Need help with engine problem

[drdave69]

My ZZ502 is still not running very well after a few attempts to fix it. I drained the fuel and had the carb rebuilt (by Eric, thanks) and installed new: plugs, plug wires, distributor cap/rotor and new coil (HEI). The engine still doesn't want to start and run very well. It will NOT idle below 1000 rpms. I checked the timing and it appears to be correct since there is only a single indicator line on the timing marker and it was on it at 1000 rpms. I checked the intake and carb with starting fluid to see if there is a vacuum leak and did not notice any increase in rpm.

Is there something else I can look at? Could the timing chain be stretched? Is there a valve train issue?

[earntaz]

Have you tried a 12V jumper wire from the battery to the HEI? This will bypass all possible connection issues in the ignition.
Have you changed the valvetrain at all? If so, is the valve adjustment too tight?
Is the harmonic balancer stock? If timing cannot be set correctly -- engine will be hard to start will not idle. Possibly remove all the plugs and check true TDC at #1.

TAZ

[seventieshow]

"a single indicator line on the timing marker"...Is the line TDC, 8 degrees, 12 degrees? ...should not be TDC at 1000 RPM. Or any RPM. Probably more like 10 degrees at 1000 RPM.

"is the valve adjustment too tight?" Sort of sounds like this problem. As TAZ said, confirm TDC and timing marks and check valve adjustment.

[earntaz]

After reading Don's remarks above -- something else just occurred to me. Check the advance mech in the distributor -- does it rotate freely? Sometimes the shaft binds up in an HEI ... they are good for that! TAZ

[drdave69]

I will try a 12v jumper to the hei after I double check tdc. As I stated, there is no degree indicators on the balancer or indicator. Just a single line. The engine is as it came from GM and I have not changed or adjusted anything. It just all of a sudden started running this bad after a new clutch and exhaust (went from 3" to 2-1/2" side pipes). I checked the advance mechanism in the hei and it is not binding. From what I have read the timing should be 10 deg and I assume that is what the single line indicator is for. I do not know what the valve adjustment specs are for this engine.

[seventieshow]

You could try driving it with the exhaust opened up, see if it makes a difference.

[seventieshow]

With this additional information, I would leave the valve train be. I get the impression it has a vacuum canister on the distributor but they (Chevrolet) want it plugged off and not used.
Are the 2.5 side pipes a full 2.5, I've always heard the factory pipes were restrictive.
Since you are there anyway, look and make sure nothing got pinched by the bell housing after the new clutch.

[Lynn]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: drdave69</div><div class="ubbcode-body"> From what I have read the timing should be 10 deg and I assume that is what the single line indicator is for. I do not know what the valve adjustment specs are for this engine. </div></div>

Other than Studebakers, I have never seen an engine with a single line that was anything other than to indicate tdc. Can someone with 502 experience shed some light on this? Did you get a spec sheet with the engine telling you where timing is set? Surely said spec sheet would tell you what the single line referenced. I am afraid you have zero initial advance. Guaranteed to run like it is tied to a tree. Do you have the distributor specs? Find out how much total advance (in crank degrees) is built into the distributor (not counting vac) and set the initial to give you a TOTAL OF 36. That should be good for starters. So... if you find the distributor has 28 degrees total cent. advance built in, set initial to 8 degrees. If it has 26 degrees built in, set initial to 10 degrees. Is this a GM crate motor? If so, I have a hard time believing you didn't get a spec sheet.

Is there a scale of any sort (i.e. one line on the damper, but a scale on the timing cover)? If not, and if you don't have a &quot;dial back&quot; timing light, you will need to approximate.

[seventieshow]

This link has a PDF that tells basic timing information.

http://www.chevrolet.com/performance...02-deluxe.html

[drdave69]

Thanks for all of the suggestions.
First off, I bought this car and engine combo as is and I was told that the engine was installed around 10 years ago. No paperwork was included. I have printed the install/engine specs from the GM Performance site for reference.

I plan to check where TDC is in relation to the timing mark when I get back to it. I am not well versed on how to use a dial back timing light so that may be above my pay grade.

If you think the exhaust is restricting it that much to cause this issue I can install the 3&quot; pipes back onto it (I had already planned to do this). I have already pulled them out of the attic to swap them out. I will also check for any pinched wires, etc. when I look into the exhaust.

One additional note: when I started it the other day it did not want to stay running until warm and it stalled when I backed it out. It was difficult to get it started again and puffed a little fire back thru the carb before I finally got it started after pressing the throttle down.