Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

WOT Stumble with Pinging

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429bbf:
lets think about whats going on. you say if you only go 2/3 throttle it works fine . what happens at 2/3 throttle thats right when the rod starts opening the bottom barrels. it seems to me your going lean, ether not enough fuel coming from the poe or maybe we need to lift the needles on the secondary a little higher or faster. i would have to have this in front of me to figure out .it sounds like its not getting enough fuel before the top flaps start to open and raise the needle . it acts like a vacuum leak between the base plate and the fuel bowl in the back. not allowing the fuel to be pulled in the right amount. i had a carb that had an extra hole in the fuel bowl going to the base plate . exiting in the rear venturies . massive vacuum  leak when the secondaries were engaged.acted a lot like your talking about .that old of carb shouldn't have that.i tapped and plugged it and fixed the problem. hth

von:
Another possibility is a worn plastic cam that lifts the secondary rod hanger when the secondary air valve (flaps) open. If the hanger doesn't raise enough the rods don't get lifted to the smallest (richer) diameter in the jet opening.

KJMason:

--- Quote from: 429bbf on May 11, 2015, 09:00:04 PM ---lets think about whats going on. you say if you only go 2/3 throttle it works fine . what happens at 2/3 throttle thats right when the rod starts opening the bottom barrels. it seems to me your going lean, ether not enough fuel coming from the poe or maybe we need to lift the needles on the secondary a little higher or faster. i would have to have this in front of me to figure out .it sounds like its not getting enough fuel before the top flaps start to open and raise the needle . it acts like a vacuum leak between the base plate and the fuel bowl in the back. not allowing the fuel to be pulled in the right amount. i had a carb that had an extra hole in the fuel bowl going to the base plate . exiting in the rear venturies . massive vacuum  leak when the secondaries were engaged.acted a lot like your talking about .that old of carb shouldn't have that.i tapped and plugged it and fixed the problem. hth

--- End quote ---

I completely rebuilt this with one of Cliff's kits so I'm pretty sure there aren't any extra holes that fit your description.  I tapped and plugged the typical fuel leak sources in the primary and secondary fuel wells.  Now that I think about it, I wonder if I might have set the plugs too deep in the secondary wells.  When I was rebuilding mine I read where someone had inadvertently blocked the wells so I made sure they were clear (even ground the set screws that form the plugs down to make sure they didn't go too deep)  but I suppose I could have gone a little too deep causing a restriction.

Von, I installed a brand new cam during the rebuild but is it possible to install the cam the wrong way?  IIRC, the large lobe on the cam points toward the front of the carb and the rods seem to lift correctly when the air door is opened but maybe I got the cam backward?

I guess I should just pull the carb again and disassemble/reassemble it to make sure I didn't do something stupid.

429bbf:
just a thought . are your secondary tubes pushed to far into the housing? im sure you checked this on rebuild but sometimes i guy gets in a hurry and misses a few small details .fwiw

KJMason:

--- Quote from: 429bbf on May 14, 2015, 05:30:00 PM ---just a thought . are your secondary tubes pushed to far into the housing? im sure you checked this on rebuild but sometimes i guy gets in a hurry and misses a few small details .fwiw

--- End quote ---
Actually, the tubes were originally pushed in all the way to the pickup tubes so I pulled and trimmed them at an angle per Cliff's book so there's no obstruction there.  I opened the holes into the secondary wells a tiny bit and plugged the very small holes adjacent to the POE tubes in the air horn.  Again, these mods were all detailed in Cliff's book so I don't think they'd cause the problem.  Still stumped here.

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