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Old 07-04-2021, 10:36 AM
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Default Which OS 40 engine model is it?

I would agree with post #2 and #5 as my first step to get this adjusted. I would richen the idle air bleed screw 1/8 of a turn at a time between test runs to see what you get IF THIS IS A FP or LA air bleed carb. See photo.
If the OS 40 is a FSR, SF, or FX, then it's not an air bleed carb and your low speed is made richer by turning the screw counter clockwise to richen it. If it flames out after making these adjustments, then you likely have a blockage in the line, but I wouldn't expect it to even run if that was the case. It wouldn't hurt to remove the needle to clear it out, some tank debris could be blocking it.
How many seasons are on this engine? What model engine is it? Filter all fuel going into the tank. Don't use a filter on board, they usually are too restrictive.

Finally, you could also remove the bolts to the head on these engines and inspect the liner. The nickel liner can peel and give you running problems as well. ​​​​​​ OS is not dead proof. All depends on what abuse it's endured in it's history. I often buy second hand engines and always deal with problems they gave up on troubleshooting.

Last edited by J330; 07-04-2021 at 10:48 AM.