The Stovebolt Site Forums The Shop Area Engine Shop Carter YF hesitation on a 57 3100

I have a NOS Carter Zip-Fit Carburetor YF 3211. It was complete with the heat stove and all the fittings. The carburetor runs great with the exception of initial hesitation upon acceleration. I have to feather the throttle, and then the engine takes off and accelerates strongly. The engine cruises down the road very well.
I have replaced the diaphragm in the accelerator pump. I can see gas squirt in the throat of the carburetor while pumping the throttle. It acts as if still not pumping enough gas. Are there any check valves or passages the carburetor that can cause these symptoms? I have leak checked the exterior of carburetor with starting fluid and found no vacuum leaks.
The engine is well tuned; it ran ok with a leaky Rochester carburetor.
Any ideas would be appreciated.

If the hesitation is from an idle, the idle mixture control screw may be out too far.

If you live in an area where deathanol is served at the fuel pump and the hesitation is from an idle, you may need to open up the idle tube in the carburetor.

Also, while you commented that your engine is well-tuned, do not discount the possibility of ignition timing on a hesitation.

And one other possible issue. Since you mentioned that the carb is N.O.S.; Carter used velumoid gaskets (as did Rochester and other carburetor manufacturers during this time period). These gaskets shrink over time. When installing a N.O.S. (new old stock) carburetor manufactured before 1990, ALWAYS disassemble the carb, blow out all passageways (spiders, dirt-daubers, etc.) and replace the gaskets. Then you truly have a new carburetor.

Since you mentioned that you replaced the diaphragm, hopefully you blew out the passages and replaced the gaskets at this time.

Jon.

Thanks for the suggestions. I will play with idle mixture screw to see what happens.

The carb has new gaskets with the exception of the throttle body to the fuel bowl. The one in my kit was distorted. I should probably get a new kit to play it safe, I am doubtful of kit’s quality and age. I did not soak the carb, I just disassembled and blew out the passages.

There is booze in the gas in my area. I am not certain what percentage. I believe it varies with summer and winter.

You probably did all that was necessary. Soaking should not have been required, if you blew compressed air in both directions in all passages.

Try the idle mixture screw first. If that doesn't fix the problem, it may be necessary to borrow an exhaust gas analyser to determine if your mixture is too lean or too rich at idle (either will cause the hesitation).

Jon.