white smoke start up and hesitation on aceleration off idle . recent purchase 1987 firebird 305 carb original engine original carb application with 65000miles.carb recently replaced found when engine shut off no gas looking in bowl carb from excellerator pump. took carb apart found lip seal to still be good in quadrajet . reassembled carb new seal replaced fuel pump checked choke and varied timing . no change ? this carb is power controled by ecm? seems to be dumping alot of gas start up? when replacing pump found excessive volume coming from return line which goes to tank ? at pump ? had large vacume opening filler cap of vehical , replaced still vacume ? replacing pump and timing helped hesitation but still there start up smoke intermitent please open to sugestions im old school qjet guy when no pump shot check ball below pump not seated , not same in this qjet???

 

White, or bluish? White is coolant, blue is oil, black is excessive fuel. SBC smoke at start-up 90% of the time is hardened/cracked valve stem seals.

The primaries mixture is controlled by the ECM via the mixture control solenoid at idle, cruise, and light power. After about 3/4 throttle it's open loop. The choke operates just like a non-computer electric choke q-jet.

If you are getting a lot of fuel at start-up, you might have leaking well plugs, just like non-computer q-jets.

Not sure what you're saying there. Vacuum at the gas cap is a vapor canister problem, not a fuel return problem.

The fuel pump will not/can not affect/cause smoke at start-up, assuming the pump isn't causing flooding which remains for the next start-up.

The accelerator pump design is identical to non-computer q-jets.

 

hi thanx for reply i think ill be doing heads after holiday someday its blue in color somedays nothing ive done spring compression on pontiacs to remove keepers before on engine found over years easier to pull heads do it on work bench with valve spring tool . thinking about doing this one on engine only 65,000 miles runs excellent . any suggestions on spring compressor on engine good easy to use tool where i can buy it the one i had years ago'' kd'' wasnt what it was cracked up to be! thanks canister sounds right just being interminent smoke thru a curve when pontiacs scraper oring seals cracked they smoke alot all the time!

 

hi a update went to start car had to crank 8-10 times looked at excellerator shot completely dry, engine started before with out pumping excel pump. zero gas in carb today , well plugs i understand draining pump shot but not carb?? vacume canister cause problems effecting timing lost vacume to advance but sucking down primed system??? remember when i replaced pump i had heavy volume fuel coming out line returning to tank even primed fuel pump and carb up ! ill get canster but still think ive got a cstrange problem here any suggestions please?????

 

1) Leaking well plugs CAN drain the entire carb bowl leaving it dry.

2) Your distributor should be electronically controlled and should NOT have a vacuum canister controlling advance. The advance is controlled by the ECM through the four wire connector to rear of dist.

3) Your vehicle should be equipped with an in-tank, helper pump. Key-on should engage this pump and elminate any need to 'prime' the mechanical pump on the block. You can check the function of this pump by jumping the relay, driver side firewall. The relay will look similar to the fan relay with a four wire connector. Should be able to hear it run or pull the rubber feed line off and verify it's pumping. It's pretty weak though and a pressure guage on it won't read much. It's purpose is to prime and prevent vapor lock.

4) If you suspect a problem with the vapor system disconnect it and plug the ports temporarily. See how it runs without it. Just leave the top bowl vent connected so the carb can breathe.

 

think im going after carb well plugs but this is original carb eng not f.i. thought mechanical pump only?? are u positive of electrical pump in tank?

 

For '87, YES, except for some export models. You can easily verify the pump is there by the two-wire oil pressure switch that will be tee'd off the one-wire oil pressure guage sender near distributor, off the china wall.