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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: 78ScottsdaleK20 on December 06, 2007, 05:20:04 pm
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I have a 350 bored .030 over. SpeedPro RV Torquer .448 lift 214 duration 112 LSA. Speed Pro Hypereuctectic flat top pistons, Edelbrock Performer EPS, Edelbrock 600 cfm #1406. HEI with 50,000 volt coil, and Heddmen Headers running through 2 1/2 inch dual exhaust. SM 465 trans.
Since new I have never been able to tune this carb in right. Changing rods, jets, springs, etc. Get tuning close, holds for a little bit, then starts to run erratic. I have replaced 3 Intake gaskets due to a suspected vacuum leak. I have checked with carb cleaner and propane to no avail. Last Intake gasket change, engine performed flawlessly, for 1 day, then erratic since. Spark plugs arent showing same type of A/F. #6 and #8 more rich fouled than the others. Timing has been set at 10 and 12 degrees BTDC. Found 12 is best. I get fine dirt particles in the float bowls, and have just put in new fuel filter (clear). All linkage especially throttle shaft, choke linkage, and air bleed screws gets pretty dirty. I clean them periodically.
I have a basic timing light, so I have not set total timing. I will be putting a timing tape on the balancer and making marks on it to check for total timing and do the valve lash adjustment. I should be able to check total timing with a basic timing light at the timing indicator if balancer is marked, correct?
I have put approximately 15k on the motor, and as of now, I am hearing some higher pitch chatter coming from the valve covers, sometimes it sounds as if the push rod has excessive play, only after a slight increase in RPM's. Is it common for a necessary valve lash adjustment neeeded at this mileage? Could my mysterious vacuum leak be coming form mal-adjusted valves, or even excessive worn valve guides?
This engine has been pretty good thus far...starting every time, and not acting too erratic, just needs some of that advanced tuning to be just right. So any other ideas, comments, or suggestions are welcomed.
Thanks,
Mike
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So what exactly is it doing? Does it idle poorly? Does it have poor acceleration? You should pull the fuel inlet off and take the air horn off of the carburetor. Remove the floats, the needle and seats and remove the factory sock filters. I never re-use them. Make sure the float level and float drop are set correctly. You may want to upgrade the needle and seat.
Explain more of your driveability symptoms.
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The idle and driveability for the most part is ok. The idle lopes a little (jumps around 200-350 RPMs) and shouldnt with this mild cam. Almost acts like it missing. But it also could be carb metering.
I had the carb jetted really lean, 2 1/2 stages lean and the A/F was spot on. Then a month to a month and a half the A/F got really thin (lean). So I bumped the jets and metering rods fat back to base calibration and seems to be the best there, but really fat at idle and cruise, and thin at part throttle.
Vacuum readings pulledat idle from the Intake are an average of 14" hg with a rapid floating needle between 13"-16". The throttle is opened and vacuum drops to 0"-2", raise back up to 20" with a rock steady needle with RPM's around 2,000-2,500.
Vile I will take your advice and tape a vacuum gauge to the windshield and take some readings as to what the engine is doing. This will give an accurate and real world scenario with engine load. I have have been eyballing an MSD ignition box for a while, but havent done enough homework to decide which one would be best for my application. Any suggestions...?
Thanks for the reply.
Mike
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An MSD 6A with a distributor and coil would be a great improvement. It also sounds like your timing is too retarded. TRy advancing it and then check your vacuum readings. If your needle is still boucing I would suggest a compression test.
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Definately set those floats man. I just rebuilt an Edelbrock 1406 and is was WAY off on float settings. I bought it from its original owner who let it sit and never cleaned it. It had never been opened up or rebuilt before me. It was seriously like bottomed out and then as soon as a touch of fuel came in, it would close the needle cause it was set too low. Now it runs fine since I rebuilt it and reset the floats. Also, go ahead and check your valves again, pull a valve cover and prepare to get messy. Loosen each valve with a 5/8" socket until it taps, then tighten until it stops and go 1/8 to 1/4 turn more.(stop and back off if you hear it sucking through the intake.). IT helps if ya cut out an old valve cover across the top, the you can just put a couple red rags(shop rags) over the valvetrain and move them over as you need them. It's gonna be a lot of oil, min saoked the fender today when I ran mine. My carb seemed like it had a dead spot in it until I adjusted the valves. I had one a bit too tight and three that were just barely past ticking. Now I am doing fine, no more erratic idle, no more seemingly missing engine, and a lot better takeoff. Of course, that's just a suggestion.
