backfiring, need help!

Just finished the carb conversion on my 91 GT.. Got initial timing set at 10*..Set idle & fuel mixture, float level & fuel pressure is at 5psi.. I'll probably bring it up to 6psi though..

Anyway, when I have the vacuum advance plugged on the distributor, the motor runs great.. If I connect the vacuum advance to the timed port on the carb, when i give it gas, it bogs & backfires.. I can very slowly bring the revs upto 1500rpm, but thats it.. then it starts to bog..If I give it gas quickly, it backfires throught the exhaust..

I dont get it... Could it be a bad vac advance mechanism? bad distributor?? I am using a used distributor off of an '85 GT with the steel gear for roller cam..

I've been told this dizzy has mechanical advance built in, so I should be ok to run it w/out the vacuum advance.. just set the total timing to 32*, and it should be ok..Any truth to this?

But I would much rather correct the problem, than "band-aid" it..

This ever happen to anyone? I was thinking about just getting a reman dizzy.. They are $50.. drop it in and see what happens..

Oher specs on the car are:
Stock 91 long block..
Performer 289 INtake
Holley 600 carb
MSD 6A & Blaster 2 Coil, 9mm wires, new plugs
Holley Blue pump, mallory bypass regulator..-6an braided hose throughout.
Stock '85 dizzy from a Manual tranny GT w/steel gear.

Any info appreciated..

Joe

but why is it happening?? is it b/c there is no ecm controlling it & between the mech adv built in & the vac adv its too much?? or is the vac adv can faulty??

I checked my mechanical advacne today.. The weights in the distributor are 13L & 18L, its on the 18 side..

So that means I have 36deg of Mechanical advance, plus the 10* initial, 46 total which is kinda high..

I tried to flip the weight so I would get a lower mech advance and give me more room to play, but it seems like you need a special puller to remove it from the shaft..

So I left it as is, and lowered my initial timing to 8*.. So now I've got 44* total.. I could go down to 6*, but left it at 8*..

Reconnected vac adv to timed port, same thing.. I'll try the manifold vacuum port tomorrow.. But i dont think it'll help.. I think the car wont even start then if it is bogging down with the timed port..

I made sure everything was nice and tight.. INtake bolts, carb bolts, header bolts.. So I dont know from where I would be getting a vaccum leak..

I'd like to have it working properly, but the motor feels pretty good without it.. I guess I will ultimatly have to just wait till i get it back on the road to see how much of an affect it has on the driveability & mpg..

If i had too much total timing, could that cause the problems when I hook up the vac advance?? Or would it mainly be due to a vaccum leak? Or maybe the advance canister itself is no good..

ttt