bogging down

[smiffy123uk]

hello; i have a 1999 yz125 which is bogging down off idle it ticks over fine but when i want to set off it wants to stall for a second or too then it seems fine once it is in motion i presume it needs new jets but not sure whether it will need both main and pilot jet or just pilot plus not sure whether to go smaller or bigger so any advice would be great the bike is standard except for rear silencer which is a fmf power core 2 shorty cheers

[cr2504life]

I dont' know alot about jetting but it sounds like you could be lean. I would problay go up one size on the pilot. Before you do anything wait for some others to respond.

[steiner]

how long have you had the bike.

[easyas123]

If the bike idles fine then the pilot jet is fine.
The main jet takes over from 1/3 to fully open throttle.
You may have some trash in the main jet i also have a 99 yz 250
and from stock it has a 172 main jet and the air screw should be any where to 1 to 1 1/2 turns out from the closed position.
Take a look at the plug to see if it is white or black it should be a golden brown color black indicates fuel fouled , white means too lean.If you have alot of oil running out of the silencer try going to 40 to 1 mixture if oil still runs out go down in jet sizes remember oil and gas is mixed together in 2 strokes if its too rich you will have alot of oil running out the silencer and alot of smoke.

[Faded]

Originally posted by easyas123
The main jet takes over from 1/3 to fully open throttle.

Easy there easy...there are a couple of other things responsible for jetting between the pilot and the main...

The first thing to do is start by making 100% sure that there are no problems mechanically (read: check your reeds) before automatically assuming it's jetting. The jetting should be the last resort when trying to solve problems that just pop out of no where.

[smiffy123uk]

hmm i changed my fuel to super unleaded 97 ron and reduced my mixture to 36:1 and she seems to be a lot better im gonna go out again this weekend and see how she does

[02mncr250]

When was the last time you did a top end in the bike?

[smiffy123uk]

i havnt yet i have a saying dont fix what isnt broke, she starts first kick every time and goes like s**t off a stick

[smiffy123uk]

oh yeah i only had the bike a couple of months i dont race,i ride just purely for fun on an old quarry once every week so i dont give it that much stick