Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Diagnose a Quadrajet carburetor problem => Topic started by: Tjesse on January 01, 2017, 02:25:51 PM
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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.
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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
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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.
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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
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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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Hi Cliff,
I couldn't resist any longer and opened it up today. I found many things wrong...
- That little clip between the float and the needle; simply NOT there :o
- Float level (without that clip) is 11/32 in stead of 7/32"
- Primary metering rods are 43B in stead of 44B
- Primary metering rods hanger; bent (upwards towards a rich mixture)
The 'rest' looked clean and nice and according to the factory specs.
I will order the required parts from you this week.
Thank you for your support!
Grtz, Tjesse
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You don't need the clip, if the hanger was bent that might be part of the problem. What size are the jets?
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Hi Jim,
The Jets are 74.
Thanks, Tjesse.
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Forgot to mention that also one of the 74 Jets was partially blocked and I suspect preventing the rod to lower into the Jet for a lean(er) mixture. With as result both supplying a too rich mixture.
Grtz Tjesse
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if you don't do anything else replace the acc. pump with a good quality like cliff sells or else you will be back in that carb in a very short time. fwiw
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Check to see if idle bypass holes are blocked in main body.
Also check pin in bottom of power piston to see if it has been cut off.
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Hi guys,
Many thanks for the replies and advise provided. I will continue with the inspections this or next week.
Will update when I have more details ;D
Parts are ordered from Cliff!
Grtz, Tjesse
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;D Parts received from the US so the rebuild can begin 8)
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It is done 8) Carb reassembled, adjusted and installed on the Corvette SBC.
Didn't have time to start it up today so that's scheduled for next weekend, fingers crossed.
Looking forward to the result & the fine tuning, can't wait to hear that engine run again!
Youtube links will follow ::)
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8) Today was a good day !
Refueled the Corvette and fired it up after the rebuild: https://youtu.be/R4eDzl5VClU
Ran very very nice and only needed little adjustments to the idle mixture screws to obtain the good vacuum and a smooth idle, despite the nice cam!. The difference with the video before the rebuild is huge. The Engine isn't running rich at idle and at part throttle anymore, no black smoke, no bubbly sound from the exhaust, washing the cylinders with excessive fuel, just perfect. Of course, I may need to fine tune by changing the power piston spring and altering the APT, etc but for now I am very happy with the results.
Thanks Cliff (and others here) for the great support to a gearhead in the Netherlands ;D
Here are two other vids after the adjustments:
https://youtu.be/mEIE94OozWE
https://youtu.be/x286AXmUtfQ
Again, thanks all!!! Grtz, Tjesse
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Good news!