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Floats were set correctly previously. Here are some Vaccum readings I have encountered.
During Idle, the needle on the gauge violently drifts between 13"-16".
When throttle gradually is opened, vacuum drops to around 10" then picks up vacuum usually around 20".
While driving, at idle vacuum is same as listed above.
When throttle opens gradually, vacuum drops to 10", cruises at 15-16", and wide open throttle is 0". When decelerating vacuum is just under or at 20". A/F ratio goes lean anythign under 12", unless you in the power mode, then the step up function kicks in and goes rich.
I expect the readings mentioned above with the exception of the idle, to be of the norm. Maybe a little less vacuum at idle, but even steady would be nice. I am definitely starting to hear the valvetrain cry out to me for an adjustment. More at higher RPM's than at idle. So I will set the valve lash today when I get off work and take some more readings.
The vacuum gauge I tested with was kind of a cheapo, and had some diagnosis marked on it. When at idle the needle fell to the area marked as late ignition timing. The timing is set at 12 degrees BTDC. If the timing was late wouldnt that be ATDC??? ??? I should know this, but for some reason am now confused...If the timing is advanced wouldnt that be BTDC and retarded would be ATDC???
I may take some more readings with the Mity-Vac I have somewhere in the garage. If I get a little extra time I will do a comp test and get back here with some results...
Thanks for the replies and suggestions. I'll check out the MSD ignition boxes. I bet that is a sure fire way to know that you are using enough juice.
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Have you ruled out the power brake booster assuming you have one. They will act up and then be fine for a while causing a vacuum leak. Just a thought.
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That's a good idea ZIEG but I have checked that. At least I have checked for vacuum leaks before the check vlave and after.
Brake booster is connected to the back of the carb. There is an inline check valve and I tested for pressure between the carb and check valve and after the check valve at teh brake booster. There is no pressure loss at the Brake Booster, but there is a slight pressure drop (1-2 psi drop after 2 minutes) after the check valve, (between the carb and check valve) if that makes sense.
Its my understanding that this check valve is one way, and really is not required, its there in case brakes fail you get a couple of reserve pumps to the pedal. My brakes are extremely touchy, they work great almost too good to the point, where they lock up too easily. Especially when wet.
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I would re-adjust your valves -Personally I like to do it from zero lash -not while running. What is your timing at at 3,000 RPM's?
If you are still getting fluctuating readings do a compression test.
You should have a check valve on your booster. Some have a backfire valve too.
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I have not checked what the timing is at, at 3,000 RPM. When I install the timing tape on the balancer, to mark it when I do the valves, I will also mark it at the 28-38 degree marks so I can check the total timing. Ido not have an advanced timing gun just the basic.
I should be able to check total with these marks from the tape. Speaking of total timing, at what RPM should total timing be checked at? And should this be checked the same way base timing is set, with the vacuum advance plugged?
Thanks.
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Leave the vacuum advance hooked up and Set it at around 36° An advance timing light is a good idea but if you put a bright dot where you want your total advance that will work too.
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So I called the engine builder and asked him what the advanced timing should be set at. He recommended a guy he uses to set the distributor up. $30 later and he can dial it in depending on the cam, CR and what I am using it for. In a real world situation, this is my daily driver and that would mean having it down for however many days it takes him. Not gonna happen, when you work six days a week, and work at 2 am.
Sooo...I gave in and bought an advanced timing light, and checked timing. Base is set at 12 degrees BTDC, and programmed the light for 28 degrees (out of curiosity more than anything) and it came in on the 0 degree mark on the balancer at 2,400 RPM's.
