what it was so I checked the cap and rotor, then the plugs, replaced the coil, checked the egr, the vacuum secondary, the fuel pump output. The timing is set at 8 btc. I think the engine is bogging after the secondaries open. It feels like its starving for gas when they kick in. Is there an easy way to check the secondary adjustment and why would this adjustment change? Is there is something else I have overlooked? I really don't want to take the carb apart again.
update, the hoses are good, the fuel filter is brand new, the fuel pump pumped a quart in 30 seconds, I put a new coil in it because the old original just barely failed the bench test. I loosened and retorqued the air horn.
The secondaries are under tension. They are cracking open revving the engine in park.
I gently used compressed air to empty the bowl and jets and filled it with carb cleaner and let it set for a while. It cranks right up and idles well. The ignition module is original but it seems to be ok.
I'm out of ideas. I hate to just throw parts at it. I bought a carb kit today. If it doesn't start doing better this week I guess I'll pull the carb.
-
Do you see the Secondary Metering rods rise when you are at WOT? Not while running of course...
-
Yes, they are rising.
-
AFAIK you should not see the secondary flaps moving when revving it up in Park. There should be enough tension to keep them stable. Too little tension will usually cause a bog.
The secondary flaps are held down by a small spring on one end (you can see the flat screwdriver fitting on that end). You loosen the small allen head set screw that is up under the end of the shaft (3/32" allen, I think) and then rotate the flap mechanism with a small screwdriver on the end until the spring just touches the flap (zero tension). Then rotate it further to set the tension based on the specs, and tighten the allen screw. I think the specs are something like 3/4 turn after zero tension, but you would have to check it for your specific carb model.
You might be able to adjust it with the carb on the truck, but its a real PIA to see. Also, that small set screw might end up anywhere on the engine if you loosen it too much and falls out at the wrong time.
Bruce
-
^^^^^ I agree.
-
ok, will try adjusting it next.
-
So is the bog caused by loss of vacuum in the secondary tunnels, due to incorrect tension on the spring?
If so, I have learned again!
-
QJ secondaries operate on a variable venturi principle. The secondaries are fully mechanical, but the air valve responds to engine load and airflow. If the air valve opens too fast the engine bogs because it cannot process the sudden increase in air. Throat velocity decreases, pressure differentials drop and fuel delivery leans. The air valve is tuned to engine load parameters by tension adjustments on the air valve spring.
-
This is why we have fuel injection ;)
-
Well.. I didn't have good luck. Adjusting the screw 1/8 turn clockwise just moved the flat spot higher in rpm seems like so I moved it in the opposite direction which just lowered rpm of the flat spot. Now that a cold front has gone through, it seems to be running much worse. It is surging at lower rpms also. I put the screw back where it was before the adjustments. I vacuum checked the timing and it is working. I also vacuum checked the EGR and it won't hold vacuum but I don't think this is the main problem. I am ordering a new EGR and gasket tonight. I'm leaning towards something in the carb or it is stopped up. It is also harder to start cold than it used to be and like I said earlier, the plugs look like they are running really lean. If the carb were getting in the secondaries too soon wouldn't it cough black smoke?
Did I move the screw enough or should I have gone further?
thanks again for all the ideas
-
there are 3 egr valves listed at Rock Auto. They all look alike. Any idea which one is right?
DELPHI EG10080 OE No 17085765, 17085767
DELPHI EG10081 OE No 17085768, 17085769
DELPHI EG10079 OE No 17085764
-
If the carb were getting in the secondaries too soon wouldn't it cough black smoke?
Did I move the screw enough or should I have gone further?
Black smoke is the result of excess fuel making the engine run rich. Premature opening of the secondary air valve will impose a lean condition. The air valve adjustment is tied directly to the application and is specified by the carburetor number. What is the number stamped onto the left rear pillar of the carburetor? The number probably begins with 170xxxxx.
What is the number stamped into the top of the existing EGR valve?
Check the distributor vacuum advance to see if it will hold vacuum.
-
It acts like its running lean. The plugs look like its running lean.
The carb number is 17085226. I will have to go back up to the garage to get the egr number.
