Several weeks ago my engine in my 641 made a terrible racket. I shut it down. Did a compression test (compression was very low) Did a complete rebuild of the head and bored the cylinders. Thankfully crank just needed a polish. Never found the source of the noise. Machine shop guy thought carbon on top of one of the pistons. He even pointed out where something had hit a piston. Last night I removed the carb for cleaning because I could not get it to run just right. Put on a replacement carb I had sitting on a shelf and it runs much smoother now. Took a look at the carb and noticed one of the screws holding the butterfly valve is missing! I know it was on before. I'm betting it got sucked into the engine and then was expelled when I did the compression test.
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