The builder also said that some chatter (sounds like a typewriter) in the valvetrain with a little bit of a cam is normal, and unless its obvious or a knock is heard then it is probably fine. I also told him about the last Intake gasket change and how the A/F and performance of the engine was perfect then went bad, he mentioned that it could be a possibility that the center blocks of the gasket for the crossover could have blown out (meaning maybe not so much completely gone but torn), causing the erratic A/F and lack of performance.
Whatever it is I cant wait to tear into the Intake AGAIN! >:( and check the gaskets. I may do this anyway to see just how exact the fitment of the head and Intake match up, and also ensuring the gaskets are trimmed to match the port. That might be a job for later.
For now I would imagine most of you following this thread are thinking why havent I tried a different known good carb to check and eliminate that possibility...me too. I took the carb off tonight and put an insulator on and cleaned up the carb and put it back on. Throttle shafts and linkage get pretty gunky on this motor.
Called it a night since it was 20 degrees outside and my hands were soaked with carb cleaner.
I'll do some more tinkering with it and just maybe I can get this thing nailed. How about changing up the weights and springs in the dist? If my base timing is set at 12 BTDC, and I advance the timing light for 34-36 degrees, shouldnt the mark fall where the base was at, which was at 12 BTDC? Doing this with the vacuum advance hooked up correct?
Thanks
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Where your zero marks line up on the balancer is where your timing is at based on the reading on your timing light. So if at 3,000 RPM you line up your mark with zero on your pointer whatever the light says is your timing. Try to get 36° total advance. It's always a good idea to tune your advance. Make sure the weights are moving freely. Make sure the vacuum advance is working correctly. Try running full vacuum advance at idle and adjust your base idle speed accordingly. Don't be too concerned about base timing.
As far as having a noisy valve train (sounding like a typewriter) is NOT normal. Re-adjust your valves from zero lash on the base circle of the cam. Example #1 TDCC adjust the rocker arm until you have no up and down movement of the pushrod. Twisting the pushrod can give you a false sense of lash. Make sure you take your socket off of the rocker arm when you are verifying lash because if you leave the socket on there it can seat the rocker also giving you a flase reading. Once you acheive zero lash tighten the rocker 1 full turn. Do this for both the intake and exhaust valve on #1. Then rotate the crankshaft clockwise 1/4 turn and do the same in the order of the firing order until you have adjusted them all. TDCC #1, rotate 90° adjust #8, rotate 90° adjust #4 etc (1-8-4-3-6-5-7-2). Also make sure none of your pushrods are bent.
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To eliminate as a factor, I checked the ignition circuits. Measure ohm resistance with the plug wires, and my readings were with the shortest wire 3.5 to the longest wire being 5.6. This was taken with the multimeter set at the 200k ohm setting. Chiltons calls for NMT 30k ohms of resistence. I think I am ok there if my readings are correct.
Took measurement of the primary coil resistance between the TACH and BAT terminals and got 0.9. Chiltons calls for "less than one ohm or nearly zero." Checked the secondary resistance between the rotor button and the BAT terminal and got infinite reading (no reading on the meter). Checked the resistance between the GROUND terminal and the button and got 12.9. Chiltons calls for both to be between 6k and 30k. With an infinite reading between the BAT terminal and ROTOR mean the coil is bad?
"Replace coil only if the readings in step one and two are infinite." So went to NAPA and put a known good coil in the distributor and checked the primary and secondary, and got the same exact readings. They checked the module and it checked out ok.
When I took the rotor off the distributor the screws were loose, and there was ALOT of carbon and fine metal shavings on the underside. Condition of weights and springs are slightly rusty but otherwise good-no bindage.
So in long, I imagine the ignition components are good, and that leads me to believe it must be fuel metering. Have not set the valves yet since it is snowing outside and freakin cold.
Feel like I am spinning my wheels here...so I will go out and have some more fun.
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General rule here -No more than 3K ohm per foot for ignition wires.
