Fletchmo72

My '72 Cutlass 350 with rebuilt (by PO) quadrajet has always run very well--smooth. But during a long drive on a hot day I was having issues related to over-heated fuel in the carb (I do not have a fuel return line). To fix this I installed a 1" plastic/nylon spacer to prevent heat transfer. Before reinstalling the carb I turned it upside down and noticed carbon build up in the narrow, u-shaped channel that runs between the idle mixture screws in the base plate. I scrapped this clean and blasted it with carb cleaner. Now my idle is terrible; above 1,000 rpm everything is good--as it was before. I've tried removing the idle screws and using carb cleaner through the openings. Didn't help. Wondering if the idle tubes are clogged and whether I can clean them, or should I just replace them.

m371961

I would check for a vacuum leak at the base gaskets first.

oldcutlass

Did you readjust the the A/F mixture screws?

Gary M

x2. If you scraped stuff off but did not put a new gasket on or for some reason the new gasket did not seal that may be it. Turning it upside down may be part of it too.

Fletchmo72

Sprayed carb cleaner around the base while running, no increase in rpm.
Mixture screws need to be opened beyond normal--about 4-1/2 turns to get it to idle.
Installed new gaskets when I installed the spacer.

Sugar Bear

Did you match the gaskets? Incorrect gaskets can block needed vacuum ports.

Try revving the engine and forcing the choke plate closed by hand until it almost stalls, open the plate and let it clear the rich mixture, repeat a few times. Be careful of backfire flames.

Pinch the fuel pump supply hose closed until it runs out of fuel and then release the pinch and crank it to start. This flushes the needle and seat clean if something is stuck on them. Blow compressed air through the bleeds just behind the choke plate surround wall next to the air cleaner stud.

Lastly, take the top off the carb. Sediment may have moved from the bottom of the fuel bowl and is blocking a passage.

Good luck and keep us posted!!!

Fletchmo72

Thanks for the tips! Unfortunately, nothing has worked so far. Haven't pulled the carb yet, as I'm waiting for a gasket kit to arrive. As I was working, I noticed a slight leak around the body of the fuel pump. Replaced the pump and rubber fuel line, including the small 3" piece along the frame behind the right front wheel. Didn't help my idle problem, but at least I averted a future break down! Hoping my carb rebuild kit will solve my issues. I'll post what I eventually find out.

oldcutlass

Look into the carb while its idling and see if there is fuel dribbling.