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post #1 of 67 (permalink) Old 02-18-2018, 11:54 AM Thread Starter
 
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Poor Running

Im trying to figure out whats going on with my 69 LeMans. I rebuilt the 350 motor and break in seemed to go ok. After break in I have been having problems getting it to idle and it does not want to accelerate. When I set the initial timing to 12deg it runs (~10"inHg in park), but seems like it wants to stall out. When I put it in gear it bogs down and stalls out. I noticed that when I pull the vacuum line off it doesn't change the idle at all. I can bump the timing up to 18degs and it runs better but still irregular. When I put my hand over the air horn it doesn't pick up speed.

When I advanced the timing to where I got it to run, I took it out for a spin and it has almost no power. I give it gas and it almost acts like its choking and wants to die. If I back out of the gas it will start to slowly accelerate and then it will pickup once its in second gear and ~2200 rpms or so.

Does anyone have any idea what could be going on?
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post #2 of 67 (permalink) Old 02-18-2018, 02:43 PM
 
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10" of vacuum? Do you have a really big cam? Maybe too much for the engine and you have lost idle quality and bottom end power? If a big cam, did you make sure you had enough clearance between the top of the piston and valve at maximum lift so the valve is not kissing the piston?

Wrong intake? Single plane intake vesus a factory 180. You will lose bottom end with the single plane intake and it will begin to pick up at higher RPM's.

Timing chain/gears installed a tooth off. Did you use a degree wheel? Cam could be retarded which will hurt bottom end and pick it up at top end RPM's.

Vacuum leak? New PCV valve & grommet?

I assume the carb (type?) is OK, ie new, rebuilt, and in good working order. No gas smell from flooding over? Too lean? Not too large or mechanical secondaries?

Valves adjusted too tight or incorrectly. Have you pulled the valve covers while the engine is running to make sure they are all operating and lifting the same height - ie worn down a lobe on the cam during break-in?

If you milled the heads and did not check your valve geometry at the rocker arm/valve stem to make sure it is positioned correctly, you could have a valve or two being held slightly open. Had another member (or 2) that experienced poor engine performance due to this. Zero lashing the valves with the use of poly locks took care of the problem in one instance and the other found a poly lock too tight and had to re-adjust a valve to fix the problem.

Stock exhaust manifolds? The heat riser valve could be stuck shut if stock exhaust manifolds. Even exhaust flow coming out of both pipes?

Blown head gasket? Have you pulled the plugs after running to inspect for both rich/lean running or water?

A number of things to check.
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post #3 of 67 (permalink) Old 02-18-2018, 08:04 PM Thread Starter
 
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10" of vacuum? Do you have a really big cam? Maybe too much for the engine and you have lost idle quality and bottom end power? If a big cam, did you make sure you had enough clearance between the top of the piston and valve at maximum lift so the valve is not kissing the piston?

Wrong intake? Single plane intake vesus a factory 180. You will lose bottom end with the single plane intake and it will begin to pick up at higher RPM's.

Timing chain/gears installed a tooth off. Did you use a degree wheel? Cam could be retarded which will hurt bottom end and pick it up at top end RPM's.

Vacuum leak? New PCV valve & grommet?

I assume the carb (type?) is OK, ie new, rebuilt, and in good working order. No gas smell from flooding over? Too lean? Not too large or mechanical secondaries?

Valves adjusted too tight or incorrectly. Have you pulled the valve covers while the engine is running to make sure they are all operating and lifting the same height - ie worn down a lobe on the cam during break-in?

If you milled the heads and did not check your valve geometry at the rocker arm/valve stem to make sure it is positioned correctly, you could have a valve or two being held slightly open. Had another member (or 2) that experienced poor engine performance due to this. Zero lashing the valves with the use of poly locks took care of the problem in one instance and the other found a poly lock too tight and had to re-adjust a valve to fix the problem.

Stock exhaust manifolds? The heat riser valve could be stuck shut if stock exhaust manifolds. Even exhaust flow coming out of both pipes?

Blown head gasket? Have you pulled the plugs after running to inspect for both rich/lean running or water?

A number of things to check.
1. It is a rather large cam. I didn't think it would be that bad, but it's a [email protected] 0.050 intake cam. I actually had the motor run really well with a larger cam, but that cam did fail. No interference.


2. And 5. I am running a stock manifold and quadrajet that I rebuilt with guidance from cliff ruggles book. It doesn't seem to be flooding as I really think I could smell it.

3. The cam was degreed and it lined up with the dots.

4. Pcv valve and grommet are new.

6. This cam was checked after break in and the lobes are good.

7. I did have the block decked 0.023 and used the same pushrods. Could that really be the issue? I am using stock length push rods and poly locks. I have set to zero lash then 3/4" of turn so it should be 0.037" preload.