Set the timing and readjust your valves.
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If all that don't work, plug ur brake booster hose off and drive it and see how it does. Be VERY CAREFUL as the brakes are gonna be a real bear to stop with. If you still have issues your booster is okay. Mine did the same, no leaks at chek valve or anywhere on hoses, had an internal one some where. I ended up setting mine at 4 degrees without the vaccum advance. Runs like a champ.
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Dinked around with it some more. My total timing is at 28 degrees. 12 BTDC and at 3,000 RPM it took 16 degrees on the gun to hit the 12 degree mark on the indicator.
How do I get more advance at 3,000? Change weights or springs. I have a weight and springs set. Came with three sets of springs and one set of weights. I havent mucked with the adjustable vacuum advance since I dont know which way does what, so I would have to check but think its at around 5 turns out.
Installed a thick Holley carb spacer/gasket, (one you would install to keep the fuel colder) and cleaned up the interior of the distributor and under side of rotor (was pretty dirty), also installed spring loaded needle and seats, so I can keep her running when wheeling. END RESULT: better vacuum readings, the needle does not violently flicker, stays steady at 15". Adjusted carb with the gauge and got it to 16" at idle. This made the A/F really rich, so I dropped 1 1/2 stages lean for the power and cruise mode. Re-adjusted for highest vacuum with new metering rods and jets, still rich, but not as bad.
It seems I am getting closer, its still running pretty fat, both at idle and cruise, but the part throttle stills stumbles a little.
The engine ground strap is the same as when I bought the rig, and looking pretty old. Might replace this and install another one on the other side of the motor. Currentlly there is only one from the pass rear header bolt to the cab.
Might take the dist. into have it put on a machine and have the guy dial it for my application. After all, it might be worth the little $30 investment to know that it is right.
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??? I'm confused. Don't you have a zero mark on your timing tab? Aim for zero and whatever your gun reads to make the mark line up with zero is what your timing is at. Don't worry about base timing right now. Advance the distributor (rotate it counterclockwise) until you have 36° total advance.
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Maybe I am confused too...instructions say to take base timing (12) then take readings again advancing the gun to line up the balancer mark to where the base was set at. It took 16 degrees to get the balancer to line up with the mark from the base reading and then add the two totalling 28.
Maybe this is incorrect. I will try again. If I advance that distributor any more the terminal for the BAT and TACH will hit the firewall, and the vacuum advance is going to hit the Intake. Should be able to positon the cap in any position as long as your not off a tooth, and the rotor is pointing to the correct wire right? I need to reposition the cap so I can advance it more.
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Do you have a body lift or drop or something funky going on? Your distributor should not hit the firewall. If the vacuum advance hits the intake so you can't get 36° then your distributor is off one tooth.
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Took more timing readings, and it took 51 degrees advance to get the mark on the balancer to line up with the zero on the tab. Took timing with everything hooked up as normal running operation.
This seems wrong, and yes the vacuum advance will run into the Intake with a little more turn. Could the dist. be off one tooth and still run pretty good, just not perfect? This may be the cause of the miss (I thought it was carburetion).
Also I noticed that my fuel pressure fluctuates...Like my RPM's it will flutter sometimes, dropping to 3 psi then go back up to the 5 psi I set it at. Needle will flicker. The fuel in the filter (clear) gargles / bubbles and there is little fuel in it. The filter itself is of a bigger kind and is positioned just before the pressure regulator.
When I get enough time I will yank the valve covers off and verify valve lash.
Thanks for the replies, it helps.
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If it reads 51° total advance you might want to verify your TDC mark. Bring the #1 piston to TDC visually (pull the spark plug) and see if your mark lines up on the damper with your timing pointer.
51° is over advanced.
As far as fuel pressure goes -with a carburetor pressure isn't as important as volume unless pressure gets too high. Anything over 9 PSIG can easily force the needle off of the seat and flood the carburetor. But if you see it bouncing around like crazy I would do a fuel volume test with the regulator installed.
