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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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.

Sources

Bob Jennings Dyno Shop
North Hills, CA 91343
818-894-3811
http://www.streetperformance.com
Eaglehead Restorations
Manassas, VA 20109
703-754-7547
Val Hedworth Racing
Macon, MO
660/385-2536
Jerry Luck Motorsports
Hazelwood, MO
314/895-1551

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