i have a 68 with a 302 auto. it runs very rough at idle and it does seem to get better when you turn the distributor but i dont think that's the problem. when i pulled the wires for cylinders 5 and 8 i noticed no difference at all in the idle. i replaced all of the plugs and those two wires with no change. any ideas would be appreciated.

 

If you pulled a plug and hear no difference its most likelya fouled sparkplug. Change the plugs and your problem is fixed ... its not your wires or you would have gotten the $hit shocked outta you .

-Hawkins

 

i thought it was the plugs too, but i replaced all of them and still no difference. i am wondering if it could be a misadjusted rocker maybe

 

If you can still pull them two wires and hear no difference, id change them two out regardless if i just replaced them. The reason im telling you this is because i had the same problem. I replaced all the plugs, then noticed a foul plug, changed it AGAIN, and it fixed my problem. What kind of plugs are you using? Gap'd correctly ?

You mentioned earlier that you adjusted the timing... before or after you changed the plugs? Whats your initial and mechanical? Id replace the twofaulty plugs again and adjust your timing before anything else.

Keep us posted.
-hawkins

 

Check to make sure the vaccuum advance on your distributor. Pinch the vacuum line when the engine is running and see if that changes your idle or if the car stalls. If nothing changes, that's your problem.

 

Dead appearing cylinders are hard to troubleshoot. Since it's 5 and8 (opposite ends of the head), a blown head gasket between them is probably not the cause. It's either poor spark,compression or lack of fuel. To check for lack of fuel, look for any obvious vac leak. I've seen bad/misadjusted carbs and leaking power brake boosters do this too. Pull the plugs from the entire engine and do a compression check. You want all of the cyls to be within roughly 10% of each other. for examplesay 162-180 psi as a ball park I'll bet 5 and 8 are low and its probably due to a burnt valves. For spark, look at the cap to make sure theres no carbon arcing ( it'll be obvious), spark plugs are gapped at .035, and the plug wire is good. (you said these last 2 steps were already done).
good hunting