porting and main jet

[jamman]

If my 98 YZ125 has been ported by a shop, how much richer should I go on the main jet?
The rest of the bike is completly stock except for the Boyesen Rad valve that we have yet to install. Any chance in the porting and Rad valve cancelling eachother out and just leaving the stock jet in there! That would sure make things easy. Lol

[369DuneBunny]

i can't give you a number for jets. but i see what ur saying about the reeds cancelling out the porting.

but even tho u jet down for reeds it's alot more minimal than upjetting for porting

[jamman]

thanks DuneBunny, I'm getting closer. Boyesen says to go 1-2 sizes leaner for the Rad valve. Do you think plus 10 would be close for porting? I've tried writing to the company with their name stamped on the side, but no response. I don't wanna buy like 20 different jets. I was hoping I could get her dialed within half that amount! Lol All's I know is she bogs on the bottom and explodes on top. If I drive like a sissy it fouls within 10-15 mins. Drive it hard, and it could go for weeks before fouling.

[369DuneBunny]

since porting on a d.b. jug is probably less intense than on a quad cyl cuz dirtbikes are usually hogged out stock... i think +10 is a good place to start.

if you paid for a wilder port start richer and lean it out.

if you have a keihin carb i've noticed that ktm dealers are the cheapest on hex jets. i dunno for mikunis

[jamman]

Right on, I'm gonna take the carb apart tomorrow and try to pick up a few bigger jets and work my way down from +10. Thanks for the KTM tip too!

[flotek]

theres only so much that can be done on this bike,i have a pretty good idea where you would end up on my porting but youll have ot ask the guy who did yours and see his recommendation, he should know ,if he doesnt then he has no business porting it imho