I have a 351 cleveland that has a 3/4 race cam in it with around 12.1 compression(yeah, i know thats high). It has started to run really crappy, and has exhaust backfires like crazy. Also when you hit the throttle it is very slow to return to idle. I have checked the throttle spring and made sure it is fine and everything is free. It just doesnt seem to idle properly, and when i hook up a vacuum gauge i get a reading of about 5 pounds, it is a steady reading, the needle doesnt move very much. I have played around with the timing, and messed around with the idle mixure. The last few times it has been started it seems to have gotten worse. Any ideas?
Thanks
Matt

 

Hi Matt,
Have you put a timing light on it ? It sounds like you may have it retarded too far.
How easily does it fire when you start it ?
Ron

 

180 off?

 

Thanks for the reply,
I have the MSD timing controller which allows me to adjust the timing 7 degrees both ways. I havent touched the timing in over a year and it was running great not to long ago, the problem is pretty recent. I was just outside and pulled out osme of the plugs and found them to be carbon fouled really badly. There is no way that these plugs could all be firing properly. I am going to get some new plugs tomorrow, and see what happens. I have a feeling i was runnig to rich, and to make it worse i only go cruising around town. I never really opened it up on the highway. I guess that the unburnt fuel is getting into my exhaust and igniting, causing a backfire. Do you think that my carbon fouled plugs will cause these symptoms?
Thanks
Matt

 

They could.I'd check your leads as well.Anything over 12-14k ohm resistance and you should throw them away.

 

Hello,
I replaced the plugs and that made no difference, even though the gaps on the old plugs ranged from .025 to .035, i have no idea why but thats how they were. I also disconnected the electirc choke and unpluged the wires to see if it was the choke, still no difference. Each time i rev the car it is very slow to return back to idle, it will stay at 1500 rpms for a few seconds then drop down.
Any Ideas?
Matt

 

hmm i would guess rich condition now is this only when warming up or all the time it could be a float adjustment or excessive fuel pressure or the change in temps could be effecting your mixture these are also things to consider cause my car has probs here cause it runs gr8 in summer but until i tune it for winter i have probs like this

 

It sounds like timing to me, too. How many degrees do you see at idle and at full advance?

Justin