i wonder if im missing something on this carb?These quadrajets are the one year only with an auxiliary power piston . i rebuilt this carb that is original to my 76 cutlass supreme 455 last fall and did some testing and tuning before the weather went bad .The car ran really well with the exception of it smelling pretty rich.Fast forward to this week and as i did an oil change on the car the oil smelled real gassy. The only thing i changed in the carb was i went up 2 jet sizes from 68 to 70 . i thought the motor could easily handle that since we put large valve e- heads ,dual exhaust and a edelbrock performer and a little bigger cam .with all these engine changes the carb was in its original state and worked great with the exception of some high rpm gas starvation (at least what i figured).last night i pulled the carb and checked my float level double checked that the wells weren't leaking check my needle and seat everything inside is clean as a whistle.My question is can going up two jet sizes cause this richness?or am i missing something else ?

 

Did you change the fuel pump? Some fuel pumps put out way too much pressure vs spec, it has happened. What was the original application for the carb? What primary rods are in it? So it actually has the extra jet and rod? Not all 76 carbs had that feature. Two jet sizes is noticeable change. Go back to what it was and see, without a wideband, you are hit and miss.

 

X2 on fuel pump, it can be too much pressure output or a leaking diaphragm allowing raw gasoline into the crankcase.

Had there been several cold starts without full warmups lately that would cause an over rich situation? Are the tailpipes caked with soot?

Good luck!!!

 

this is the matching numbers carb that is on my 1976 cutlass supreme factory 455 motor turbo 400 trans and 256 posi .i have not changed my fuel pump and the tailpipes are sooty.I just finished putting the #68 jets back in.I won't be able to test drive for a while with 10 inches of snow coming. Ive read through the cliff ruggles book but it basically says avoid these auxiliary power piston carbs and never goes into the apt adjustment procedure.i won't mess with that until i better understand it.

 

While idling in park, use a flashlight and see if there is fuel dripping out of the primary nozzles. The throttle blades should be closed at idle (picture). Carb must be off & inverted to check. Larger cam may require softer power valve spring.