Curing Quadrajet Carb Woes - Tech

Here Are Some Interesting 21st Century Fixes For Your 20th Century Rochester Carb.

Doug Marion Apr 27, 2011 0 Comment(s)
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Culprit: Ethanol? (Ethyl Alcohol)
Today's pump gas contains as much as 10-percent ethanol. It is a liquid compound made from simple sugars. Refined, it is an alcohol with the chemical structure CH3-CH2-OH. It is said to be 20 to 30-percent less efficient than gasoline. Nationwide, carburetor experts I know all agreed that in my instance, ethanol did not cause, and would not cause the Q-jet's particulate contamination. I'm not sure how long it takes for ethanol gasoline to evaporate from inside a carburetor, or if oxygen could eat up or weaken the carb's diecast metal threads over 5-10 years idle-time. The crudosis was created by some means. How many 40-year-old Q-jets does a professional rebuilder see where one owner has had it for 35, of which it just sat for a decade? Not too many.

Jennings did mention that ethanol/alcohol will cause an AFB carb's leather accelerator pump to peel up over time. This was also related to me by noted Carter AFB restorer/rebuilder Dick Katter in Manassas, Virginia (703/754-7547), and renowned Quadrajet restorer/rebuilder / NCRS seminar expert Jerry Luck in St. Louis. All three also noted that a helicoil could be installed on the worn inlet threads, and that actually is a common process.

After noting that the float's brass seat felt frozen in place, thus very difficult to unscrew, Jennings decided to leave it alone. He then re-epoxied the two secondary metering rod well plugs that Hedworth had first coated 30 years ago. Age and use via 66,000 miles of engine heat had cracked apart the epoxy on both. We've been told that Q-jets made in the first decade of their production (1965-'74 more or less) have plugs that historically tend to leak fuel out of the float bowl into the intake manfold plenum. This causes a richer idle-mixture, as well as an up-and-down idle-speed characteristic, which can be mentally baffling for laymen like us.




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