Quadra-jet problem

[Kurt G.]

I'm the lucky owner of one of the fabled Monday morning cars that has a quadra-jet of the pick-up assembly line. I doubt that has anything to do with it, but I'm having one "H" of a time keeping it running right. One time I drive it it runs lean, the next time rich. Sometimes I pull up to a stop light and it idles great, the next time, like it has a 3/4 cam in it. I'm to the point of scratching all the hair off my head. The linkage is a tiny, and I mean tiny bit loose but I wouldn't think enough to cause the problems I'm having. Does anyone have a recommendation on where to send this thing to get it overhauled with new seats, bushings, float, etc. that won't cost an arm and a leg but will do it right the first time? Thanks in advance.

[Patrick H.]

Re: Quadra-jet problem

I'd try this place:

http://www.cliffshighperformance.com/

Cliff Ruggles wrote the latest book on Quadrajets, and I very much have enjoyed reading it.

Patrick

[Harmon C.]

Re: Quadra-jet problem

You may just spend money and still have the same problem as I did. Take out the brass seats in the bottom of the bowl and see if you get a bunch of dirt out when you run the starter and pump some gas through with them out and a towel over the carburator. That is what fixed mine $750. later over two years and two rebuilders two chances for both of them. I just kept putting the Auto Zone carb back on and sending out the numbers matching and more money. The junk must have been in the base as the filter was clean. I fixed it in a parking lot along the interstate going to a meet.

[Randall K.]

Re: Quadra-jet problem

...one of the fabled Monday morning cars that has a quadra-jet of the pick-up assembly line.

This caught my eye. When I bought my '72 454 back in 2001, I ran the numbers on the carb, which as I recall turned out to actually be a truck carb. My assumption was that it was replaced years ago in service or by bubba. I found a carb for a '73 454 that's at least in the right ballpark for the numbers.

Unfortunately, I'm at work, so I don't have the old truck carb numbers with me. What was stamped on yours?

I've also never seen a reference before to incorrect carbs. Is there any more info out there on this?

Thanks
Randy

[Kurt G.]

Re: Quadra-jet problem

Randall, unfortunately I'm not at home, and won't be until after the 21st of the month, but, I got my information on what my carb was from a friend in the Oklahoma chapter of NCRS. The rumors about the truck carbs on vettes is not really a rumor, I think it is just that GM never wanted to own up to it. The part that really sucks is that any documentation that the truck carb on my and your car are the ones that they left St. Louis with was destroyed many years ago, so, as they say in the judging manual, the proof is on the owner. PM me and when I get back in town I'll send you the name of the book my friend sent me a copy of, or Mike, if you see this thread, send a reply so Randall can see it.

[Michael W.]

Re: Quadra-jet problem

This is the first I've heard of 'truck carbs' being factory installed on Corvettes. Over the years I've seen carbs installed on Corvettes that started their lives on just about every other GM vehicle that ever had a V8 with a four barrel. Much like starters and alternators, once they go through a rebuilder's shop the numbers become pretty much academic.

My 'spare' carb is presently configured for my '73 small block and looks every bit the part, but the numbers say it started life on a late 70s Olds.

[Michael A.]

Re: Quadra-jet problem

Randell send an email to ikelee@olp.net and I will send you the files I sent to Kurt about 1972 truck Q-Jets.

[Jack H.]

Re: Quadra-jet problem

A Jeckyl & Hyde curb idle situation (when engine is hot and you decel to a stop, you get a different idle RPM, higher than what you set at tune up time), can be the result of distributor + emissions control system problems...

Specifically, the centrifical weights can be 'sticking' inside the distributor to the point that sometimes the return springs pull them fully back and other times they don't. That's easy to check with the distributor cap and rotor off...

The emissions angle is these cars have TWO idle settings. One is what you set at tune-up time (dist vac disconnected) and the other is dictated by the emissions system (on a '70 that's the TCS, transmission controlled spark system). The TCS solenoid controlling vac to the distributor engages when the tranny is in high gear mode (highway cruising) and releases when the tranny is in low gear/no gear.

The system EXPECTS the TCS solenoid to be clean and crisply functional, but if it's 'clogged' with grease/oil, it can 'stick' and fail to fully release after a highway cruise where it's been engaged/operative.

A test to see if the Jeckyl/Hyde idle is related to non-carb issues, is simple. Go for a drive and recreate the abnormally high idle condition. Then, put your foot on the brake, shift into gear and START to let the clutch out.

The engine should 'bog' as it tries to move an excessive load causing RPM to fall. Do NOT let the engine stall! But, simply FORCE it down below the artificially high idle RPM plateau.

Then, shift out of gear and release the clutch. Did the engine return to its lower RPM profile as you'd set it at tune-up time? If so, that's STRONGLY suggesting the problem lies with either your distributor's centrifical advance not returning properly OR your distributor's vac advance failing to release.

On emissions controlled cars, the vac advance is pretty much a 'prisoner' of the emissions system...