Q: I purchased and installed the rebuild kit I received from you for my YF2100S carburetor. It is mounted on a 1946 Chevy truck with an in-line 6. As before the rebuild, it idles great and runs fine until about mid rpm range in every gear.  Beyond that however the engine starts to spit and sputter.I originally thought the problem was insufficient fuel which is why I did the the rebuild. Post rebuild, and with no noticeable change in symptoms, I pulled a plug (all new) and found them to be black with soot buildup. So now I’m thinking to much fuel when the throttle is beyond mid-point.I have disassembled the top of the carb and all appears to be in order. The metering rod seems to be in place. There is no evidence of gas leaking on the outside of the carb. And, as mentioned above it idles fine and runs good to mid range.A compression test has all 6 cylinders within 10% of each other averaging 115 psi.

The black plugs suggest flooding, or too rich.

A: The fact that it was going on before the rebuild tells me to 1st look at the ignition. Bad plugs can cause high end loss of power for sure. Same with wires.

Once you know the ignition is OK then start looking into the carburetor.

By chance if this carburetor was transplanted before this all started then the problem may be the carburetor main jet is too big.

Did you test the float when rebuilding? Heat up water just prior to boiling and immerse the float. Any bubbles means it's leaking.

Gently move the float up and down to see if you can feel any catching. The float pin could be worn. Also the float should be aligned in the middle.

Make sure the  choke valve is wide open when the engine is warmed up.

Check for proper adjustment of the metering rod. If it isn't coming up far enough it would restrict the fuel.

Look in our YF carburetor manual and go over the metering rod adjustment.

Follow the main jet passageway to make sure it is clear. I've seen crud build up below the jet causing a restriction.

Test the fuel pump to make sure it isn't too low. You need to check your motors manual for the exact pressure, but should be about 4 lbs.

FOLLOW UP:

I followed your advice and worked the ignition system. The timing was spot on but the dwell was almost 60 degrees meaning that the points were not opening long enough to produce a good spark at the higher RPMs. Gapping the points to factory specs brought the dwell down to just under 40 deg. Further adjustment is required but the problem is essentially solved.