[QUOTE=jeffie8696;12073549]Im confused. My brand new Surpass getting broke in on the test stand. Needle settings rich, 15% champion fuel, OS F plug, Even though it will run decent and transition well it surges at the higher rpms. And the idle while reasonable is not smooth. I have tried different plugs, prop, fuel and nothing. It will surge regardless of needle setting both high and low. I have taken off the carb and sealed the mating surfaces , disassembled the carb and checked for blockages. Even checked the cam to be sure its in right and the lash on the rockers.[/QUO

I really don't know OS 4S, but maybe the crankcase vent system is clogged or not working. Just a thought, I don't even know what that would cause. Good luck. But, be careful, don't void the warranty.
Sincerely, Richard
AMA 861960
Club Saito #635; Saito 56, 100, 120abc, 130T, 180
YS F 120; OS 15, 25, 40, 46, 60, 61, 80