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So I am tired of working on this heap out in the cold so I took a break. Sometimes you gotta just walk away from it >:(
I retarded the timing back to 8 BTDC (from 12) and total timing as anyone would expect fell 4 degrees to 47 @ 3,000 RPM's. Quick math would tell me that if I wanted to get 36 total I would have to retard the timing all the way down to 3 degrees ATDC. That cant be right.
As far as verifying TDC with the mark on the balancer and the indicator, the engine builder set TDC and I havent mucked with it. I verified TDC with the balancer mark and indicator when I put the dist. back in when the Intake gasket was done, and I know that I didnt set it for cylinder #6. As far as being a tooth off, anytime I dropped the dist. in it would only go in matching the oil chamfer. If I went one way or the other, (one tooth over) the dist. would drop but not seat on the Intake. So I should be spot on.
I have set the carb up with the vacuum gauge, and since then I have set the idle mixture screws way fat from where I used to have it. A/F improved a little and driveability, but has the infamous stumble at the low end during part throttle.
I found the tech article on CK5 forum about "timing & advance timing 101 tech post" and is informative, almost to the point complicated to a shade tree mechanic as myself. However I did take advice and disconnected my vacuum advance from the timed port on the carb and hooked it up to direct manifold vacuum. It seems this helped a little with the above mentioned A/F and driveability.
Soooo...at this point it seems I will muck around with weights and springs in the dist. to get the correct timing set. If that all fails, IM PUNTING!!! Let somebody else do it. :( Sometimes its just nice to learn yourself...Also will set correct valve lash this weekend when I get the time...
Thanks again Vile for your continued support! 8)
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A good aftermarket distributor should really help you nail down your timing. Get rid of the vacuum advance distributor all together if it's in your budget. It sounds like your distributor is in right since you can range up over 50° before it hits.
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Also did you pull the air horn off and pull out those sock screens then readjust your float level/float drop?
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I heard that one whould stay away from teh dist. without vacuum advance from that tech 101 page writtenb by an X-GM engineer. It mentioned that most street driven engines really benefit from them, if used correctly.
So far when changing timing, I dont have any knocking or pinging, so I am thinking of advancing the timing til I hear some pinging then backing it down. This may bring me to where I was or more advanced then before, but install different springs to slow the centrifugal timing down. Its my understanding that experimentation is the best way here if you dont have a dist machine.
I did not take out the sock filters, as there was quite a bit of debris found in one of them, and I felt if these were removed I would have more problems with erratic A/F metering if any of that debris goes through the metering system. My thought is, better to stop it there than have it clog up the jets and all little orifices in the carb. Should I still remove these? Do you recommend doing this if dirt is found consistently in the fuel bowls?
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If you are using a good quality inline fuel filter they are a catch can for a lot of crap. If you have a good filter the smallest particles will pass through and not build up in the fuel inlet. I've always eliminated them but at the very least clean them and the passage way.
As far as vac advance goes- If you are running a really good aftermarket ignition system and it's more of a toy than a DD I would kick it to the curb. If you are daily driving you will probably want a good vac adv dist.
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Followed valve lash instructions verbatum using the method of marking the balancer every 90 degrees, and starting with #1 following the firing order. Loosened the rocker arm until lash was felt (up and down movement of rod) then tightening locking nut until lash is zero, then half a turn.
I felt side to side play in the rocker arm and the push rod spins easily. Should the rocker arm be snug with no movement, and the push rod able to spin easily? I thought no, so I adjusted the rocker nut until all rockers were snug and a little spinning of the rod. Some took 1/2 turn, and some took 2 full turns.
Started truck up (engine cold-outside temp 28) and heard a little excessive valvetrain noise until engine fully warmed up. Still can hear the slight "typewriter" sound once fully warmed up.
I also verified somem more ignition components. One test for the pick up coil continuity between the two leads. Suppose to be between 800-1500 ohms resistence with no break in continuity when actuating the vacuum advance arm. The reading I got was 804 with the reading dropping down to 795 when moving the vacuum advance arm. I gues this little difference is ok as long as its not a big break. Also took the weights and springs out of the dist. and cleaned off a little gunk from the bushings.
