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Its been a while since I last posted due to life getting in the way. I am getting back to working on my 52' 300 trying to get it ready to enjoy this summer.

It all started when I had issues with the accelerator pump in the carb not working and not allowing me to accelerate. So I ordered a rebuild kit from Max Merritt and rebuilt the carb. Got everything put back together and got the car fired up with using the base fuel screw settings of 2 turns out. It was idling higher than I would have liked, so using a dwell/ tach meter, I am able to watch the RPM and dwell with the car running. Currently the Dwell is set to 24 degrees which is within the spec of 21-30 degrees according to the service manuals. These measurements are taken with the Vac Adv disconnected at the carb and the carb plugged off. I cannot get the idle down to the factory spec of 450-500 rpm without the car dying. Currently its idling around 750-800 RPM with the Vac Adv connected, but has an audible miss at idle. It smooths out when given throttle.

I thought that the timing may be off since it won't idle at the correct RPM. After checking the timing with a timing light and Vac Adv disconnected. It is right on at 6 degrees BTDC which I believe to be within spec. When I check the timing with the Vac Adv connected, the timing jumps up to 16-17 degrees BTDC and continues to advance further when RPM's are increased. It has the Delco distributor if that matters.

My questions to the experts:
1. Is the timing supposed to be set to 6 degrees with the Vac Adv connected?
2. Is my advance of 16-17 degrees with the Vac Adv connected seem reasonable. Is this due to the RPM's being elevated above the normal spec of 450-500 RPM?
3. I assume if I can get the RPM to 450-500 then there shouldn't be any timing advancement from the Vac Adv? If its still advancing at 450-500 RPM is there any adjustment to the vacuum canister to reduce the advancement or does it need rebuilt?
4. Any other suggestions or areas to look at?

thank you for any insight or help you all can provide.

You will need to set your base timing with the idle down in the 400-450 range. Otherwise, the centrifugal advance inside the distributor begins to kick in and you will get a false reading. I just had in a 52 with the idle set way high. When I got that cranked down it turned out the timing was about 8 degrees retarded which explained the overheating and poopy performance.

At low idle the carb is so constructed that the vac advance receives no vacuum and thus does nothing. I usually don't bother to disconnect them when checking timing --I just make certain the idle is good and slow--and there is no need at all to plug anything.

A short observation will show if everything is basically correct: while using your timing light slowly give gas. In very short order, the vac advance will kick in and the timing will jump. Give more gas and the timing will slowly increase with speed as the centrifugal advance does its job. Then snap the throttle shut and the timing will instantly jump way back as the vac advance goes out of the picture. Then as the engine slows to an idle the timing will return to base.

Ross,

Sorry for such a long delay in responding. Several other issues have shown up and have been taking care of those first. I thought I had a vacuum leak at the manifold so I pulled the manifolds off to replace the gasket and also had the manifolds machined as an assembly. Turns out that the hardline from the vacuum pump to the wiper motor has a short section of flexible line it it that I could not see before removing the manifolds. The fuel tank was full of rust and severely clogged the fuel line to the front of the car. I have run a temporary hose from the rear of the car to the front for now and installed a boat tank in the trunk as a temporary solution until I can get the engine to run like it should. I have an inline filter before the pump and the factory filter between the pump and the carburetor. I also have a fuel pressure regulator and gauge between the pump and the carb. The pump seems to put out 8-9 PSI at cold startup, and then slowly drop down to 4 and sometimes it will drop to 0 PSI all while the car is still running (but not well). The fuel pump was replaced last year with one from Max Merritt, so I assume it is still in good shape.

I was having issues getting the idle down to spec and ended up adjusting the throttle linkage from the pedal to the cross rod that runs over the motor. The throttle linkage from the pedal was hitting the body seam and not allowing the carburetor throttle shaft to fully retract when no throttle was applied. I have been able to get the idle down to ~500 RPM. The engine will run, but does not idle smoothly. I have connected a vacuum gauge to the manifold port on the intake manifold and get a bouncing needle between 12 and 15 inHg. This is with the vacuum advance disconnected at the carburetor and the port plugged. The timing is currently set at 10 degrees where it seems to run the best, but still runs rough. I feel like it runs smoother when its cold, but as the temperature rises it starts running rough. If I raise the RPM up, it smoothes out. Spark plugs have been changed and are gapped at .028 with an Autolite 303. Dwell is at 25-26 and I believe it should be somewhere from 21-30.