The distributor held vacuum. Like I said, I doubt the egr is causing the lean condition as its not even opening. I can open it with my finger and the truck will idle down. I bought a GP Sorensen kit for the carb #96-519a. If I don't find the problem this week, I will pull the carb and build it this weekend. It worries me that the truck seems to be running worse today but the last time I ran it, it was 64 degrees and today its 30 so the lean condition might be the problem. It seemed to be surging at lower speeds.
The numbers on the egr are: csm 17085768 and 103 51n ( I guess that answers one question anyway)
-
Yes, it does...
It acts like its running lean. The plugs look like its running lean.
The carb number is 17085226. I will have to go back up to the garage to get the egr number.
The distributor held vacuum. Like I said, I doubt the egr is causing the lean condition as its not even opening. I can open it with my finger and the truck will idle down. I bought a GP Sorensen kit for the carb #96-519a. If I don't find the problem this week, I will pull the carb and build it this weekend. It worries me that the truck seems to be running worse today but the last time I ran it, it was 64 degrees and today its 30 so the lean condition might be the problem. It seemed to be surging at lower speeds.
The numbers on the egr are: csm 17085768 and 103 51n ( I guess that answers one question anyway)
DELPHI EG10081 OE No 17085768, 17085769
Air Valve Spring adjustment is air valve just closed plus 7/8 turn (image). Pay close attention to the float adjustment, as well. Make sure the primary metering rod piston moves freely in its bore and that the secondary metering rods didn't drop off their lifting arm.
-
Check your pull off for a vac leak.
-
THanks guys. I ordered the EGR tonight and have the carb kit already. It will be this weekend before I build the carb. I will give you an update.
-
Got the EGR on but figured I'm this far might as well look at the carb. It was a little dirty inside from 3 years use but it wasn't that bad. No water in it. But there was a vent tube laying in one of the wells for the secondaries. I tapped it back in place and staked both of the tubes so maybe they won't move again. I also popped the plug out above the adjustment for intermediate throttle and tapped it for a large set screw so I can take it out and adjust the mid throttle if need be. Its all back together but not on the truck yet. Will put it on in the morning and let you guys know how it is doing.
thanks again for all the ideas and help!
-
Ahhh the errant vent tube...Probably just solved your problem. Tune up of carb settings will be a bonus.
-
ok,, at a loss, no joy. Exactly the same behavior..... :'(
-
Does it recover from the bog after the flat spot?
Does it stumble? Did you check the pull-off for a vac leak? Don’t start messing with the apt. Been working fine till recent, that’s a set adjustment.
Just a note if you hold the throttle open in neutral long enough to have the secondaries open, don’t do that.
-
Rebuilt carb Friday night. Same behavior, cranks, idles and pulls really good up to when the secondaries come in. Then it just bogs down. As soon as you let up on the throttle its fine. I did adjust the APT. I knocked the plug out, tapped and put a big set screw in it so I could adjust it. It was a tad rich but is very smooth now transitioning from one circuit to the other. I have adjusted the spring on the secondary plates from factory tighter as much as 1/2 turn in 1/8 increments and adjusted lighter the same. It wants to pop up the carb if too light and bog if too tight but I can't seem to get the bog out of it.
I have been all over the top of the engine. There are no vacuum leaks. The vacuum timing is working, visually saw it, set it on 4btc although I did have it on 8btc. The secondary vacuum is working. The EGR is working now, put a new one on. At the risk of sounding like a parts replacer, I doubt its ignition with new cap, coil, module, plugs. The wires are 3 years old but its not missing. Just a bog like its too lean. The plugs I took out weren't
that old. The engine used to run rich and it showed on the plugs but now its dead on to maybe a little lean. I can send plug pics but I don't think that's it. I'm going to get a vacuum gauge and see what it tells me this week. I'm not sure which port to use for it unless just one of the base ports.
I don't think its a cam, wouldn't be running bad at lower or missing rpm for a bad cam? There is no missing. Smooth as silk.
-
i can say this, my mud truck would bog if i floored it, if i i got into it slowly it was ok. after just dealing with it and a few years later after finding more about timing i set base to 16° so my total was around 32 or so and hooked the vacuum advance to manifold vacuum. totally different engine. i cant remember if i messed with the carb screws any but want to say i had to tune it in a little
-
I was running 8btdc but was getting a little ping at tip in, but its not much difference at 4 so I'm probably going to put it back on 8.
