Help!! Backfiring after re-doing top end

[skiwesser]

Ok guys here goes,

I had stock E7's milled .035 and ported exhaust (removed therm.

bumps) port matched stock intake as well as adding 1.7 RR's.

I also blocked off EGR in intake and removed all smog equip.

blocked off passages on back of heads.I also added fuel press

reg. & guage.

I have the timing set at 10*,fuel press. at 39lbs & it is backfiring

a little at idle & at part throttle, not so much at WOT?? I can't

figure this out, its not loud(right in the header) no detonation

detected. It's a 88 GT speed density, stock cam.Why would

unburned fuel make it out of the exhaust valve?? too much fuel

press??I also added syn. oil & now it smokes a lot (shortblock

has a lot of miles but i couldn't afford re-build) I almost think the

syn oil is leaking past the o-ring style exhaust valve stem seals

can you get umbrella seals for the exhaust valves? will intake

seals work?

Thanks Guys!!