More Fuel Problems

[racerdad33]

My son is riding a 2002 Yam yz125 with a completely fresh new top end and stock except for v-force ram valve and pc pipe/silencer.Problem is we can't seem to ever get the thing jetted rich enough.We are now running ngk br10eg plug riding on tracks in Arkansas and Texas w/490 main jet.We used to run straight Turbo blue fuel and plug stayed too white and went to a mixture of 50/50 w/ pump gas and made it a little richer but not much.My question is I see a lot of guys at the track who have to blow there bikes out before they ride them but ours cant sit and idle for 2 minutes and then just go like a four banger would lol.Maybe we just need to go bigger with main but 490 is quite big for a 125 I thought.Son rides hard as hell on the gas too.Any info would be appreciated.

 

[bclapham]

did you actually cut open the plug and look for the "ring"? some race fuels burn clean and dont much leave colour on the plug. also, have you checked for airleaks making it run lean?? deto marks on the head and piston????

btw- as my mate marcus says, Jet the bike not the theory- so if it needs a 490 then try it. my rm144 is supposed to run richh on the pilot and lean on the main- i can find a pilot small enough, ive got the lenaest needle and with a 460 main it was detoing bad enought to vibrate the plug loose.