HELp! heavy missfire- runs horrible

[Myles]

Hi guys,

81 Malibu 355sbc started running like crap at the track. After tuning to eliminate hesitation, bigger nozzles amd 50cc pump, etc, it was fine.

Then noticed my timing was somehow move to 55deg at idle!
Maybe was moved when guys installed new stall..

Backed it off to normal , hesitation came back. Tried car anyway. After the burn out, car died. Then, and now, idleing and misfiring all day.

It only starts (and runs like crap) now if I advance the distributor all the way.

At track we checked vacuum, still 10-12 at idle. Tried my existing 750hp, a new rebuilt 650hp, another complete distributor, checked all closed vac ports, tested power to distributor,
Really started to pull my hair out.

Plugs always seemed fine, now theyre a little black, probably due to the bigger nozzles, playing around and trying to start it, partial flooding, etc. Other than plugs, I dont know what to do. Spark plug wires correct. Car motor chassis has lots of new good grounds.

Any tips, or has anyone gone through this?

Thanks
Myles

81 Malibu 355 9.5-1
Th350 5000 stall
4.56 spoil 28" slick
Holley mechanical 750hp
Stock nozzles back in, 28&32

Bat and fuel cell in trunk. All wiring and fuses test okay. Thanks!!

 

[pontiacgp]

timing chain jumped?

 

[bracketchev1221]

What balancer is on it? Make sure the ring didn't spin.

 

[Clone TIE Pilot]

Check for vacuum leaks.

 

[Tc77]

Plug wires, balancer, flat spot on cam . Timing jumped. Bad coil

 

[MrSony]

If the vacuum is the same, that pretty much eliminates a sheared lobe.
I'd say balancer slipped.