[kevin d]

Hey folks, a buddy of mine just bought a 72 chevelle, 350, 2 bbl, headers, th350. The car runs really hot and fires through the carb when trying to get it above idle. He said that when he bought it the previous owner had to turn the distributor to get it to run. The guy called two mechanics who never looked at it but told him he needed a new cam and they would do it for $700.00! I think his timing might be way off. Does this sound right? I guess I would check that before putting in a new cam. Are these bad cam symptoms? thanks,
kevin d

 

[tom wurm]

Kevin, some years back I purchased an old Ford truck which had the same type of problem. The timing gears and chain were so worn that the crank could be turned 35 degrees before the cam would start to turn. A set of new timing gears and chain fixed the problem. Remember though this was only an old work truck for me and I was not concerned with having a nice vehicle. This was the minimum that I had to do to get the truck to run, but I would suspect that if the timing gear and chain were worn so badly that there were probably a lot of other things in that engine that also needed attention. Good luck.

 

[Bob M]

The mechanics probably assumed that one or more exhaust lobes are flat on the camshaft. I've had this happen before and the car will backfire through the carb when it is revved up. After the plug fires the mixture, the gas can't get out through the exhaust valve because the lobe on the camshaft is flat. When the intake valve opens on the next cylcle, the gas goes out the intake and back through the carb. The mechanics should not make this assumption without looking at the car. There are a couple of things to check for. First, make absolutely certain that the spark plug wires are installed correctly in the proper sequence and that spark from one wire is not jumping to another wire.
Try to seperate them as much as possible and try to keep them from running parallel to each other if possible. Start the car at night and look for arcs jumping from plug wires. Second, try replacing the distributor cap. Worn and fouled distributor caps can allow the spark to jump around inside the cap and fire the wrong plug. If a plug for a cylinder fires when the intake valve is open you will get a backfire. Also, verify that the distributor is timed properly.

 

[COPO]

One more thing that will cause this is worn points and a bad condensor, if your still running them. It happened to me last year on a 396/375 car I worked on.

Mark