Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Diagnose a Quadrajet carburetor problem => Topic started by: zacman on October 10, 2014, 03:55:27 PM
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Hello
I recently rebuilt my carburetor, 1984 quadrajet 4 barrel on chevy 350 in my rv and now I cant pass emission on the high speed test. Co level at 10 were at 1 before rebuild. runs rich. used parts from quadrajetparts.com. I have tried several float levels and tried putting old float and old seat and needle in but no luck. no matter what I seem to do it always fails the run test. It passes all the idle test and run hc test but all my readings are much higher then it was. I have not removed the idle screw plugs or messed with the idle screws or removed idle tubes. after 7 fails I disconnected pcv tube, and distributor tube so it could get more air and cranked the idle and I passed. but 5mpg sucks. also first time I parked it smelled of gas bad. lower float seemed to help that. tried lots of different timing settings as well. please help.
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with that kind of mileage you may as well bolt on a holley (no pun intended) did you put in throttle shaft bushings?lots of time when you clean up the carb they suck a lot of air through the shafts .first thing to do is get good quality parts and totally strip the carb. then when you get done it will run like a champ.back in the 70's i used to rebuild a carb like that (1/2 rebuild )they ran ok but never quite right. now i dont mess around i strip them down to bare and put in the best parts i can buy .end results are awsome.fwiw
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I would install our needle/seat assembly and accl pump.
Make sure the power piston hanger arms are level and EXACTLY even. Our kit comes with a new retainer for the PP to keep it in place during assembly.
Most likely the hanger arms got bent during the rebuild and throwing the high speed running test out of calibration.
The biggest reason to use our kit is that it will have the correct size fuel inlet seat, which effects fuel level at any given float setting. For stock set-ups I would use the stock factory recommended float height, unless the fuel pump has been changed and fuel pressure is not the same as the OEM pump.
The idle tubes at a minimum should be cleaned, we remove them here, but they can be cleaned out without taking them out of the casting. It's just difficult to clean under them so it's always best to remove them and size them with a precision drill bit in a pin vise.
I would also install a removable set screw in the airhorn so you can access the APT system and lean out the carb for emission testing, and fine tune the part throttle A/F afterwards without taking the carb apart.......Cliff
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I cant pass emission on the high speed test. Co level at 10 were at 1 before rebuild. runs rich... ...It passes all the idle test and run hc test but all my readings are much higher then it was... ...5mpg sucks... ...first time I parked it smelled of gas bad.
High CO = overly-rich mixture. Confirmed by horrible fuel economy, etc.
Got a plugged air bleed(s) for the main circuit? Power piston seized "up"?
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Well Cliff was right on with the bent hanger arms, they were all out of wack. Got them perfect again and Co levels went from 10 to .5. But now I am having vapor lock, could it be carb related as well? Too lean, float level, fuel pump? Engine running cooler than ever with all new cooling system. Just wondering before I dive into it again.
Thanks again!
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Did you install one of our N/S assemblies? The motorhome carbs require the high float N/S assembly, and I'd upgrade the accl pump while you are in there. Set the float at the correct level, and should be good to go.....Cliff
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I did install new needle and seat, it was a little different with a window in it. I changed the spring and rubber gasket on accl pump. Changed the float as well, but when I set it to the specs on the sheet the carb was smelling of gas bad so I lowered it. When I measured the factory one it was at 22/32. not sure what I set it at now. What level should it be set at? and would that cause the vapor lock/running out of fuel?
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So you didn't use the correct N/S assembly or put a good pump in it. To get the fuel level correct, you must use the correct high flow N/S assembly, new float, and I'd put one of our complete accl pump assemblies in it while you are in there.
Set the float to the correct factory setting if everything is stock on the engine and it still has a stock fuel pump on it.....Cliff