RE: Engine tuning question
Chris,
Before meddling too long with the adjustments, see if there is anything restricting the fuel flow in the lines (clunk pressed against back of tank, fuel-line kinked, Etc.), or inside the carburettor...
If opening the needle does not causes the engine to run very rich, something else is limiting the flow of fuel.
Do not use a fuel-filter in the line between the fuel-tank and the engine!
If you cannot find anything in the fuel-lines, you may need to disassemble the carburettor, to clear the jets.
Before you do this, connect a piece of fuel-tubing to the carburettor nipple and turn the high-speed needle, to ascertain it has direct control over the amount of air you can blow through the nozzle.
You should feel the resistance to blowing decrease, as you open the needle up to 4-5 complete turns...
After making sure the entire fuel path is clear of any obstruction, check the adjustments.
Start way rich on both needles... A four-stroke engine cannot be run so rich that it would 'eight-cycle'...
Start the engine and slowly advance the throttle to full and there, start closing the high-speed needle, until peak RPM is reached.
If the engine begins to slow lean; closing the needle more may cause it to backfire and throw the prop!
Find peak and open the high-speed needle ~1/8 of a turn.
Make sure you can close the throttle to idle and return to full-throttle.
Then go to the low-speed needle and adjust it for ideal response/transition.