Having trouble with idle on my OS FX.Starts fine full throttle ok,but when
I idle down it takes 30-45 seconds before the rpm's even change then
the idle gets progressively slower and stalls! Can I adjust the low mixture
srew while the engine is at idle ? The manual states the barrel must be closed.

Shouldn't need to be at full throttle to start it. Matter of fact, that's rather dangerous.

Do you have the instructions? If not get them from OS's website. If this is a new engine, follow the directions exactally, break the engine in IAW the manual. Sounds like you have an air leak somewhere, should shut down immedieatly with throttle barrel closed, or is it not closing all the way?

In any case, I hate to sound insulting, but get and read instructions..... and post more info (how long has engine run, needle settings, etc etc, what's it on, as much as you can think of)

Andy

UHHHHHH If the barrel is totally closed, then its supposed to quit. You might want to take it to a local field where someone can show you and help you with the adjustments in person.

If the barrel in the carb is fully closed, it should shut down immediately. Taking that long is an indication of an air leak somewhere. I would check that the carb is fully seated on the o-ring and also check the backplate.

assuming you have no air leaks the way to do it is this-get a dressmaking pin and close the throttle barrell down until it is pinching the pin,then wind the slow running adjuster in until it seats,attach a clean piece of fuel pipe to engine fuel inlet. blow down the pipe,keep the pressure up and slowly undo the adjuster until you feel pressure releasing in the pipe-you may hear it first,when this is done it will be spot on.p.s. don't forget to take the pin out!!