Weak engine?
 

I have 72 c10 with a factory 402 big block The engine is supposed to be a factory rebuilt engine,I have no reason to believe otherwise I actually found a certificate under the seat stating that it is.I can tell the engine has been apart by the blue gaskets.It idles really rough like it has a healthy cam in it but it seems gutless.A 4 cylinder would walk all over it.I took the distributor apart and cleaned it and replaced the advance weights and put a new vacuum advance on it didn't help much.Did a compression check all around 150 on a cold engine I no my bad but those manifolds burn the crap out of your fingers.I just can't figure out why this engine has no power.Like I said the engine sounds mean like it has a big cam in it.

Re: Weak engine?
 

Dist. 180 degrees out? I've seen that happen before. Hot manifolds could mean it's way too advanced.

Re: Weak engine?
 

Is the initial timing right. It should be about 12 degrees BTDC. Sometimes the Marks are wrong. Try advanceing it & see what happens. It could be a bad vacuum leak. The carb base may not match the manifold. The secondary throttle valves may not be closeing all the way. Check for a clogged up exhaust system. If everything checks out it may be like Jay says. The timing chain may be off a tooth. If it was more then that it would not run at all.