-
if your getting ping at 8 something isnt right. has your motor been worked on? (i.e head/block work)
-
I'm about one more day away from getting tired of this and ordering an Edelbrock or Holley. I don't want to spend the money and keep the truck bone stock but I am real tired of the quad. I've built and tuned a lot of carbs but this one takes the cake.
Leaning towards an Edelbrock 1400, good price, made for egr, vacuum secondaries, elec. choke and similar gas hookup. Will need an adapter from square to spread bore intake.
Any suggestions?
-
no Irish, its bone unmolested stock with a little over 40000 miles
-
is your egr hooked up?
what plugs you have?
-
Which tube fell out small or large. Large is your POE, if driven in too far will block passage to 2ndary feed hole just above air valve plates on the air horn and draws fuel when they start to open to prevent a lean surge. (Pull over enrichment)
-
egr is hooked up just put new one on as I found old one was not holding vacuum, I was running Ac Delco 44ts I think. I was one range cooler than the book called for to try to minimize pre-ignition. I put new Accel 0566-4 in it Sat. I was grasping for straws hoping it had a bad plug. Its not missing though.
The tube that fell out was on one side of the secondaries, the larger diameter tube, thinking it was a vent tube? THere is a longer tube with a much smaller orifice on each side also. I put it back Friday night and staked both in place so it won't fall out again.
-
have you tried high octane fuel?
whats your engine temp at?
the eld 1400 is a 600cfm carb. thats too much for a 305 you need a 450-500 carb unless youre turning over 6k rpms. imo i either try to go with holley or quad. i dont know if your carb is bad or not. if its rebuilt then it should be ok. i would try to eliminate as much crap off your truck as you can as far as emissions. the ping as you know is either from high combustion chamber temps (wrong plugs or overheating) lean fuel condition, wrong octane or timing too far advance. i would try to tune the carb to its base settings, advance the timing as far as it can go (but i wouldnt be below 12).
-
The truck has always pinged just barely at tip in. I've had it for 3 years now and got it with 19000 original miles. It still had the factory settings. I just always thought it didn't like today's gas. I have run Seafoam down the carb to try to de-carbon it.
I built the carb back then and drove it till last week when all of a sudden it wouldn't take the secondaries.
I just priced the transition to an Edelbrock carb and its ridiculous. All the add-ons to keep the egr, the cruise control, the air conditioner solenoid.
The Holley may be more initial money but less ad-ons so the total may not be much different.
I guess I could go with a rebuilt Quad but I wish I could make sure that its not something else before I drop the cash.
Know of anyone local Birmingham, Al. that could build my quad since its very low mileage?
-
What part of town are you in.
I don’t rebuild carbs any more but I can check your work for you.
-
Barring a mechanical issue unrelated another thing to check is the plastic 2ndary actuating cam that lifts the rods. 2ndary rods not raising high enough can cause a lean condition.
You went lean on the secondary side causing your ping and dead spot all of a sudden. Something changed.
Your ADP is mostly for cruise condition on the primary side when high vac is present the rods are all the way down in the jets.
Lean Surging while cruising 2000-2500 rpm caused by the primary rods being too low, raising the ADP allows more fuel on the the primary side.
Also blow through your Poe holes carefully with carb cleaner and the red straw to see if the tubes are clear that you reinstalled.
The tubes are also fed from the secondary fuel wells that are supplied with fuel from the main fuel bowl through a small orifice that can get clogged.
-
What part of town are you in.
I don’t rebuild carbs any more but I can check your work for you.
I live on the Warrior River but work in Fairfield weekdays
-
Barring a mechanical issue unrelated another thing to check is the plastic 2ndary actuating cam that lifts the rods. 2ndary rods not raising high enough can cause a lean condition.
You went lean on the secondary side causing your ping and dead spot all of a sudden. Something changed.
Your ADP is mostly for cruise condition on the primary side when high vac is present the rods are all the way down in the jets.
Lean Surging while cruising 2000-2500 rpm caused by the primary rods being too low, raising the ADP allows more fuel on the the primary side.
Also blow through your Poe holes carefully with carb cleaner and the red straw to see if the tubes are clear that you reinstalled.
The tubes are also fed from the secondary fuel wells that are supplied with fuel from the main fuel bowl through a small orifice that can get clogged.
