Q-Jet Carburetors - Super Chevy Magazine

Oh No, Not Again!
With all new gaskets, Jennings installed the Q-jet on his V-8 Chevy dyno engine to make final external air/fuel mixture and idle-speed adjustments. It ran perfectly. The next day it acted up again--just like before. I suspected there were more diecast particulates under the frozen-in-place brass seat. No fault of Jennings.

To remove it takes a very wide, long, flat blade screwdriver. Harbor Freight to the rescue! After very careful back-and-forth unscrewing (to save the diecast threads), we were aghast to find many more deposits. The threads on the brass seat were also completely packed with crudosis (see photo 8). We assume this was from many years of dryness. It became ultra hard--even sort of petrified. After cleaning and reassembly, the Q-jet ran perfectly. But what next?

Jennings had done a fine job, but were there multiple reasons for this dilemma? What would you do if this was the original carburetor from your 40-year-old Chevrolet? I decided that further use would eventually be a cause for heli-coils. Nothing wrong here, but I decided that until I can gather more facts, and the cost for professionally installed helicoils, I ought to remove the original Q-jet. I replaced it with a like-new Q-jet I bought years ago (thinking some day I might need it).

I also decided to visit eBay - where as luck would have it, I was top bidder on a used, 750 cfm AFB carburetor. From my 409 racing days in the mid-'60s, I have a ton of metering rods and jets to super-tune it for this 350. My Project Econo-Performer Monte Carlo has long since retired from drag strip parts testing and its 66,000-plus miles of continual mpg testing. So, it will now sport two efficient carbs, a nearly identical Q-jet, and a Carter AFB. We'll see if either gets eaten up. I don't plan to take either apart unless one burbles out for help.

In the world of longtime vehicle ownership, this Q-jet carb problem and other simple woes are nothing new--except you never hear about them.

We hope you have learned something new here. We sure did.

9 Here is the brass seat exactly as it was removed. Note the thread contamination.
9 Here is the brass seat exactly as it was removed. Note the thread contamination.
10 I used aerosol carb cleaner to blow out the diecast particulates that were under the needle and seat. I then followed up with compressed air to blow out everything. Question: Will the crud continue to evolve?
10 I used aerosol carb cleaner to blow out the diecast particulates that were under the n
11 Here are the previously epoxied secondary metering rod well plugs. The engine did have a slight rolling idle. Jennings re-epoxied both. Engine idle-speed now rests smooth and rpm is a steady 650.
11 Here are the previously epoxied secondary metering rod well plugs. The engine did have

12 Besides re-epoxying the secondary metering rod well plugs, Jennings also epoxied the outer fuel inlet plug--another early Q-jet weak link area.
12 Besides re-epoxying the secondary metering rod well plugs, Jennings also epoxied the o
13 It always pays to test your work prior to getting down the road. Bob Jennings Dyno Shop has a chassis dyno and a test-engine dyno. They can run your car on the dyno rollers for added power output tests and mods, as well as run your carb (like they did ours seen here) on their own Chevy dyno engine.
13 It always pays to test your work prior to getting down the road. Bob Jennings Dyno Sho
14 Ladies and gentlemen, meet the legendary Bob Jennings. A native Virginian (Norfolk), he came west to Southern California in the '50s and stayed.
14 Ladies and gentlemen, meet the legendary Bob Jennings. A native Virginian (Norfolk), h

SOURCES
Eaglehead Restorations 11135 Poplar Ford Trail Manassas VA 20109 703-754-7547 mailto:katterscarbs@aol.com	Jerry Luck Motorsports Hazelwood MO 3-14/-895-1551
Val Hedworth Racing Macon MO 6-60/-385-2536	Bob Jennings Dyno Shop 9519 Sepulveda Blvd North Hills CA 91343 818-894-3811 www.streetperformance.com