8. Stock manifold woth the rise stuck open. It is a single exhaust but a larger muffler. It was on it when I got the car amd I suppose it could be getting clogged up. The exhaust was fine before I parked it 2 years

9. I don't think it has a blown head gasket, but that would be something to check. All the plugs have brown/Tan insulators with dry black soot on the nose.

When I try to accelerate it seems so slow. It wants to go to 3000rpms creeping then shifts hard into 2nd and continues to be slow until I gain speed and then it gets better.
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post #4 of 67 (permalink) Old 02-18-2018, 08:23 PM
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Re-check your rocker adjustment to make sure they haven't changed. I had to re-read your post before I saw that you're running poly-locks - so that does make your valve train adjustable. The stock Pontiac system with bottleneck studs is non-adjustable and sometimes folks make that mistake. 212 @0.050 is not a "big" cam by any stretch of the imagination. It should be making a LOT more than 10" of vacuum at idle though, I'd expect at least 16" inches or more so start looking for vacuum leaks. Check all the hoses, power brake booster, intake manifold seal, etc. A quick way to check for intake leaks is to get a can of spray starting fluid. With it idling, carefully spray it at all the points where the intake meets the heads. Use one of those long tubes like comes with cans of WD40 to try to hit the underneath sides of the ports too. If doing that makes it speed up, you've got a leak at that point.

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post #5 of 67 (permalink) Old 02-18-2018, 09:37 PM
 
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Agree with Bear - not too big a cam and you should have more than 10" of vacuum. Typically, I back the poly locks off until the you hear the clicking sound, then slowly tighten until it goes away. Wait a few seconds for the lifter to normalize and if no more clicking -good. If it begins to click again, then tighten just a little more until it stops. Once the rocker arm stops clicking, turn it 1/4 turn and lock it down. Personally I think 3/4 may be too much, but I also know each company has their own way of doing this, and 1/4 a turn has always worked for me.

I would try to figure out why you are only running 10" of vacuum. Look for the obvious and do the test as BearGFR pointed out. If you have power brakes, the grommet at the booster can dry and crack and the check valve that goes into the grommet can also go bad. I might simply plug the fitting on the carb and fire it up to see if there are any vacuum changes. You don't have to drive it, just check your vacuum reading with it capped off. Again, it may be too tight on the rocker arms so I would re-do these and see if the vacuum increases - watch your vacuum gauge as you adjust them.

The black sooty end of the electrode could mean a little rich. New air cleaner element? I assume points? I like to keep the plug gap at .035" whether I use a hotter coil or electronic ignition. If you have points, have you checked the gap/dwell? If they have been sitting for a while, they may be in need of a light filing to clean them up and then re-gap and set the dwell.

Try one thing at a time and let us know on the progress, eventually it will get worked out.
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post #6 of 67 (permalink) Old 02-20-2018, 11:11 AM Thread Starter
 
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Thank you both for your suggestions!

I am glad to hear the cam isn't too big, I sure didn't think it would be. Running rich shouldn't cause it to run so terribly should it?

I'll check for vacuum leaks. I plan to make a home made smoke tester soon. I'm hopeful that a vacuum leak is all that's wrong.

I been lashing the valves cold. Should I run it for a few minutes to make sure the lifters are pumped up and firm? I also did 3/4 of a turn since crower specs out 0.025-0.050" preload (half to a full turn). Is adjusting with the motor running a superior method?

I have also kept the plug gap at 0.035" with Delco rs45 plugs. Awhile back I tweaked the dwell by ear and that smoothed up the idle a little but that didn't cure the problem.

The air cleaner is a 2 year old open element, but no miles on it. Many times I've worked on it I leave it off anywaus just to work with the carb.
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post #7 of 67 (permalink) Old 02-20-2018, 03:29 PM
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My money is on a vacuum leak - a significant one, unless your valves are a lot farther out of adjustment than it seems like they might be. Hydraulics are self-adjusting to a degree, especially at idle - they just have to be "close". If they were off enough to look like a vacuum leak that significant I'd expect there to be other symptoms that would show up at idle, like a significant miss-fire. I assume you've checked all the other 'easy stuff', like making sure the distributor is indexed correctly, and assuming the timing chain is "right". I think the recommendation for setting the rockers "hot" with it running is a better process for getting things dialed in. What you're shooting for is getting them tight enough so that they're quiet, but not so tight that pump-up at RPM starts to throw things off - it's a better way to "fine tune" the settings. However I don't think the difference in procedure between that and how you did it is enough to cause what you're seeing.

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post #8 of 67 (permalink) Old 02-20-2018, 08:20 PM
 
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Are your distributor weights advancing? They could be stuck and when you try to accelerate you give it fuel, but it also needs spark advance, from the weights and increasing rpm's.....if they are stuck, or on wrong or not there you will get little or no power. The car will still run.

