Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Freshly rebuild carb: low vacuum, very rich off-idle to part throttle. PLS HELP!

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Tjesse:
Hi guys,

First of all, happy new year! May 2017 bring lots of fun, cruising, etc ;-)
I am posting this message to request some advice from the people with the knowledge of the Quadrajets
as I am facing a problem. I bought a 'nicely' rebuild carb 7 years ago and installed it 6 month ago.
It has PN 7043213 for my 1973 L82 SBC350 Corvette with a 4 spd manual. It bought it on eBay for quite
some $$$ from:

Carb Master
PO Box 612404
San Jose, CA 95161
USA

With that carb, the idle mixture screws don't do anything when using the vacuum gauge. It also shows a
very low, but steady vacuum, approx 7-8 in Hg and it runs rich.
When fixed at 2500 rpm, the engine also runs rich, grey/ black smoke from exhausts, hot(ter) headers,
black plugs and it sounds bubbly, all symptoms (to me) for running rich.

At first, I checked the complete engine, measured compression, re-did the ignition, checked for vacuum leaks,
etc but all good and the problem remained. As the carb was fully rebuild I didn't suspect it. For isolation purposes,
I installed a correctly dialed in Edelbrock from an identical engine. The engine ran flawless, spot-on with correct
vacuum readings of 17 in Hg and a normal mixture. So I know it is caused by the Quadrajet carb. Something is wrong...

The rebuilder is not responding to any emails and I am about to open it up for investigation. I suspect there is something wrong with the primary section which results in the rich mixture. I can't tell yet what might cause the poor
idle with the low vacuum.

Who can provide me with some tips or specifics to look for? I have bought & read the bible by Cliff Ruggles "How to Build
and Modify Rochester Quadrajet Carburetors" and below are my suspected items:
- float type and level
- primary jets/ rods (type/ size)
- power piston spring (incorrect force installed?)
- binding of any mechanism
- etc?

All info is highly appreciated. I have a video on youtube of the Engine running with that Quadrajet where it shows the
smoking exhausts and the bubbly sound. Again, with the Edelbrock it was all good so we can rule out the Ignition
settings, fuel Pump (5.5 psi), Engine condition, etc.

www.youtube.com/watch?v=FN07YAzl1Vs

If I lived in the US I would have send the carb to Cliff for inves and corrections however as I am from the Netherlands,
this is not so easy. I am an aircraft power plant Engineer, I rebuild GM engines and transmissions but diagnosing this
carb issue is a first for which I kindly request help from the pro's! ;-)

Many thanks in advance, Tjesse.

Cliff Ruggles:
I would NOT continue to try to use the carburetor as obviously it is not working correctly and "washing" the engine with fuel.

Take it completely apart and see what is going on.  Might be something as simply as some trash in the needle/seat assembly, incorrect float adjustment, or even the little clip on the needle hooked into one of the holes on the float arm causing it to stick and flood.....Cliff

Tjesse:
Hi Cliff,

Thank you for your reply.
I ran the Engine three times with the Quadrajet before I swapped it for the Edelbrock.
Unfortunately the Quadrajet was installed while breaking in the Engine after rebuild so I hope it didn't cause
any damage. Looking back at it, it was definitely washing the Engine. Just to be sure I'll remove the heads to
inspect the cylinder walls etc as it did run quite hot due to the washing once. Now, with the Edelbrock, it runs
perfect so hopefully no damage done by the washing. I will open up the Quadrajet this week for inves.
Quite disappointed after paying a lot of $ for the carb and it's no good. It was the only item of the Corvette which
I didn't rebuild myself  :-\ Lessons learned.

Many thanks and with kind regards,

Tjesse Rodenburg
The Netherlands.

Cliff Ruggles:
The good news is that if the correct factory q-jet were rebuilt and set-up correctly, it would work better everywhere than the Edelbrock carb.

Obviously you got hooked up with a "builder" who doesn't have a clue as to how to set up that carb, probably didn't use good parts either.  It may have even been thru one of the commercial "remanufacturing" processes judging by how poorly it works......Cliff

Tjesse:
Hi Cliff,

I'm afraid you're right. Also because the 'rebuilder' is not responding at all to any of my emails whilst still being
active on e.g. eBay. Anyway, I'll take it apart and will post my findings for the completeness of my post here.

Again, many thanks Cliff.

Kind regards, Tjesse Rodenburg.

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