305 issues

[355shortbed]

i just bought a 84 c10 stepside with a 305 w 3sp automatic. the truck use to be 3 on the tree. when i first got it it had all factory smog on it including manifolds intake q-jet carb. when u put it under a slight load it would pop through the carburetor, with the air cleaner off i could see a little fuel coming up through the choke horn. so i bought a new 600 cfm squarebore summit carb. new intake manifold, set of headers. new plugs, wires, cap, rotor, vacum advance, mechanical advance weights and springs. and its still doing it. tomarrow will be doing a compression test and possibly adjust the valves. but im kind of stumped on it. any suggestions would be appreciated. im thinking possibilities could be bad lifter, burnt valve, cracked head? the person i bought it off of said maybe a valve isnt adjusted right and causing it not open far enough, but wouldnt u hear it ticking and theres no ticking sound and plus it would be idleing ruff and it idles smooth with no misses

[Captkaos]

I personally would put the Q-jet back on it.
It sounds like a timing problem, I would check the valves.

[jimbo]

I see you have gone through your distributor.  Where is your timing?  I second checking for a valve issue.

[Josh454]

It's probably because your cylinders are too small. 

   Just kidding.  I would first get a handle on the basic engine health by doing a compression and leakdown test.  From there I would suspect the valvetrain.  Sticking valve, burnt valve, worn guide or a weak/broken valve spring.

Can you duplicate the concern by power braking?  I would try to see if you can isolate it down to one cylinder.

[355shortbed]

i tried to power brake it and it didnt pop n crack. under a slight load it starts to pop out the carb, like a hill or revving it up. i did compression test and all cylinders were 150psi.  a local engine builder says i probly have a lobe wearing down on the cam in the 305.  im looking to rebuild a 350, a simple bottom end nothing crazy. a set of alum heads and a nice bumpstick.  i am going to be depending on this truck to be driven daily so while i have the money i want to put a reliable, fresh engine in it. so im ditching the 305 because whats the since in puting money in a 305 when more horsepower can be had for the same money plus 45 more cubes!

[joesgarage71]

Yea your cam is shot. ie popping up through the carb