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Dirt Bike Discussions By Brand
Yamaha MX & Off-Road Dirt Bikes
Jetting on TTR125
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[QUOTE="Idaho Charley, post: 124073, member: 19246"] Don't have a Yamaha part number for the pilot jet. If you look in your owner's service manual on page 4-4 the pilot jet I mentioned is item number 15 located adjacent to (i.e. recessed hole) the main jet. Just remove it and take it to any place that stocks Mikuni carb parts and ask for the next size up. You may even want to buy the next two sizes up (17.5 and 20). Install the new pilot jet and warm up the bike; then adjust the pilot air screw identified as item 18 on page 4-4. Although the pilot air screw is somewhat of a pain to get to I just made a small straight screw driver tool (about 2 inches long) from a piece of 1/8 inch welding rod. i.e. touched one end to a grinder on opposite sides and then clipped the rod to the length I needed. Reach in and tune away. I start with the air pilot screw open about one and 1/2 turns and try to find the adjustment which gives the fastest slow idle then I turn the air screw in 1/4 of a turn: It just seem that the throttle response off idle is better when I do this. My boy's bike can now come off the choke much sooner without bogging or killing the motor under a light load. Also starts with 2 or 3 kicks when cold where before we were stroking maybe 12-15 times before it would light-up. BTW - Noted that a number of the posts seem to indicate that their bikes would not rev out. After making our initial mods - air box, opening the snorkel, etc. our bike would also studder at high rpm and not run clean. I verified there was no rpm limiter via the dealer and then went ahead with a plug check. Plug check indicated rich on the main, so we went down in sizes until it ran clean which was with a 100 main and I could likely go to a 97.5 main. Just to clairify we do ride at much higher elevations (5000ft) than many of you and we have not gone with an after market pipe which can drastrically change jetting. The bike really revs and we have not noticed any valve float or any sort of studder at high rpms; the bike just builds power to a peak then power tapers off (bike is screaming) and it is pass time to shift. Hope this helps!! [/QUOTE]
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Dirt Bike Discussions By Brand
Yamaha MX & Off-Road Dirt Bikes
Jetting on TTR125
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