Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Edel 1901, AMS out, Still Lean at Idle
bry593:
I'm having an issue with a rebuilt Edelbrock 1901 quadrajet. First off, here is my engine:
413 CI sbc, Crane .427/.427 lift cam w/110 center, Dart Iron heads w/2.02 valves, appx 8.8 to 9:1, iron quad, 2" rams into dual 2.25" pipes, GM HEI w/14 initial, 36 @ 2500 rpm and 50 at cruise.
I bought the rebuilt 1901 carb to replace a warped 4MV that was unresponsive to mixture screws. After bolting it on, I proceeded to adjust the mix screws. At 4.25 turns out, I achieved 18.5" Hg, but then could not reduce idle speed to 750 rpm. A quick check showed that the fast idle was off and the primary throttle plates completely closed.
My first instinct was to check float level and it was found to be .420" (and the needle was clipped at the wrong side of the float bar). Being that this is a 4MV carb, I set the float to somewhere between 5/16 and 3/8. This didn't help. Upon reassembly, and readjustment of AMS (again 4.25 turns), I placed my hand over the choke horn and the idle momentarily increased. Still lean... I then proceeded to check for vacuum leaks with a propane torch, but none were found. Maybe I should use something with a bit more zip, like starting fluid?
My next attempt was to richen the main jets from the original 69 to 71. This along with the original 36B needles. Upon reassembly and placing a hand over the horn, the idle momentarily increased. Still lean?
To maintain my initial timing and target idle rpm, I have connected the distributor advance to ported vacuum.
My questions are:
* What is your recommendation for richening the idle?
* What can I do to reduce the idle to allow for 750 rpm with manifold vacuum on the advance?
* Is it possible the carburetor has a small internal vacuum leak?
Thank you for your consideration,
-Brian
429bbf:
welcome to CHP you need to measure the idle tubes and down channel channel restrictorsand the idle air bleeds. .they play a very important part of what you are doing. i would start with receipe 2 for my idle . if you throw some sizes of that stuff out here someone will gladly help you.jets and needle do very litttle to fix your problem . hth.
bry593:
Thanks, I had heard the idle circuit is rich on the 1901 and was hoping it would be less involved. But, this will be good experience. Just a little worried I'll ruin a good carb in the process.
I currently don't have gauges small enough to measure the diameters. I'll check with air/gas and see if a tip cleaner looks suitable.
429bbf:
remember the idle tube restrictions are down about 2 plus inches. your standard drill bit will not reach. fwiw
bry593:
I ordered the 61-80 bit set and pin vise along with cliff's book. Hopefully these will be long enough. Will get everything measured as soon as the items arrive.
I read somewhere that the 1901 is actually supposed to have a .420 float level. Is this correct?
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