A forum for owners of Yamaha TTR250 trail and enduro bikes!

 BUTCHER WROTE:

hi guys i took my TT-R 250 on its first long ride "under my ownership" and it was fluttering on high revs and wasnt performing well so i dicided to strip my carb down.. i had a 52.5 Mikuni pilot in there and a 140 main jet.. i consulted with a mechanic i know and he said my needle was too small for the jet.. (i've never heard that before) he gave me a 126 main jet and now the bike is moveing like a 250 but i can feel it isnt giving its all, what do i need to put that 140 back in

 Answer:A flathead screwdriver and an 8mm lol

Depending whether the spark plug is oily or not a black spark plug can mean it's running rich eg. (main jet # too big for set up) or worn rings or valve stem seals =blowing smoke=black spark plug??

If it's not blowing smoke on start up (while cold)or while running a black plug can mean you are running rich (ie main jet too big)but i don't see how that can be if using #140mm unless your air filter is blocked or or old

Note: White crust on spark plug means running lean

Steps to do

Clean pilot jet, main jet and carby spotless also making sure you clean the needle and seat (float needle)

Blow all holes out with an air compressor

Does'nt help?=drop the carby pin down one on the circlip holding the pin inside top of carby

Still does'nt help go up to #148mm main jet

If still not as desired go #150mm main jet and fit an aftermarket air filter eg K&N or similar and Fmf Q4 or similar

#50 mm pilot jet should be ok to use with any main jet mentioned as i'm using #150mm main jet + #50mm pilot jet and goes really well since i did the change from #147mm to #150mm main jet with an aftermarket air filter and trimmed the snorkel (air box duct)down a bit...Yet to get an fmf Q4 but run an xt 500 exhuast atm.

Note: YAMAHA made some models a small pethetic main jet eg.#140 -#147mm and under because of carbon emissions in some states,countries ect. It was to do with enduro events as they had to comply with strict rules and regulations.

Also to make the bike more managable for the novice riders

and the fact that the air box is'nt exactly a high flow box



Other note: It may be hard to get a #148mm main jet as i looked on the jetting info page eg. http://ttr250.activeboard.com/t49951533/jetting-information/ and it may not be common anymore May have to use #147 main

Remember: The bigger the jet the more air flow it will need to run properly ie .#150 main jet or higher=K&N filter+FMF Q4 or similar to get the most out of the bigger jet.

Jarrah.