sbc 305 need help!

Hey guys ive got a major problem I believe and need some ideas on the cause. I have a sbc 305. nothing fancy, mild lift hydrolic cam. ive ran this cam and top end on a 355 with no problems. What I am down to now is I have to be at about 50degrees advance for the engine to run. sounds awesome, idles great, revs good without load but severe lack of power on track. ive never ran a 305 before so I wrote it off to that. But if I crank back the timing to about 40 the idle goes south and I get a backfire thru the carb. we rebuilt the carb, I know my distributor is good, plugs good, proper fireing order all the basics have been checked and double checked and correct. is it possible I have the cam itself off a notch and still be able to make it run despite not setup correctly?? any ideas iam lost.. thanks in advance.. nick

Sounds like the cam is installed incorrectly.

Which timing cover and balancer are you using? The 305 cover and balancer have the timing marks at 12 o clock if you use a 350 cover and the small 305 balancer, the timing will be at least 45 degrees out.

What type heads are you running might be lacking compression. You said 355 top end what CCS heads? What piston?

Like Racer Roy said, the timing lines are in different places 305 vs 350. A lot of 305 balancers have the timing mark 10 degrees before the keyway on the crank. This may account for your timing issues, assuming that the cam is installed correctly.