A few follow up questions:
1. How important is it to have the spark plug wires not crossing or touching each other? Most of mine seem long and are touching. Could this cause the miss at idle if the spark is crossing over into other wires?
2. Since the vacuum reading is lower than ideal, what are some tests to do that would help identify if there is a valve issue causing the low vacuum?
3. Could the timing chain be stretched? could that cause the need for additional timing?
4. Could a worn distributor shaft cause any of these issues.

I apologize if any of these things seem elementary, this is the only carbureted vehicle I have ever worked on. This car is twice as old as I am.

I appreciate any insight or suggestions you or anyone may be able to provide.

Thank you,
Grady

#3— remember that the timing chain correlates the crankshaft and camshaft position, not the camshaft and distributor position. So your timing light will always tell you accurately how the valves are behaving, assuming the valve train and distributor are in reasonable condition. The only thing it won't tell you is whether the piston timing is aligned with the valve timing.

Usually the recommended maximum timing chain deflection is a total of half inch from side to side.

It should not matter if your plug wires are touching unless the insulation is breaking down. Fire it up at night sometime and with no lights nearby open the hood and have a look. Let your eyes adjust and look for glowing and arcing.

Your jumpy vacuum says that there is a valve problem, as does the fact that it gets worse as it get warmer. Your car would have come new with hydraulic lifters but it is quite possible that it now has mechanical lifters and that they need adjusting. After you get that under your belt, it would be a good idea to do a compression test and see what you have.

ghoenshell

I have a '53 Cavalier, same as your car, just one year newer. I'm chiming in because many of the symptoms and struggles your describing are the same as ones I had with my car.

Valves ended up being my issue, and as Ross mentioned, your symptoms also describe a valve issue.

While my car was idling I was able to pull plug wires one at a time to see what happened. When I got to #4 pulling the plug wire made no difference to how the car ran, that cylinder was basically dead because of a bad exhaust valve. #6 exhaust was also bad.

A compression test will give you a good idea of what's going on, and a leak down test will also provide some good information.

If it is valves, and yours are mechanical, maybe they they just need adjustment.

I just did a valve job, first time doing that, and my car starts and runs better than ever.

I don't think a worn distributor is your issue, but I did rebuild mine because I would wiggle the shaft back and forth quite a bit. The Delcos have a grease cup that is easy to miss, so the top bushing sometimes wears out prematurely.

Good luck and let us know how it goes!

Thank you all for your suggestions and insight. As I follow each of your suggestions, I will report back with the results.

Quote:

Sounds good. You'll get it sorted out, and learn lots about your car along the way!

I was able to take a look last night and did confirm that the lifters are Hydraulic. Also no arching or glowing from the plug wires, so it sounds like its time for a compression test this weekend.

I was able to do a compression test over the weekend.
I performed the test twice. Once when the engine was cold and the other time after the engine had warmed up by driving it. I kept the cranking duration roughly the same length of time on each cylinder.
Here are the results.
Cold:
1 = 95
2 = 50
3 = 65
4 = 25
5 = 45
6 = 45
7 = 60
8 = 25

Hot:
1 = 110
2 = 120
3 = 110
4 = 115
5 = 110
6 = 70
7 = 120
8 = 110

Obviously cylinder 6 is an issue. How are the other pressures looking? Is 110-120 PSI signs of good compression, or is it low?

Plan of investigation is to remove the valve cover and watch the #6 cylinder valves to see if they are operating and the lifters are squirting oil.
A: if the lifter isn't squirting oil, then that is at least part of the problem.
B: if one of the valves isn't moving (stuck) then figure out why (potential carbon buildup, valve guide issues?)
C: Check clearance with feeler gauges between valve and lifter.
D: If all else fails, I guess pulling the head is the next option? Is it worth using some additive to help lubricate the valves either in the oil or in the fuel? Is there a chance to put a borescope or camera down the spark plug hole?

-Grady