illustrated diagram of carburetor on 25cc McCullough lawn brush cutter.?

Answer 1

I want to caution you on this point. Do not assume because the engine does not run or start properly that it is in the carberator.

The 25 ccMc engine has internal reed valves, all 2 cycle engines have those. What happens is those reed valves allow the passage of gases back thru the carb instead of creating a constant intake suckage.

First try cleaning those reed valves before tearing into a simple carb such as that which probably doesnt have a thing wrong with it. Get some regular Auto carb cleaner and spray it right down into the engine as the engine is runing half speed.

If that carb cleaner doesnt do the job dismantle the engine and you will most probably find a small crack in one of the reed valves at the bend line. Replace those and your engine in 99.99999% of cases will be just fine.