Also your dist vac can,.....is it hooked to full or ported vacumn.....and how much timing is the can pulling? You have to get this right, lots of these cans pull in too much timing, and with your very low vac, I would bet you may be getting a little at idle and what little you gets drops off soon....

Check the weights and springs are moving freely and that vac can is pulling and how much...you need to assess you timing before carb issues, of course as the gang said could be many things valves, rockers etc. But get timing right first.
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post #9 of 67 (permalink) Old 02-22-2018, 12:53 PM Thread Starter
 
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I have verified that the weights move and I have messed with the weights and I know it made a difference, but it's been too long since I messed with it. Im fairly certain I switched to using the heavier weights to smooth out the idle park to drive transition (400 rpm drop).

The vacuum advance is full manifold vacuum. Ive always had smoother idling motors with full vs ported. The crane adjustable vacuum can is set to pull 14degs. I had inital set to 16-18 to smooth it out. 12 was almost diesel like super rough and didn't respond to removing vacuum hoses. And yes I set initial timing without vacuum advance.
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post #10 of 67 (permalink) Old 02-22-2018, 06:22 PM
 
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I have verified that the weights move and I have messed with the weights and I know it made a difference, but it's been too long since I messed with it. Im fairly certain I switched to using the heavier weights to smooth out the idle park to drive transition (400 rpm drop).

The vacuum advance is full manifold vacuum. Ive always had smoother idling motors with full vs ported. The crane adjustable vacuum can is set to pull 14degs. I had inital set to 16-18 to smooth it out. 12 was almost diesel like super rough and didn't respond to removing vacuum hoses. And yes I set initial timing without vacuum advance.
OK, I am not sure I am getting this correctly, so bear with me. You have full manifold vacuum to the vacuum advance. Your vacuum advance is factored at 14 degrees. Your initial setting at the crank is 16-18 degrees. If you take away 14 degrees of vacuum advance because that is what you get with full manifold vacuum, then your initial timing at the crank with the vacuum line disconnected would be 2-4 degrees - way too low.

Now if you have your initial setting at the balancer at 16-18 without the vacuum line disconnected and then you hook it up to full manifold, you now have 30-32 initial - waaay too much. Add in your mechanical advance in the distributor and you have yourself a time bomb just waiting to detonate itself apart.

You should set your initial at the balancer between 10-12 degrees and then bring in your mechanical and add the vacuum to that IF you plan on running full vacuum to it. (Initial + Mechanical + Vacuum Advance on full engine vacuum = Total advance)

You also need to know when Total Advance is in. With the ethanol gas, it should be anywhere from 2800-3200. Some will go as high as 3500 RPM, but this is something you have to play with using the springs/weights of the mechanical advance. Lemans guy will be able to answer better on this one.

Keep in mind that if you have an original balancer with the bonded rubber that these can slip and the marks will be off and setting your timing to them will be off. And, you want to make sure the correct harmonic balancer is matched to the correct timing cover and scale. People swap things around and they won't match, again, throwing timing off at the balancer so you cannot use it. I assume all your parts are still original to the 350. Did you happen to degree the balancer along with the cam?

Just for fun, disconnect the vacuum advance & plug the line. Set your initial at the balancer to 10-12 degrees. Take if for a test drive.

Now if the engine sounds crappy, with vacuum line plugged and disconnected, loosen up the distributor hold down bolt/clamp just enough so you have to use a little effort to rotate the distributor. Rotate the distributor right (Counter Clockwise - CCW/retard) until it runs rough. Note the position. Rotate it back (advance) the other way until it runs rough. Note the position. Now move it again counter clockwise until it runs nice and smooth. If it sounds slightly rough because you went to far, simply move the distributor back until it smooths out again. Leave it there, and take it for a spin. The distributor won't move because it is fairly snug, but can still be moved by hand. If you hear ANY pinging under load, back off the gas as that is detonation and bad for the engine. Distributor is too far advanced and you can pull over and turn the distrib. by hand a small amount counter clockwise to retard ignition - test again. If it ran good on the first drive out, you can also pull over, advance the distributor (Clockwise) by hand a tiny amount, and try again. Again, NO PINGING should be heard under load. If at a point you hear any pinging, you want to retard the distributor by turning it a small amount by hand and try again. Repeat until it goes away under load. Timing is now set regardless of your timing marks which you can check afterwards.

This is timing the distributor/engine by ear and how many do it and is how I do it to fine tune the timing once I get the initial set-up at the balancer. Just have to make sure you listen for the engine pinging and back out of the gas immediately and adjust the distributor - retarding it slightly counter clockwise.

Now if you want, hook up the vacuum advance to a ported source on the carb. It is my understanding that the Crane vacuum advance is not adjustable with regards to vacuum, but rather, to how quickly the 14 degrees comes in, so keep that in mind - you will always have 14 degrees total and that cannot be changed, only the speed at which the 14 degrees kicks in.

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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, LeMans & GTO Engine Tuning and High Performance

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