Cold Start sputtering\w fumes

[joseph.signore]

My 1991 mercruiser 350 magnum with a 4 barrel quadrjet carburetor started sputtering and lightly smoking (white fumes) only when the engine is started cold. The motor seems to be loaded up and clears and runs fine after I race the throttle or a few minutes of warm up. I?ve cleaned the air cleaner, PVC and carburetor and see no problems with choke?its fully closed when cold, and open fully when the engine is warm. Any help would be appreciated.

 

[1ruralmailman]

Re: Cold Start sputtering\w fumes

problem is with the carb. she is leaking a little drip of fuel when she sits.time for a rebuild. dont know for sure on this one but on some i have seen on trucks there are little metal plugs inside them, that are there when they machine them,that is where the leak is.used to be able to purchase a fix it kit for them at napa,but doubt they are still available since all vehicles are now efi.have seen guys get adventursome and plug this leaking with jb weld,i have never had any luck with that,but i know some that have.

good luck

 

[Lou C]

Re: Cold Start sputtering\w fumes

There is a vaccum operated valve that is supposed to pull the choke plate open a fraction of an inch to give the engine enough air when the choke is on, is that still working? After the engine starts you should see the plate open slightly. The official name of it is the choke vaccum break...if it doesn't work your cold start mixture will be too rich.

 

[airdvr1227]

Re: Cold Start sputtering\w fumes

Anyone else think running rich would make for black fumes? White fumes suggests water somewhere to me.

 

[Aloysius]

Re: Cold Start sputtering\w fumes

Excellent and accurate advice so far. The smoke is actually blue from excess gasoline washing oil off the cylinder walls.

Time for someone who knows what they're doing to rebuild/repair the carb. I strongly advise against buying a "rebuilt" carb..keep what ya got.

 

[joseph.signore]

Re: Cold Start sputtering\w fumes

Thank you all so much for the great advice? I found my vacuum breaker (white plastic valve) was broken off the bracket. Although, it still holds a vacuum it?s unable to pull the attached lever. I had never checked this because I thought it controlled the secondaries. I?ve also noticed since this problem started the boat has been using more fuel. Maybe it?s time for the rebuild you guys suggested. Any idea where I can find this plastic vacuum breaker? Again, many thanks for all of your comments and help.

 

[Aloysius]

Re: Cold Start sputtering\w fumes

The choke pulloff is common to all quadrajets..a professional auto parts house may be able to help you. It's held on with a clip..did it just come unclipped??

 

[joseph.signore]

Re: Cold Start sputtering\w fumes

Thanks! It cracked and split on the back where it connects to the bracket, but did not affect the can/diaphragm, its still holding the vacuum pressure pulling its self off the bracket.

 

[NHGuy]

Re: Cold Start sputtering\w fumes

That is great, it's easy to understand and to fix.
You probably understand this now, but when the engine produces vacuum the diaphragm slightly pulls off the choke so the carb can get enough air to increase engine speed. Just fix the pull-off before you go ripping into the carburetor. Once that is done recheck engine behavior.
Oh and you might want to take a whiff of the motor oil, if it smells gassy change it. Or just change the oil to be proactive and smart.

 

[Silvertip]

Re: Cold Start sputtering\w fumes

Probably your local Chevy dealer. It my be called a "choke pull-off" in their parts lists. They will need engine year but may have to look at older models since by 1991 everything in the GM line was fuel iinjected except perhaps some trucks. Try to talk with a parts guy that is older then 20 as these young bucks wouldn't know a carburetor if they tripped over one. Even NAPA may have them.

 

[joseph.signore]

Re: Cold Start sputtering\w fumes

Thanks for the additional help. I?m going to try NAPA tomorrow, if not, I think I found it on line for $7.95 at http://www.carburetion.com/quadrajet.asp and I?m definitely going to change the oil?great advice?This forum rules!!!