kennyg1

I have a older , used Surpass 91 which is giving me grief. When the idle screw is set as per start point ( 2 1/2 - 3 turns ) motor won't run. The only setting which works is , idle screw 5 turns and high speed needle 1 turn . It is very rich BUT goes high to low without hesitation . It will also SOMETIMES stop suddenly ( at 3/4 to full rpm ) . When I open carb , fuel runs out > even with idle screw turn in to 1 1/2 turns. Tank is set as per req. 1/4" above center of barrel . The same settings are req. sitting upright on my test stand or inverted in my plane . ( although fuel seems to run out of carb more inverted) The clearence on valves is set correct and compression feels good .The high speed needle has a SLIGHT bend but seems to settle in concentric to axis once its screwed in 1/2 to 3/4 of the way. Can anyone diagnose these symptoms ?
Thanks in advance .

Bax

My Feedback: (11)

Without seeing the engine, it's difficult to determine the problem. We don't rely on number of turns, so the number doesn't mean much to us, especially on the idle mixture setting. We start out with both high-speed and idle needles too rich. Get the engine runnng at full throttle and lean to just rich of peak RPM, then retard the throttle and work on the idle mixture.

If the high-speed needle's bent a bit, then it will affect tuning. 3/4-turn is in a bit too much. Normally, we'd see a setting somewhere near 1-1/2 turns out from closed +/- 1/4-turn or so. Many problems are caused by a bad needle seat. If it's been eroded a bit, the high-speed needle has to be turned in to help meter fuel. The only solution is to replace the carb body and high-speed needle.