High end miss - need help

[Botietruck]

My son has a 71 truck with a 350 engine/th400 trans. A couple of weeks ago, the truck acquired a high end miss. Basically, either at idle or on the interstate, as long as he was barely on the gas the engine would run smoothly (even if he goose it while in park. Whenever he would step on the gas, either at low or high speeds, the truck started vibrating. It progressed into a high end miss eventually. Now it's at the point to where at idle it runs moderately smooth and if he gooses it while it's in park it will pop and backfire. If he drives it he can barely get it up to speed. Any ideas from anybody? Already replaced spark plugs. He had intended on installing a Holley so he went ahead and took advantage of the situation. No change. Vacuum advance? Timing issue? Valves? Any thoughts or help would be greatly appreciated.

[pumpkin]

If the ignition system is all good, cap, rotor, wires, points if it has them, then I'ld look at the valve train. Broken valve spring, bent pushrod, flat cam lobe, are some possibilities.

[rage'nrat638]

if it's got points..change them, could be alot of things. a complete tune-up would be in order. cap, wires, points, timing.

a level of integrity needs to be established..

how many miles on this thing..timing chain might be a issue.

let us know, your pal mark

[Botietruck]

Well, we found the culprit. Pulled the timing cover Thursday night & the timing chain was shot. The cam gear teeth were as sharp as a razor and the timing chain was sitting on top of the camshaft sprocket teeth. Replaced the oil pan gasket, new timing chain & gears and finished it up last night at 11:30 Engine fired right up and runs great & very quiet now...no rattle in the front cover area. BTW, we did a compression check and all cylinders were running 145 except for 5 & 7, they were in the 135 range.
Thanks for the advice from everyone!