The plastic actuator is there and working. I blew cleaner and compressed air in the tubes when I had it off last Friday. The smaller tubes with the orifice were much harder to tell if they were open but I believe they are. I did bend the metal holder for the metering rods putting it back together like an idiot but I got them back like they were. That wouldn't explain the sudden loss of secondaries before I worked on it Friday. Is the metal holder adjustable?
-
Bedwards I am in Roebuck but I will be glad to look at the carb if there is no one closer.
I wish Blazer74 lived in town every thing he has said is spot on.
-
I just read an article on how to adjust the secondary hangers and what measurement. I guess that's next.
-
Bedwards I am in Roebuck but I will be glad to look at the carb if there is no one closer.
I wish Blazer74 lived in town every thing he has said is spot on.
I appreciate that. If it comes down to it I will take you up on it.
-
I might help if you posted a few pictures of your carb.
-
how do I save pictures. I was going to up load some of my spark plugs last night and couldn't resize them small enough to post.
-
See if this works
Click on :
Reply
Attachments And Other Articles (near the bottom of the page.)
Browse
Find the picture on your computer and double click on it. Or click once and click open.
Then paste your text.
Post
-
Yes the hangers can be tweaked for the secondary they also have different letter codes for different heights Hangers.
41/64 If I recall correctly the measurement for that and it’s considered a performance hanger. (A) hanger would be the highest (K) hanger would be lower. The secondary rods also have letters on them to designate size.
I would put your secondary door spring pension back to factory specs and bend that hanger Tabs
just a little bit to raise your rods up a bit see what that does.
Take measurements at your starting point so you can always go back.
Use the holes where the rods attach for measurements to the air horn with the hanger in it’s full up position.
-
How to upload pics to the forum (http://forum.73-87chevytrucks.com/smforum/index.php?topic=6428.0)
-
Take measurements at your starting point so you can always go back.
My version of "Save As", or "Take Pics" 8)
-
Yes the hangers can be tweaked for the secondary they also have different letter codes for different heights Hangers.
41/64 If I recall correctly the measurement for that and it’s considered a performance hanger. (A) hanger would be the highest (K) hanger would be lower. The secondary rods also have letters on them to designate size.
I would put your secondary door spring pension back to factory specs and bend that hanger Tab that rides on the cam just a little bit to raise your rods up a bit see what that does.
Take measurements at your starting point so you can always go back.
this is what I am trying next, today was just to rough at work to come home and mess with it =]
-
it is carb # 17085226 first pic is plug that came out with several thousand on them the second plug pic is the new plugs I had it it last time i drove it Sat. All the plugs look similar.
-
Bone stock '85 c10 305 ... I had one issue with the tank selector valve that was fixed some time ago ... the hoses are good, the fuel filter is brand new, the fuel pump pumped a quart in 30 seconds....
After reviewing your opening comments and without detracting from all of the suggestions and guidance you have received thus far, did you ensure that the tank selector valve motors full rack? When you said the hoses are good, did you verify that none are kinked or perforated? Any chance the fuel filter behind the carburetor inlet nut is backward? What were the fuel pump draw and pressure measurements? What is the float level spec that you used? What happens if you lockout the secondaries so that they cannot open and then accelerate WOT?
-
After reviewing your opening comments and without detracting from all of the suggestions and guidance you have received thus far, did you ensure that the tank selector valve motors full rack? I tried both tanks more than once. The gauge moves, not 100% sure of the valve, but knowing how its made inside, more than likely. When it failed last time, it pumped fuel from one tank to the other and when that tank was full into the evap canister and when it was full flooded the engine through the vent. I did replace the canister at that time.
When you said the hoses are good, did you verify that none are kinked or perforated? Its metal from pump to carb, Will have to get under it to see at the fuel selector valve
Any chance the fuel filter behind the carburetor inlet nut is backward? verified, rubber end with ball towards fuel line
What were the fuel pump draw and pressure measurements? I don't know how to measure the pressure with what I have but it pumped almost a quart in 30 seconds of cranking it is the original factory pump though
What is the float level spec that you used? 13/32, it did not need moving from where it was last time I rebuilt 3 years ago
What happens if you lockout the secondaries so that they cannot open and then accelerate WOT? I will have to try this, not sure
carb kit was a GP Sorenson 96-519A from AutoZone
I am assuming that there is an electronic aux enrichment on passenger side front. It has a solenoid and what looks like a power valve underneath that it opens. All I did was clean it and put new gasket on. Not sure how to test function and there wasn't anything on how to in the instructions. I guess I could check with ohm meter to make sure there is resistance there
The carb fuel bowl was not really cruddy inside and there was no junk or water in it, but it did have a bathtub ring around it where the fuel has been.
