I have a 305 in a Toyota pickup and am having a major issue with it.

Engine specs:

305
Edelbrock Intake mani
Accel HEI distributor
Headers
MSD Plug Wires (brand new)
NGK Spark plugs, didnt touch gap (brand new)

When you hit the gas you get a nasty backfire through the carb, it idles perfectly fine, it seems to be on a intake stroke through one piston (only fires through one side of the carb). Did a compression test thinking that it was a burnt valve, and its 100-110 in all 8 cylinders. Noticed the spark plugs had quite a bit of unburnt fuel, so I thought maybe it was the carb, swapped out from Quadrajet to a Edelbrock Street carb. Same thing, runs alot better with the Edelbrock, but idles perfect till you hit the gas and pop-pop-pop out the carb. Had a look at the timing advance springs and it seems fine, firing order is fine (quadruple checked that).

Any ideas? I would like to avoid ripping down the engine if possible.

flat cam

X2 on flat cam most likely exhaust lobe on #6

Is the #6 common or something? What would cause a flat cam?

lack of oil is all i know of. BBC's had the problem, and ol farts say crank your idle up until a new engine is full broken in.

Ummm...have you checked your timing? I would start there for I rip out the cam.
Kinda off topic, but there is a oiling kit made for big block chevy motors to keep the cam from having premature lobe wear.
I forget who makes the oil line kit, but if I can find it, I will post it.

if its backfiring through the intake at speed, its a flat cam. dont bother changing the timing. its done. the cam is toast. the longer you fight it, the worse the bearings will be, because metal is flaking off the cam, and going through the oil pump, bearings and destroying the engine.

when you break in a flat tappet camshaft you must immediately (UPON STARTING) run the engine at 2000-3000 rpm *most people like about 2500* for about 30 minutes. get it RIGHT up to speed, or you will be doing it all again. no tuneup blips, no idle check, just get it to speed. You should try to find some kind of engine oil supplement to use to break in the cam, as the first few moments of a cams life is critical. the wrong lube, or not enough of the right ingredients in the lube will kill a camshaft.

If you didnt know, there has been a major shift in oils in the last 2 years. Most all oils you buy off the shelf do not have the phosphorous or zinc in them that is required to keep the lifters from failing. why? because we now have roller cams, and the gov't wants tighter emissions controls. so they knock out the phosphorous and zinc.

Those two additives in the oil keep the cam from dying.

fix it, or itll fix your wallet.