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Really had it....free bike anyone?


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i have really just about had it with this 1999 YZ 250...

im really about to set the POS on fire.

compression is perfect

plugs tried: BR9EG, BR8EG, BR8ES

my jets: 172 (standard), and 50 (standard)

mods: fmf gold series

it started out, where when it idles...it would surge (lean?)

once i took it for a ride, the first time i floored it...it would bog...then eventually kick in, and all was well. ran perfect after that...

after 2-3 rides of bogging the first acceleration...it would foul a plug.

got annoying.

i changed both side crank seals, the problem still continued.

i adjusted my float height, 3x....and now whenever i start it up, it revs TO THE MOON despite fiddling with the air/pilot screw.

i give up guys

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i have really just about had it with this 1999 YZ 250...

im really about to set the POS on fire.

compression is perfect

plugs tried: BR9EG, BR8EG, BR8ES

my jets: 172 (standard), and 50 (standard)

mods: fmf gold series

it started out, where when it idles...it would surge (lean?)

once i took it for a ride, the first time i floored it...it would bog...then eventually kick in, and all was well. ran perfect after that...

after 2-3 rides of bogging the first acceleration...it would foul a plug.

got annoying.

i changed both side crank seals, the problem still continued.

i adjusted my float height, 3x....and now whenever i start it up, it revs TO THE MOON despite fiddling with the air/pilot screw.

i give up guys

I'll come pick it up just let me know:smirk:
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Sometimes the extreme revving is caused by the Throttle position sensor. When I deconstructed my YZ and rebuilt it I didnt position the TPS correctly and that would cause it to rev to the point I thought it would blow the motor in less than 5 seconds. I looked at it for a bit and realized my TPS was angled alot differently than when I took it off so I repositioned it and problem solved

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when you set the float height, do you hold the carb at a 45 degree angle to see if it on the money? If it revs to the moon, you might have an air leak.

yes, it looks like originally it was set to around 8mm

i set it to 6, and it revved to the moon

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sykal where are you from in NY?

do not give up.

have u checked the TPS?

i am in yorktown heights (westchester county)

are you referring to that little white plug-in sensor?

its plugged in, not sure what you guys mean by if its in the right position tho...

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Assuming your throttle cable is routed well and is in good condition, I would open up the carb and take the top off where the slide is located and check to make sure the spring and clip are seated the correct way on the 6mm? small bolt that holds the needle in place. Should be a notch to align in there. Thats just a possibility

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Are you sure the throttle cable isn't pinched, frayed, pulled part way out, or otherwise damaged? If the throttle slide really is setting down on the idle screw and still reving up than you are pulling air from somewhere else, carb boot, reed cage t cylinder, base gasket, crank seal, crankcase center juntion, etc.

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just puled the top of the carb off, everything looks fine

there is some space where it settles down that i can see thru the intake end of the carb, but it all looks fine.

no holes in the boot either.

this crazy high reving just happened when i tried to set the float, so i dunno what it could be.

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Make sure you have at least some play in the throttle cable.

Also have you inspected the reeds?

The 125 I bought recently had a corner broken off one of the reed petals

and the bike would either fall on its face or rev to the moon.

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i am in yorktown heights (westchester county)

are you referring to that little white plug-in sensor?

its plugged in, not sure what you guys mean by if its in the right position tho...

take it to the yamaha dealer in new rochelle.

let him deal with it.

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I'm with MX86 on this, don't think the 99' has a TPS, it does have a power jet and I suspect that's where Sykal's confusion comes from. As he does have an electrical connector for the power jet solenoid but nothing for a TPS. I don't think he has an idle screw for the slide to rest on either as the 99' came with a Keihin PWM. http://www.partshark.com/fiche_section_detail.asp?section=35232&category=Motorcycles&make=YAMAHA&year=1999&fveh=902

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Does the slide sit in the fully closed/seated postion with the throttle closed? Verify this - you can actually hear if it does not close properly. If not, the throttle cable needs adjustment or a new one. It is 11 years old and you've fuddled with it so it could be stretched.

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Does the slide sit in the fully closed/seated postion with the throttle closed? Verify this - you can actually hear if it does not close properly. If not, the throttle cable needs adjustment or a new one. It is 11 years old and you've fuddled with it so it could be stretched.

when i let off the throttle, (with motor off), i can see the slide come down, and almost click...but there is def space that i can see so the slide is really not ALL the way down

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when i let off the throttle, (with motor off), i can see the slide come down, and almost click...but there is def space that i can see so the slide is really not ALL the way down

a small space is intended for idle but if it leaves like 1/4 of the slide travel area open your cable/spring is hosed.

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Seen these symtoms several times in different sports..

Two possibilities from my jet ski days (very similar two stroke, all the same)-

An Air leak is most probable-

Cracked Reeds-

From my dirtbike times-

Melted Crank stuffers(plastic fillers on crank) that cause the plugs to foul because they get plastic coating on them, and the bogging because the ring gets stuck/loss of compression until it heats up...very odd one to see coming

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