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Old 03-06-2008, 12:01 AM
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AirTech
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Default RE: Quadra 52 won't run under 3500 HELP

ORIGINAL: tkg

Back to basics..... Remove the carb, check that the buttery is installed correctly. The butterfly is NOT round but oval and has beveled edges for correct sealing at low speed operation. Unscrew the idle speed screw untill the throttle arm does not touch. Hold carb up to sun and see if any light leaks past the butteryfly, light leaks = air leaks = fast idle.
Hey Jim,

I don't want to sound obnoxious but tkg suggestion (see above) is a very good idea. I had the exact similar problem with a ZDZ 40 with a Bing carburetor and after messing with all the internal adjustments and trying to "re-design" the carburetor it came down to a simple reversed butterfly.

Most folks (I included) remove the idle stop adjustment screw. What happens (in some carburetors) is that the butterfly doesn't have a detent to stop rotating and the throtle lever may flip 180 degrees. In that case the carb will work just fine when you go full throttle but will not idle and die when the butterfly is closed. The reason being as tkg well explains is because the butterfly is not round but oval and beveled around the edges so it seals properly. Make sure to reverse the servo direction because when you flip the butterfly the full open and full closed directions get reversed too.

Trust me I seen this happen on several other engines. I friend picked up an almost new ZDZ (this time a Walbro carb) from this guy on the classified adds and when we tried to fire it up the same thing happened. The seller "swore" that the engine was running fine when he had it, and that he never touched the carb. After all he sold a dud and he wasn't ready to admit it. Take a break and start all over from the basics. You may find out your problem is much simpler than you think.