What size jet

[crev]

I have an 85 Honda 250R. with 40 over piston fmf pipe. race ported cylinder ( top end ). stock reed cage. no air box, k&n 6inch air filter. want to put 39mm carb on. what size jets should I start with.

[Samjp22]

IMO id upgrade your reed cage as well, I've got basically the same mods as you and have a 39mm PWK on there right now I've got a 42 pilot jet and a 175 main. With the cold weather and fresh top end its still a little too lean for my liking. Elevation here is around 500m, don't know what it is there and weather wise I don't know either bud id say start with the 42 pilot and like a 165 main. I also have my needle clip on the last notch

[crev]

Thanks that's a place to start