Problems after rebuild - need a little help

[71_k10]

Cliff,
I have rebuilt a friends quadrajet, (7042206) that is original to his 72 Chevy truck with an original 402 using your kit.  The carb was disassembled cleaned and carefully reassembled using tips from your book.  I have done several and have always had excellent results but this time I have a  problem. I offered to run this carb on my 71 with a mild 350 to make sure everything was good before I sent it back to him.  The engine will start great and idle nicely, hot or cold, but when I accelerate it will hesitate and stumble terribly until I hit probably 3/4 throttle.  from that point to wide open it runs great and my 350 makes good power.  I had the float at .250 initially and have since set it at .375 and no change.  I verified the accelerator pump is working and I can kill the the engine if I close the idle screws.  Its just completely hosed off idle, at 30 mph the engine stumbles bad and sounds like its missing, which doesn't happen with my quad on it.
My question is, would this be normal for this carb, (from a 402) to run like this on my 350 or do I have a some other problem? I guessed on the power piston spring, perhaps to stiff? 

Thank you


Jeff

[Cliff Ruggles]

A 7042206 is a large main airbleed unit, and they are very lean on the primary side of the carburetor, both at part and heavy throttle.

I would move the float level back to 1/4".

Does this problem occur at light throttle, heavy throttle, full throttle or all three?.....Cliff

[71_k10]

I would say light throttle only,  heavy and full throttle sounds, feels and pulls great.  Again starts are great, idle is good. 

Thanks
Jeff

[71_k10]

Sitting here thinking about it , I'm going to change my story and say the problem also occurs at heavy throttle also. 

Jeff

[Cliff Ruggles]

Did you free up the APT screw in the baseplate?

We install an external screw on those models so we can raise/lower the power piston to fine tune the part throttle A/F ratio once the carburetor is placed in service.

We also install smaller main airbleeds, and our custom jets/metering rods.  This will increase fuel delivery to the engine across the entire speed/load range. 

I've tried larger jets in those units with little or no improvement.  If it makes you feel better, we get more complaints from folks who are rebuilding the large main airbleed Chevy carbs than any other.  They used that set-up from 1970 till 1978 on most models......Cliff