QuestionI have a 69 c-10 pickup. The engine is a Marshall rebuilt 4 bolt 350 with about 35K to 40K easy miles on it. I think it is a newer year as it uses the small diameter sparkplugs than what was in it when I put the engine in about 5 years ago.
It developed in what seemed to be a few days a backfire that got progressively worse to the point that the engine will bog down and die.
The backfire is relativley predictable, that is it sounds as if it happens in the same interval. I have gotten the engine to idle by turning up the idle screw. But if I put it in gear (automatic) it bogs down and dies.
I have checked the timing, replaced the distributer cap and rotor (HEI Accell)replaced the plugs, checked for vacuum leaks, put a compression gauge on the cylinders. The lowest was 120 there were two at about 143 or so and the rest were in the 130 range.
At times I think it is the carb as it seems to run very rich, and some of the gasket ends (that stick out beyond the carb body) are wet. I know that the valve covers are leaking a little, and I am not positive, but there could be a leak at the header to the manifold.
Someone told me that it could be a worn cam or stuck valve, but wouldn't that show up in the compression test? I know the 120 is a little low, but would it cause all of this?
Any ideas on where to start would be greatly appreciated. I am about to put the truck up for sale and would like to have it running without spending a ton of money buying and installing parts chasing down the problem.
Thanks again
Art
AnswerHi Art, The camshaft could be the problem. I would remove the valve covers and check the lift on all the rockers. This will tell you if the lobe has worn off the cam. This is the easiest thing to do first.
Hope this helps
Have a Great Day Mark
