I have a 2001 Tomos Targa with biturbo exhaust, 27" front sprocket and I jetted it to 56 or 58. It ran fine all last year. This year I changed the oil. cleaned the carb, spark plug and air filter etc. It starts fine and runs good for about 5 minutes or so. If I keep the throttle at the same spot, around 3/4 to maximum I have a problem. It starts slowing down, starting to accelerate and then dies out. Sometimes I can save it by twisting the throttle back and forth. I have no probs restarting it. I tried adjusting the idle but no fix. any ideas???