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Jet needle question?

By 150ron,
in Motorcycle Jetting & Fuel Injection

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Grand Master

150ron

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Bike is a 09 yamaha xt250 4 stroke, i just put in a bigger main jet, (from #135 to a #140) opened up the air box, and am waiting on a FMF exhaust (did drill out the stock exhaust plate tho), i heard that richening up the jet needle has been good for some people and gives the bike more mid range pull/power.

So i removed my jet needle just now, but came to find out that it has no adjustments for the c clip, just one slot, so i added a small shim/washer underneath to raise it up a bit,

does it look like i raised it up too much, or just about right,

this is what it was before, just the c clip and a white nylon washer under it

xt32.jpg

and with my added washer

xt33.jpg

just hoping to get a bit more power, as the #140 main jet allready feels like it pulls stronger.

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Grand Master

jayc250x

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just hoping to get a bit more power, as the #140 main jet allready feels like it pulls stronger.

Please read one of the many articles on how to jet for a better understanding about what you are doing. The main jet primarily affects operation when your throttle position is 3/4 - WFO, so you'll only feel the effects of your main jet changes when the throttle is pinned. The needle position affects operation when the throttle is 1/4-3/4 open. Since most folks ride most of the time in the 1/4-1/2 throttle position, the needle clip position is the most important jetting tweak.

Alright - the space between needle clip slots positions are generally about the same as the slot itself. Your spacer is HUGE - way to big. You want to find small metal washers that are about as thick as the clip itself, then add two (2) washers to simulate moving up one clip position.

The little metal washer in your picture might be close all by itself.

Also, if the #135 is a stock main jet, with an opened airbox, you may want to try going bigger than a #140. I could be mistaken, but I'd guess that you'd need at least a #150, if not bigger.

Oh yea, forget the FMF exhaust and put that insert back in. Loud bikes suck and loud exhausts do NOT make more power.

JayC

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Grand Master

150ron

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Check out this thread, it will answer a lot of your questions. Pay attention to the plug chop stuff.

https://www.thumpertalk.com/forum/showthread.php?t=1026116&highlight=plug+chop

Here's another

https://www.thumpertalk.com/forum/showthread.php?t=1028599&highlight=

Thanks for the links. :bonk:

Please read one of the many articles on how to jet for a better understanding about what you are doing. The main jet primarily affects operation when your throttle position is 3/4 - WFO, so you'll only feel the effects of your main jet changes when the throttle is pinned. The needle position affects operation when the throttle is 1/4-3/4 open. Since most folks ride most of the time in the 1/4-1/2 throttle position, the needle clip position is the most important jetting tweak.

Alright - the space between needle clip slots positions are generally about the same as the slot itself. Your spacer is HUGE - way to big. You want to find small metal washers that are about as thick as the clip itself, then add two (2) washers to simulate moving up one clip position.

The little metal washer in your picture might be close all by itself.

Also, if the #135 is a stock main jet, with an opened airbox, you may want to try going bigger than a #140. I could be mistaken, but I'd guess that you'd need at least a #150, if not bigger.

Oh yea, forget the FMF exhaust and put that insert back in. Loud bikes suck and loud exhausts do NOT make more power.

JayC

Thanks for the responce, thats basically what i wanted to know, since my needle did not have different slots for the c clip, i had no clue (first time doing this also), so i figured that black washer i found was small enough, but if you think its way too big, i can always remove it and shave it down to half its size. ?

i understand how it operates now

0-1/4 = pilot/fuel screw got that one covered i think, bike starts up pretty good.

1/4-3/4 = needle jet, thats what im trying to accomplish now, to make sure its running to its optimum performance i guess

3/4- full = main jet, which seems to be running pretty good right now, no stumble or hesitation at all, just a nice strong pull.

The bike is not a power house, but its plenty for me,

ill take it for a ride, if it seems to stumble or hesitate in the 1/4 -3/4 range then my shim is too big and i need to go smaller right?

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Grand Master

Craigo

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Partly cover your air intake, If it runs better in your 1/4 to 3/4 range, it is lean on the needle...if this is the case you would raise the needle to make it richer....

Though a stumble is usually associated with too much fuel...I am not familiar with your model....Is there a way of temporarily making you air intake larger,cos if it runs better with more air it is running rich and then you would need to lower the needle...

It's easy increase the air with a DRZ400, you can just remove a sidecover,which makes up part of it's airbox...

You really should wait til you get your new pipe fitted before fine tuning your jetting...

Edited by CraigoDRZ400sm
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Grand Master

150ron

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Partly cover your air intake, If it runs better in your 1/4 to 3/4 range, it is lean on the needle...if this is the case you would raise the needle to make it richer....

Though a stumble is usually associated with too much fuel...I am not familiar with your model....Is there a way of temporarily making you air intake larger,cos if it runs better with more air it is running rich and then you would need to lower the needle...

It's easy increase the air with a DRZ400, you can just remove a sidecover,which makes up part of it's airbox...

You really should wait til you get your new pipe fitted before fine tuning your jetting...

ok, great info here. :bonk:

thanks

i just took it out for a 20 mile run, to test it out, and in this one 3 mile slight hill, before it would only go 71mph max, and now it went 74mph, so that was better, and the bike seem to get up to speed quicker in the /4 -3/4 range, so im pretty satisfied with this free quick mod. ?:banana:

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Grand Master

150ron

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Usually raising those fixed emissions needles won't make them richer where they need to be richer. If it doesn't work for you consider removing .010-.020 from the straight portion of the needle if you have the ability.

It seems to get up to speed faster now, so im happy with the results.

The spacer/washer i used is black plastic, will that be ok in there with the gas?

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