I've got an old OS60 FP. I got some guys from my local club to tune it for me and i'm pretty sure my low end mix is in an acceptable place, at least it was for when it was flown last week. I took it out today and had a little trouble getting it to run correctly. I started over by screwing the high end mixer all the way in and then came 2 1/2 turns out(which is what i have been told is a good place to start when adjusting an engine). When i start it here the engine will run a little rough and it spits out alot of smoke a fuel from the muffler. I then slowly start to turn the screw in(which if i'm not mistaking is supposed to richen the mixture). It will eventually run smooth and sounds as if it transitions well. I am really scared of tuning it too lean and damaging the engine, but at this setting it is still showing a good bit of smoke. My problem is when it gets here, i can start the engine and immediately rev it up and down with it transitioning well. I then drop the throttle and place the plane on the ground. It will taxi out to the launch area at about a quarter throttle, once i get in position i try and throttle up for takeoff and it will shut off(doesn't matter if i slowly throttle up or quick it will cut off). I don't hear any sputtering or anything before hand, it just shuts off. Do you think i still have the mix set to too rich? like i said, i'm really paranoid about making it too lean. Any help would be greatly appreciated. THANKS in advance everybody!

i had this problem on thursday.
what the problem (for me at least) was that on the test stand it would be a little rich. however when throttled for takeoff the forward movement of the plane would lean it out just enough to kill it.
richen it a little and see if that helps.
is that FP a airbleed carb? if so turning it in does richen it.
if it is a regular (dual needle) carb turning it out will richen it

It is still too rich

Don't be completely redoing the needle valve each time

Just check it before flight

The FP is usually user friendly