on disassembling the carb, the only thing I could suspect was the oring on the main jet, where it sticks into the float bowl, is a little flat. Came to me in my sleep that it could be a cause.

What it is doing is: When first take off it runs great up to 7000 rpm, smooth acceleration. By the time I get to top half in third, it goes to sputtering and cutting out. By forth and fifth I can get it to 4000 rpm, but still sputtering. I can back off the throttle at about 40 mph and maintain that speed. If I try giving it more throttle, it starts sputtering again. Two weeks ago it was running normally.

I may have solved my problems: First, I elimated the inline filter since there is a scree inside the petcock (late style). This did not give any inprovement. So, I took another drive and got to opening the air screw. This did improve with each 1/4 turn outward. After the 3rd time, I think I have it, I may go 1/4 more, but ran out of time this morning.

The air screw will only affect running at very low engine speeds. If you are 100% certain the carb is working properly, it would be a good idea to check the points and see if there is any evidence of condensor failure.

Finally got time to go over it all again. I washed and re-oiled air filter. I did not go into electrics, as it stated fine and ran well, until 3 k rpm. On third carb cleaning, I got a white pan and white towel. Doing surgery style. Carb cleaner thru every port and passage in the carb. Laid each piece out on the white towel an reinspected to make sure all were open. There were some small black bits in the white pan. AHA! Reassembled and it runs fine.