sprocketspecialists.com will take care of trailprotrailpro 13/39 set up i have talked to one guy with this set up and says he would never go back to the 42 that his r performs very well "to much" power on the bottom-end, also he said it gives u alittle more ground clearence, doesnt really matter u will still be runnin the stock skid plate, go dg full exhaust system, i have seen one of these run be4 and it plain out HAULED! (steph) it also had the 85R carb on it, u can use a v-force reed valve on a air-cooled also and would tell u to go that way, i have a rad valve on my air-cooled and really cant tell that much difference and have been told its basically a stock reed cage with bigger reed "ports" or where the reeds go, v-force is a totally different reed valve and is highly recommended by most high performance engine builders, also use a reed spacer those will give u alittle more torque for trailprotrailpro sprocket choice but still give u the most out of trailprotrailpro performance. i have a 1/4 inch spacer on mine and love it.
adam
86 ATC 500R the duner..
85 ATC 500R...the not quite finished faster duner
1985 ATC 250R Bone stock!!
1985 ATC250R mx/duner
1986 TRX370R MX/Duner
94 Banshee 400PV Cheetah 105RWHP