However, the engine performance feels a little better, like the valve timing has improved. Still have the infamous low end stumble (though it seems not as bad as before), I imagine is from fuel metering. Still runs rich at idle and cruise, and lean at part throttle when throttle is just opened up but not quite in the power mode. It seems I have to run this in the power mode so its not in lean mode stumbling around.
I will continue to search for this common problem in the forum and other forums like Hotrodders and CK5 and fumble around with carburetion to see if I can correct the low RPM stumble. I shouldnt have to live in the power mode to drive this thing around, unless I like stopping at every gas station. :-\
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One full turn from zero lash is what you wanted to do. Yes the rockers will be able to move and if lubricated the pushrods will spin without much effort so you'll need to readjust your valves. Start that one over from the beginning or you'll be bending pushrods.
P/U coil is 500-1500 and usually you'll find around 800ohms. The pick up coil will either work or it wont. So rule that out or you'd most likely be dealing with an intermittent no start.
Re-adjust your valves again
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If I tightened the rocker nuts too tight, there is a possibility of the following?
1. Bend a rod
2. Damage a lifter or rocker arm even braek a spring
3. Wear the cam lobe down
If they are too tight, will I hear some noise of the above mentioned?
Since I tighten the rocker nut enough to take out the side to side play in it, but the push rod is still able to be spun, is this so tight, that I could do damage?
The next time I will have time to redo this is tomorrow. Not sure if I should be driving this thing around... ??? I drove it around last night and a little this morning, and I did not hear any bad noises...
I will re-adjust the lash again just to make sure. When I get to zero lash (rod to rocker arm) its one full turn. If the rocker arm still has movement, is this acceptable. I thought maybe thats where you get the valvetrain noise from...?
I am sure you are aware of, there is many different amounts of "turns" to correctly set the lash, from 1/8 of a turn to Chiltons 1 1/4 turn. Last question, how do you know how much turn you need?
Thanks again for your support and help, its appreciated!
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1 full turn of the rocker arm nut from zero lash will be just right. Yes the rockers will still be able to move. Let us know how you make out after you have them set
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Will do Vile, thanks again for your continued support. I said this before, but it really helps out when we have a site such as this willing to help other people out.
I will set the lash again this afternoon, might squeeze in a comp. test as well. This will only verify the possibility of other issue I may be having.
Now that I think of it, I can tell the difference in how the power band reacts with the way I have the lash set right now, compared to previous. Now I have very little low end and its all in the late mid to upper RPM power with a lot of fade towards the very top.
Will check back later after all is done. good thing I installed those Fel-Pro $45 rubber gaskets :o under the valve covers for a quick on and off.
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So the valve lash is set. I rummaged through some of my Chevy High Performance mags and found the latest one on valve lash setting. With your advice Vile, and all the others I read on how much to turn, the rockers, rods and how it feels against the lifter, (you can feel it preload) I set it on 3/4 turn from when I felt just the slightest resistance turning the rod, once lash was at zero. This should be about the same as what you suggested with 1 full turn. I wasnt far off as the typewriter sound is very minimal. Drives like it is a little better.
I think it might have been a little off before I set it the first time. Still having metering problems with carburetion, but that is a whole seperation issue, that I will regretfully say I can fix with about $400 from Holley ;) Unfortunately thats gonna have to wait until I return from Hawaii in March. At the same time the top end will get replaced with better heads and maybe an Intake. Should be a screamer after that!
BTW, I noticed when replacing the dist. cap, I had #1 at TDC and rotor in position for #1. When I put the cap on, I noticed the rotor tang didnt exactly line up with #1 on the cap. Could the be due to the advanced initial timing of 12 degrees? Or should the tang on the rotor match perfectly with the #1 on the cap? Maybe the dist. is off one tooth as you suggested before? I have tried numerous times during misc. wrenching, and the dist. would only drop all the way in one way. But I have heard other people having their dist. off one tooth. ??? Also, when I pulled the plugs, #'s 1,7,4, & 6 were black and sooty=rich. The others were clean... ??? Not sure what this could amount to, other than maybe my carburetion.
