A lot of time you will find that even a new carburetor requires adjustment right out of the box. If you find that your engine is stumbling off idle and has a hesitation it is because of a carb tuning issue. On Holley Carburetors make sure that you check the accelerator pump adjustment. You will need to check and adjust accordingly to get rid of a bad stumble or hesitation.
The main parts of an accelerator pump consist of the pump diaphragm, pump cam and pump nozzle. You want to first check and make sure that the fast idle cam lever is disengaged; allowing the operating lever to open all the way. From there you can check the clearance between the accelerator pump diaphragm arm and the operating lever screw and spring assembly. The rule of thumb is that the arm should be barely touching the bottom of the operating lever screw; but have no major slack in it’s range of motion. If there is a lot of slack you can simply tighten it all up. A .015 feeler gauge can be slipped in between the lever and the stop to check for clearance.
Once all of this has been checked if you’re still having hesitation issues you may need to move up nozzle sizes. We suggest checking with Holley or your Carb Manufacturer for their list of nozzle sizes. Too large of a nozzle can cause bogging and flooding of an engine if you go too large.
Hopefully these quick tips give you some help with carburetor bogging issues. To see our entire line of Holley Carburetors visit our site HERE.