Ken,

I have done quite a few of these engines and they are pretty solid.

I have always done exactly what the book tells you to do.

The way to tell between 2 and 4 stroke sound is this. Before starting, turn the needle valve clockwise until it seats but do not force it, then open the needle valve turning it counter-clockwise about 3 full turns and start the engine. Once it starts wait about 30 seconds for it to warm up and take it to full throttle. At this point the engine will be spitting fuel and making allot of smoke and if you listen closely it also sounds as if it is missing which it actually is because it is only firing on every other stroke (4-cycle operation) and it most likely will be vibrating allot, now start closing the needle valve until the engine starts to pick up rpm's which will be about 1 to 1 1/2 turns and when you hear the sound change to a high pitch scream and the rpm's increase allot, that's when it's running in 2-cycle operation. All of the above is based on adjusting the high speed needle valve.

If you cannot tell the difference in sound then a tach will help allot.

After running 4 tanks through it, doing the above will not help that much as long as you did it with it spiting lots of fuel from the exhaust you should be OK.

Once you have the breakin completed, refuel the plane, close the needle valve and reopen it to about 1 1/2 turns and start the engine, now lean it but turning the needle clockwise and listen closely and you will hear the rpm's increase, once they stop increasing stop leaning the needle and turn it counter-clockwise about 1/4 turn, you are looking to get max rpm by leaning it then you richen it to loose approx. 300 to 500 rpm beacuse when you fly it will lean out on it's own in the air. Now go fly. After about 4 flights you will needle to readjust the high speed once more and start working on the low speed needle.

The low speed needle on these engines is for setting the mixture from idle to mid-throttle and has everything to do with the transition from low speed to high speed and how quickly and smoothly that happens.

The low speed needle is a very small screw inside the hole where the throttle connection is on the right side of the carb (looking from the cockpit forward) and never ever try to adjust it with the engine running.

To adjust the low speed first make sure the high speed is set as described above (max rpm minus 300 - 500 rpm, this must be done first), then start the engine and blip the throttle quickly from idle to half throttle. If the engine stumbles (hesitates) and spits fuel and smoke then picks up rpm then the low speed is too rich. (The low speed needle is somewhat sensitive), you need to turn the screw clockwise (lean) only 1/8 of a turn. Now if the engine stumbles and hesitates and picks up rpms quickly then dies without spitting fuel and smoke you will need to turn the low speed counter-clockwise to richen it again only turning it 1/8 turn. Once you adjust the low speed retest it to make sure.

Once you have finished the low speed then verify that going from idle to high speed quickly is working good. Once you move the throttle from idle to full throttle quickly, the engine should immediately go to full throttle without stumbling, hesitating or it dying. Do this also to half throttle to verify the low speed.

You should be able to do all of the needle settings as described above in less than one tank of fuel. Keep at it as that is a great engine and you will love it. I recommend an 11X5 or 11X6 or an 11X7 prop for that engine as long as the plane has the ground clearance for it.

OS normally sets the low speed a little rich at the factory so it will usually take about a 1/4 total turn lean to get it to run and transition well.

I do the half throttle thing to confirm the results to full throttle as the low speed needle handles the mixture from idle to half throttle then at which point the high speed needle takes over.

enjoy