Need help with engine problem

[Lynn]

I would make sure it is timed properly before swapping out parts.... even if you are going to swap the exhaust eventually.

I can promise you that you can use a dial back timing light. Once you see it hooked up and figure it out, you will see how simple it is. You really don't need a dial back light. Assuming you have an 8 inch damper, and assuming the single mark is Zero, 10 decrees advanced will be 1.44 inches from the single mark.

[SuperNovaSS]

It sounds like the car was running fine before the exhaust and clutch job. Is that right? If that is the case, I would back track from there. Was the distributor moved or removed when the clutch was done? Ground not hooked back up? Pinched wire as mentioned earlier? Battery not disconnected during welding which would have fried the module? Ignition modules are cheap and an easy swap. I wouldn't start thinking about internal issues like valve clearance if the car was running well before the exhaust and clutch job. If the distributor was not messed with during the job, I would not be worried about ignition timing.


Jason

[drdave69]

Once I get the time to get back at it I will check TDC. As far as I know the distributor was not messed with when the clutch was changed and there has been no welding done on the car. I will also check for any pinched wires. I know that timing and vacuum leaks can cause the fire in the carb so I am leaning toward a timing issue since I could not detect a vacuum leak.

[drdave69]

I looked for any pinched wires and did not find any. I took the distributor cap off and removed the #1 plug. Bumped the engine around and the rotor correctly points to the #1 plug on compression stroke. I then examined the dampener again and noticed faint lines and numbers on it. Couldn't see them previously with the crusty surface so I sanded it a little and marked the 10 deg BTDC with white paint. It was aligned at about the 12 deg mark so I put everything back together and checked it with the timing light after letting it warm up (wouldn't stay running otherwise). I adjusted it to the 10 deg. Using the electronic timing light I was able to switch it RPM and noticed that it was idling at around 750 rpm but the tach was at 1000 rpm. I assume the tach is off. It will still "run on" when I turn it off and still isn't running very well.

My next plan is to put it on my lift and change the oil (it is due) then swap the 3" side pipes back onto it.

[VintageMusclecar]

Dave;

Have you made any adjustments to the carb yet?--where are the idle mixture adjustment screws currently set at?

Have you put a vacuum gauge on it? If so, how much vacuum is there at idle?

Eric

[SuperNovaSS]

Is the tach still a factory mechanical tach or is it electronic? If it is electronic, I would try disconnecting it. Also, I believe you said this was GM HEI. If so, as I said before, I would swap the module or at least have it tested. Modules, coils, and pickups for HEI go out from time to time and can cause the issues you are describing.


Jason

[drdave69]

Eric, I adjusted the mixture screws to achieve the highest vacuum at around 13 - 14 inches. I printed an instruction sheet on how to set the choke and fast idle cam. I'll get to that the next time I work on it.

I put the 3" side pipes back on it and drove it a little while this evening. While it will idle when warmed up it still doesn't want to when cooled down a little and it still has a little "run on/dieseling" when turned off. I may play with the timing in 2 deg increments to see if it helps any.

Jason, the tach is the original (I assume) and it appears to be mechanical. The 502 has the factory HEI. I have replaced the coil but not the module(s) in the body. Is there a way to test it/them? As you stated would a bad module(s) cause the poor running characteristics or would it cease to run at all?

Thanks for all the help guys. Hopefully I can figure this out without having to find somewhere to take it.

[napa68]

The module controls dwell. Bad modules, while often just stop running, can cause a variety of other issues. They also too, can be heat related (heat soak)

Tim

[SuperNovaSS]

Many auto parts stores have factory ignition module testers. I used to work at NAPA and we had one. Yes, a bad module could definitely cause the issues you are describing and the symptoms can vary with temperature and humidity. The GM HEI one is very common and inexpensive. Any auto parts store should have one. Install is very quick and easy.


Jason

[drdave69]

Made a little progress over the weekend. Based upon some instructions located on the internet I checked the hei coil and it checks out as ok. I then focused on the carb since it doesn't want to start when cold. I adjusted the electric choke a little and noticed that the fast idle cam was not functioning. I adjusted it and now it starts and idles high when cold as it should. Seems to run better now that these adjustments have been made and it has the 3" side pipes back on it.