Anyways, I have said it before, but thanks again Vile. This thread is long, but maybe it can help others as well.
Mike
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Depending on how advance/retarded you timing is the rotor will not be pointing at the #1 post. If the distributor is off a tooth, or you need to move it a tooth to get more advance, you have to pull it out and turn it and drop it as far down as it will go to engage the camshaft and then have someone bump the motor over so the oil pump shaft will align to the new posistion.
What is you timing set at now? How much vacuum are you getting at idle? What is you idle speed set to?
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Initial timing is set at 12 BTDC. Currently I am getting approximately 14-16" hg vacuum at idle. It drops down to around 8-10" hg at part throttle, then up to 20" hg when you come off the throttle decelerating. The idle speed has always been set at 800-900 RPM's.
Each time I re-jet the carb to improve A/F, I set the idle air mixture screws with the vacuum gauge plugged into direct manifold vacuum. I have found for best vacuum it likes idle air screws 1.5-2.5 turns out. This is way too rich as I get the lack of performance, and black sooty plugs.
If I back the screws in the lean it out, then the vacuum drops to around 14". I have also noticed some oil accumulation at the rear corners of the block, looking like a slow head leak. Could be from the valve covers too though. Its pretty popular to leak at the corners of the covers.
If the head is leaking, even a little in the lower corners, could this cause weaker vacuum readings? I doubt the head gasket is failing, I dont get the milky oil.
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Drove the truck around, and it drives like a dog. Stumbling, hesitating, no power, running really lean-then really rich...
I thought of something after reviewing the carb manual for the umpteenth time...
If the carb operates according to engine manifold, should direct manifold be applied to the front main orifice located at the center of the carb? I have the PCV line hooked up to this. This line is from the valve cover, and would it provide enough or if any at all, vacuum to properly operate the carb?
I am thinking that direct manifold vacuum should be applied to that center orifice. I feel a little silly right now, not thinking of this before, but that was how the old engine was hooked up. But it was a quad-jet with some other provisions hooked up to the carb.
If this is the case, I need a different area to put the PCV line to. It basically comes down to this...This engine is as basic as it gets, as far as there is no smog equipment, no EGR, or heat riser, or vacuum lines besides the vac advance. The crankcase ventilation off the pass side valve cover is going into the bottom of the air cleaner (open element 14"x3") and the PCV line off the drivers valve cover into the front of the carb. I know I should inclulde a pic...slow :( computer would take me a week to upload a photo.
Soooo...I will have to test this change out to see if there are any improvements. I stopped by the Dyno shop of the guy who referred me to the engine builder, and I balk at throwing them $300+ to have the engine tuned. I know that they will do a tremendous job, since one of the guys teaches advanced auto at the local community college and drag races, and he was my teacher at a vocational skills center.
Well, I will fiddle around with it and post any results I find.
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Your carburetor doesn't work like that. Manifold vacuum is at that port on your carb and the PCV hose should be hooked up to it. Sounds like you have it right already.
You keep saying you have low vauum, it's a dog etc. Now that your valves are properly adjusted I would check for either incorrect valve timing.(timing chain) Are you sure you have good fuel volume? (kinked fuel line, bad fuel pump etc.)
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Ok, I was trying to brainstorm ideas. It just made sense since there is oil on the PCV valve itself and a little on the outside, I thought maybe if this is a line that vacuum is being pulled from the carb, that maybe some oil is being pulled in too, richening the A/F...? Like you said before, maybe thats not how it works though.
I did have a set of valve covers on before ( a while ago) without a baffle under the cover and oil was being sucked into the carb running it rich. Of curse now it is baffled, but there is a little oil on the PCV.
I will not have time to rip of the front of the engine to verify the timing chain, since my son is in town tomorrow for two weeks, (could be a training session though ;D). If it did stretch, this would lead to incorrect valve timing, right? It is a double roller. Has 15k - 20k miles on it, do they stretch this early?
