I’m 100% certain the cam timing is set correctly and it’s rare I’m that certain about anything with this truck. But it was a very real concern for me so I made certain while it was all right there in front of me. I figure I’m 50/50 on the distributor so I’ll start there.
Are you assuming that the cam sprocket was on the key, and the key was in the cam,not sheared, and that the keyway was machined correctly?
That camkey is only there to ballpark the cam timing. Once you have torqued that bolt down, It wouldn't need to be there at all.
But if the bolt is not properly torqued, then is is easily possible for that key to be beat up and this will allow the cam to run retarded. Eventually the key could shear, and the engine stops running.
A retarded cam causes a decrease in low-speed torque, and retarded idle-timing,and a lazy engine. When it gets lazy, the vacuum is reduced, and airspeed thru the carb falls off, leading to hesitations.
So then you check the ignition timing, see that it is retarded, and retime it.
Now not only is the cam-timing wrong to where the piston is, but the new timing is too early and drives the piston back down the hole backwards; so lazy, lazy it is; and timing advance with rpm, lights the fire before the intake valve is closed, and she backfires under load.
I'm not saying this is your problem.
What I am saying is that if it is, you could be spending many many hours chasing your tail around in circles, and throwing parts at it with no results................
What I am also saying is that if your truck showed up at my shop; the first thing I would do is check that pick-up polarity, and if that is ok, then
the second thing I would do is check the cam timing. I get paid by the hour, and people expect results. And in your case, knowing that you have already thrown a D,a carb and a valve job at it, and the very low compression numbers. You could not talk me out of checking the cam timing.
I would send you away first; and I'm not kidding. If I had to, I would offer a free check , with the proviso that if I'm right, then you pay double. Not only do I fix stuff, but I teach lessons. I am not a throw parts at the problem kindo guy, to see what sticks. That is why people used to come several hours one way to whatever shop I was calling home.
And yes, I have told customers to piss-off. With endorsement from my employer. In one hour or less, I can prove the cam timing is close enough to not be the problem.... or it is the problem. Now I can move on.
But if I don't check it, and I spend three hours checking every thing else, and if it should happen that I find nothing; then I have to back to the basics and do the cam-timing check.
If it should then be that is where the problem lies, just try charging the customer for those first three hours.... nevermind the new D I threw at it, or the new fuelpump, the wires and ignition parts, and the different carb. The customers in my neighborhood are mostly farmers, and they ain't stupid. They are gonna hold me accountable.
So i will have to remove all the parts I mistakenly threw at it, costing my boss more time, and now He is not happy. And then all thatcht falls on me. Ain't happening I got no time for that.
I was usually backed up several weeks for work, so if the customer don't play ball, then piss-off. Take yur stuff down the road to that new shop,Slippery John's Place, I hear he's desperate for work,lol.
What I am saying, "charm",
is after the polarity test, just be ready to come back to cam-timing. Your 115psi, after a valve job. is pointing straight to a late-closing intake, or
a high-elevation location.
And I checked; Everett is close to sealevel, ~100 to 400 ft.
