Any ideas on how to adjust the carb etc on the Robin 4hp engine for the Manco Thunderbird so that it does not sorta hesitate at top speed? Once you reach top speed, it feels like it wants to go faster then backs off and it keeps sorta hesitating. I'm guessing it's something with the idle? It's a brand new carb I installed and I did not make any adjustments as I am not sure which screw does what? Also a new Spark plug which came pretty much already w/ correct gap. Any suggestions would be great. TIA