Thanks for the replies. The engine is a completely stock YS 10:1 69 400. My total timing is about 36 degrees. It did have a lot worse of a stumble so I replaced the umbrella on the accelerator pump today. The old pump umbrella was maybe 5 years old. I have never run ethanol fuel through it. The old umbrella didn’t look horrible. The stumble is nowhere near as bad but it is still present just off idle when I take off. The inside of the carb did look very clean. I blew all of the passages out with carb cleaner and compressed air. One thing I did not mess with was the little screw under the metal plate on the airhorn. I’ve worked with the air mixture screws but that did not help. The accelerator pump rod is in the inner slot on the arm. It did appear to be wore some. It idles great and runs great cruising. The flat spot taking off is just annoying.
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