Got 35 briggs with mikuni,Also has all internals done too. Has bog from about 2500 to 4000 rpms. After 4000 rpms seems to run somewhat ok. What could cause this?

Was this one running good one day then went south or is it an issue since it was built? Could be a tuning issue , fueling issue, gasket failure, valves, etc

Just started getting worst. Had cracked block, so while I tore it down, had valve job done on it to try fix problem. But didn't help. Also cleaned carb but didn't notice anything there either.

Sounds like a tuning issue or possible cam timing issue. A wideband o2 sensor with a bung welded in the pipe will be a good place to start. Degreeing the cam would find a cam problem if it has one. Any chance your needle is set too high and fat?

Haven't changed anything on carb since first put together, just recently started acting up. Heard to put clip down a notch and try that on needle?

If you are lean in the mid then yes moving clip down 1 will fatten it up

I agree with wills first suggestion. I'd drop the needle (move the clip higher 1 notch). If it was backfiring mid throttle, I'd say raise the needle. It's bogging, though, which sounds like too much fuel.

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