have a two stroke 1998 60 cranks idles great and will typically run perfect bout five to ten minutes until heats up the if get over about 2500 rpm it will skip u could say sounding like rev limiter or something wah wah sound but still continues to crank idles fine ect thought it was coils and replaced them was told change therostat and water pump but peas good carbs and fuel lines just redone but sat up long time what could it be maybe cdi but what are signs that is expensive troubleshooting any ideas