I appreciate all your thoughts and help
-
Under the circumstances, I recommend making sure that you adequately cover the basics, especially those that could manifest "suddenly" since that seems to be how the symptoms developed. IMHO, unless the cause is obvious, only after the fundamental of adequate fuel supply to the carburetor has been substantially verified should you pursue a diagnosis, repair, alteration and fine-tuning or replacement of the carburetor.
- Rubber hoses connect the steel fuel supply line (and return line when used) to the fuel pump, the tank selector valve and the fuel tanks. Check them all to verify that none are collapsed, kinked, split or otherwise perforated. Be patient and wear safety goggles to keep falling debris out of your eyes.
- To check fuel pump draw and pressure you need to borrow, rent or purchase a vacuum/pressure gauge that accommodates 30 "Hg vacuum and 15+ PSI pressure. They are available from auto parts stores for sale/rent (sometimes for free with a refundable deposit) and Harbor Freight for sale, etc.
- Try locking out the mechanical secondaries to determine whether symptoms disappear or are in fact directly related to secondary opening.
- The solenoid protruding from the top right side of the fuel bowl cover controls an accelerator pump enrichment circuit that should have no bearing on the symptoms you described.
- The 'bathtub ring' inside the fuel bowl probably reflects water contamination sometime in the past.
-
Ok, will be this weekend before I can report back
thanks again
-
Fuel pump is jumping from 0-5 lbs while cranking. It also does not hold pressure. Is it supposed to? Anyhow, there is a new Delphi pump on it but was too tired to finish it tonight. Will blow out the lines and get it cranked tomorrow. The lines are good and flexible, no kinks. New fuel filter too although the one in there was not 2 months old.
-
The fuel pump should draw >20 "Hg and build/maintain 5-7 PSI pressure. The pump has internal check valves that may be leaking or a ruptured diaphragm. Drop some oil from the engine dipstick onto the tip of a clean finger. Does the oil maintain a tight circular puddle with defined boundaries or does it quickly track out along your finger ridges?
Did you install the new Delphi fuel pump before or after posting the "0-5 lbs" measurement?
-
Put the new pump on after testing the old one. I figured the pump should hold pressure. It had been hard to start cold and the choke is working. I figured its letting the fuel drain back. I'll check the oil. It hasn't made oil and it smells like oil and not like gas but will let you know.
-
Ok, I guess I am officially one of those people (Parts re-placer)
It was the fuel pump all along. It runs really well now. It should, its got a bunch of new parts. It faked me off when it pumped a quart of fuel 30 seconds and I didn't have the gauges to check pressures then.
It wants to tink just at tip in if I go to 12 btdc so it is set at 8 right now.
Should I back off the secondary spring or leave it? It is at roughly 1 turn from just touching right now. Factory was 3/4 turn.
BD your right about starting with the basics.
Many Many thanks for all your suggestions.
-
The factory secondary air valve adjustment is 7/8 turn (see my earlier post - the information was quoted from the factory service manual) so set it accordingly or leave it where it is for now. Follow the other members' guidance if you wish to fine tune the carburetor beyond the stock configuration.
The image you posted of your new spark plugs indicates the plugs are running slightly hot. Next tune-up, consider dropping one heat range, which may decrease the engine's sensitivity to detonation and pinging.
-
Glad you got it sorted out.
Speaking of spark plugs what is the plug in that last picture?
-
It's an Accel 0566. Bought them shooting for a cooler plug. The porcelain and the tip don't go as far in as the Delco's that came out and the Delcos were one range cooler than factory specs. I am changing the oil tomorrow although it sat thick on my finger without spreading out. I did put a big plug of grease on the pump pushrod to hold it in place and hopfully the oil washed it away and I will get it out with an oil change.
tell me what you think of the plugs: