Yz 250 Flywheel weight

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#1
A friend of mine recently bought a 88 Yz 250. The previous owner added a Flywheel weight. Will a flywheel weight cause the bike to Idle weird? The Bike just doesnt respond the way it should from the bottom. Jetting is perfect. The bike pulls real good mid to top, just of the bottom it takes it a little while to build up rpm`s.
I`ve heard the weights help in trail riding because you can lug the bike more. Is this true?
 
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#2
we removed the flywheel weight on an 00 kx250. it does rev faster. flywheel weights have many benefits, we just removed it to see what would happen and liked it.
 
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#4
It would be a good idea to pull the carb out/tear it down/clean it completely/record all the jet #s etc. 2 strokes just love it when you do this for them!! It doesn't take much crud in a carb to screw up a smooth running motor. just take your time doing it and remember-"NO parts left over on this rebuild!!"
 
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#6
Well Fuzzy thats what I thought at first but after performing several throttle chops on a few different plugs it sure looked good to us. The carb is clean, and the reeds look good. The only thing left to do is take it off and see how she does. If its not welded on. havent looked at that yet.

Thanks for all the help.
 

fuzzy

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#8
Yes, a WOT plug chop will test your MAIN jet. Try adjusting that little thing called an air screw outward. If it get's better, but not 'best' than install a leaner pilot. Then look at needles, slide leaning, etc. There is a lot more to jetting then the 'test' you performed. The 88 YZ motor should pull off bottom very smooth with good power, hit in the midrange like crazy, and fall off a bit on top.

A FWW will make it rev slower, but will also retain crisp throttle response. Less flywheel weight will also have crappy throttle response with bad jetting.

The FWW will make the bike harder to stall when lugging around in the woods as well as proving better traction in slippery conditions. They are generally used for woods riding, not moto-x. The weight will help with the sharp midrange of the YZ motor.
 
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#9
Thanks for all the tips! Dont know what to tell you! Jetting looks good.
Messed with the air screw till my fingers where raw. Tried a smaller pilot and went throught the needle slots. Still idles weird and responds slow till about 3/8 throttle. Screw it as long as it runs. He`ll just have to hold it wide open.

What I meant with throttle chop was that I checked the jetting Ericlachance.
Does that " INLIGHT" you my friend?
 
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#10
do you mean you did a throttle chop to check the condition of the pilot circuit? Cause if you did, that might be your problem. You can only determin the condition of the main jet by doing a throttle chop...
 
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#11
oh, yeah, you cant do a throttle chop with a brand new plug either... I still think the pilot or slide might be the problem... As for the flywheel weight, I have a 12 oz weight on my 96 yz 250 and still have instant throttle response using 94 octane pump gas...
 

Rcannon

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#12
Originally posted by ericlachance
oh, yeah, you cant do a throttle chop with a brand new plug either... I still think the pilot or slide might be the problem... As for the flywheel weight, I have a 12 oz weight on my 96 yz 250 and still have instant throttle response using 94 octane pump gas...
 

Eric, your not kidding. I added the same weight to my 97 YZ. Do you get the feeling that these bikes should have been shipped from Japan with the weight?  No one that rode my bike before and after prefered it without the weight.
 

OKKX'er

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#13
Your description sounds just like my '00 KX250 with the flywheel weight. I like the bike much better w/o the weight. It really slowed the low rpm response without any benefits I could notice.
 
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#14
i really like the weight. It still has incredible throttle response, but the weight seems to make the midrange hit less violent... Plus, i find it really does improve traction. Less wheel spin.(wheelies on command!). i really do like it. i would probably of prefered a thread on weight as opposed to a welde on weight, that way, I could of changed it depending on conditions an the way i use the bike (a little more for trails, a little less for mx) but All in all, I'm a happy camper.

Eric