Whats your opinion on the engine spec.
350 4 bolt main
Flat top Hypereuctectic pistons (supposed 9.5:1 CR)
Speed Pro RV Torquer cam .448" lift 214 duration @50 112 LSA.
Stock 882 heads with 1.94 Intake 1.60 Exhaust (supposedly 76cc's...questions the CR).
Edelbrock Performer EPS Intake
Edelbrock #1406 600 CFM carb
What kind of vacuum readings would you expect? I told the engine builder 14-16" hg was my idle vacuum, and he said "that's pretty good". I hear that number should be a little higher, more like 16-18" if not full 20" hg vacuum with this cam. It's certainly not radical, but no stock either. When I do get the full 20" of vacuum by letting of the throttle hard the A/F is perfect.
The way its all set up, the A/F is better, the more vacuum I have.
I am going to have to do a comp test and do some digging around. The next time I reply to this topic, its gonna have to read something like this...
GOT IT! I switched heads cam and carb. The truck just lost its paint job from pinning the throttle to the floor. Now Im on my way to the tire store, cuz Im gonna need to replace those too. Thanks Vile!
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Who installed the timing chain and gears? Has it ran like this since the cam was put in?
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The timing chain and gears were installed by the engine builder and have been the same since the motor had 0 miles. Ditto on the cam. It only started running like this recently.
Not sure if the winter fuel blend (10% ethanol) is a big factor. It certainly doesnt respond well in wet or damp weather.
I am really thinking the problem lies in carburetion/ignition. Reason is, it sometimes it runs where it should be, just not consistently. I can even hear and feel when its running rich, lean and when it runs good.
The point is, I am guessing that the timing chain, gears, cam, and valves must be working properly, it just seems that the Intake, Carb, and ignition are not communicating with each other properly at the correct time.
What I really need to do is perform substitute tests. Substitute in a known good carb. Check results. Substitute a known good dist. Check results. Clearly I am not doing the right things to get the corrected results. So some of it is testing equipment, and some of it is knowledge of which way to go for improvements for tuning.
I'll have to fiddle around with it some more in my spare time and check back.
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Well I would definitely say you have an ignition related problem if it runs poorly when it's wet out.
Make sure you have a good coil, the cap is good and the carbon button is good. Check the rotor, and check all of your plugs. Mist the wires and see if it runs poorly after you get them wet.
As far as fuel goes again make sure you have good fuel volume from the pump and then maybe you should rebuild the carb. Clean all of the passages with a piece of mig wire or mechanics wire. Blow shop air through all the passages.
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I have replaced the cap and plugs. The internal parts of the dist. have not been replaced or the wires (2 years old though).
Yeah I agree with you on the ignition problems. I rejetted the carb last night to 1 stage rich for the cruise mode from base stock calibration and the A/F and driveability is way better. Still lean and stumbles at off idle...but better.
Drove it in to work this morning, and it was raining and really wet out, and sometimes (most of the time) it didnt want to idle when coming to a stop.
I will replace the dist. and wires and see what results I get. Next would be replacing the fuel pump, since teh fuel pressure gauge still fluctuates.
Is it normal to see very little fuel inside the filter, and for it to perculate? I imagine if there is some kind of fuel starvation, the filter will not accumulate the correct amount including fluctuating pressure.
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i had a truck that ran like that it was dampness in the cap so i did a all out tuneup and it ran super
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Drove it to work this morning and ran great. It ran the way every engine should run. A/F was right where its suppose to be, and driveability was good. Still lean down at the bottom, but overall alot better than before. BTW it was a crisp cold, but dry morning.
I still may replace the wires, and definitely rebuild the carb this weekend. This may provide a good learning tool for the boy. He's into race cars, trucks and motors as is most 8 year olds.
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He's into race cars, trucks and motors as is most 8 year olds.
My 3 year old loves race cars, tractors, and of course, trucks. He pretends his chair in the living room is his truck.