The Sullivan Megatron starter (Tower Hobbies) will crank up to 110cc gassers with no problems.
http://www3.towerhobbies.com/cgi-bin...&I=LXADJ2&P=ML
Need to hook it up to 24v to have adequate cranking power. I use 2 lawnmower batteries from Wallmart for $25 bucks each and hook them up in series for 24v.
It's worth the investment if you're getting into big gassers. Need to use a car starter modified for RC use if you're cranking 150cc monsters though.