Stuck at a dead end... YZ250

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11/3/2018 5:28 PM

So took my yz out for its 1st ride since I added new dry side crank seal, reed gasket, stator cover gasket to try and solve my surging issue while im riding. It stopped doing it like it had been before where it didnt take 10 minutes and it would do it really bad. I noticed today though it did it “off an on” but very little/slighty noticable as in I would ring it out and pull the clutch in and it would kinda do it till i fully pulled the lever to the bar and then sometimes it wouldnt do anything. Also found my idle to be kinda higher than it was previously so i turned it down and got it right. It was cooler than normal like in the 50-60s vs 70-80s.

Also found my clutch to be acting kinda weird as well. Hitting neutral and cant find neutral. Normally I never had an issue. I do constsntly use the clutch out of kind of a bad habit (which i need to break) so i started thinking could my clutch be going out since when i pull the lever where it disengages it may not be fully disengaging causing the weird rpm surging noise?

Other than 2 issues/annoyances the bike runs flawless and has power to the moon and back... im just lost here as i dont know what else to try. Ive done leak downs (cant get a good accurate reading cause my powervslve seal leaks), replaced parts.... someone give me suggestions.


Thanks guys....

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11/3/2018 6:05 PM

Id start with fixing your powervalve seal and ANYTHING ELSE wrong wjth the bike

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11/3/2018 6:09 PM

kb228 wrote:

Id start with fixing your powervalve seal and ANYTHING ELSE wrong wjth the bike

Nothing else is wrong with the bike besides these 2 things which i cant figure out. Also to fix my pv seal it requires a new cylinder or a bushing pressed into the pv hole so it wont round it out again. My cylinder is in perfect shape and next complete rebuild i planned on getting a new one to fix that. It doesnt leak either just leak down is skewed.

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11/3/2018 6:14 PM

What year YZ250?

What jetting is in the bike?

What fuel, oil, and ratio are you running?

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Powerband in every gear !

11/3/2018 6:17 PM

FGR01 wrote:

What year YZ250?

What jetting is in the bike?

What fuel, oil, and ratio are you running?

2010
48 Pilot
175 Main
1350-2600’
93 (Plus) Pump Gas/Spectro Gold/40:1

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11/3/2018 6:19 PM

If it leaks during a leak test then it leaks when running.
Have you checked the squish. That bike is know for squish issues.

Paw Paw

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11/3/2018 6:23 PM

Paw Paw 271 wrote:

If it leaks during a leak test then it leaks when running.
Have you checked the squish. That bike is know for squish issues.

Paw Paw

So my problem could be the pv seal letting air in then since thats the only thing that i know leaks as a while back i had a spot where premix ran down the case from running way rich. So i just have to deal with the little bit of rpm surging till i get a new cylinder or get that bushing and new seal?

I havent had it checked since ive had the bike.

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11/3/2018 7:36 PM

I'd also try swapping carbs with a known good bike. There are a few things in the YZ250 PWK carb that are difficult to diagnose that can cause funky symptoms like this. Also, a leaking wet-side crank seal can make the bike run very lean.

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Powerband in every gear !

11/4/2018 3:25 AM

I had a yz250 that developed a crack on the Ignition side case all around the crank bearing pocket, it took a while to find it, pressurize the engine & spray soapy water all over the engine....look up leak down test on utube...

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11/4/2018 9:31 AM

Make sure your gas cap is venting. You should be able to blow into it with little resistance but you should not be able to pull anything back.

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The older I get, the faster I was.

11/4/2018 9:50 AM

sandman768 wrote:

I had a yz250 that developed a crack on the Ignition side case all around the crank bearing pocket, it took a while to find it, pressurize the engine & spray soapy water all over the engine....look up leak down test on utube...

Mine has 2 patches of jb weld on the ignition side where it threw a chain at some point. Next full rebuild im buying a nee case half and a cylinder

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11/4/2018 12:29 PM
Edited Date/Time: 11/4/2018 12:43 PM

Start it and start giving small squirts of WD40 around seals/gaskets. When it reeves you squirted the leak.

Main crank bearings next to the seal have and up and down play? Should be zero.

Good seal on the pipe flange area? I use a slight coating of silicone sealant to make sure.

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11/4/2018 12:47 PM

lumpy790 wrote:

Start it and start giving small squirts of WD40 around seals/gaskets. When it reeves you squirted the leak.

Main crank bearings next to the seal have and up and down play? Should be zero.

Good seal on the pipe flange area? I use a slight coating of silicone sealant to make sure.

I just did that very thing and nothing. When i had the flywheel off i checked up and down play and checked clutch side as well. Sounds crazy but could the throttle cable where it goes into the top of the carb cause this issue? Ive taken carb off a few times and the cable can do a full 90 degree bend. Only thing on my bike that i know for sure leaks is the pv seal because when my bike was jetted super rich it made a spot around the cover on top of the case. Remembering now when I would go slower and than get on it for a bit and coast it happened more. Going up hills and putting it under load it would do the “surging” thing as well. Reason im at a loss because it doesnt make sense to me one bit.... i just wish i had a for sure answer instead of replacing parts and throwing money at it.

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11/4/2018 9:16 PM

If you have a leak around the power valve, it sounds like you already know what the issue is.. Order a new cylinder and seal and fix it correctly. You’ll continue chasing issues that don’t exist and continue wasting money if you don’t fix it what you already know is wrong.

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2017 RMZ450
2005 YZ250-sold :,(
1998 YZ250
2005 KX250F

80% of the time it works every time
IG @hammerfamily_4 & @2HRacing
Thanks to : Factory Effex, N2Dirt, Acerbis, DT1, Fasthouse, Matix, FMF, ASV, 100% & Mika Metals

11/5/2018 6:26 AM

mattyhamz2 wrote:

If you have a leak around the power valve, it sounds like you already know what the issue is.. Order a new cylinder and seal and fix it correctly. You’ll continue chasing issues that don’t exist and continue wasting money if you don’t fix it what you already know is wrong.

The left side case is pretty beat as well where it threw a chain before i bought it. Next complete rebuild im buying a new stator side case and new oem cylinder

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11/5/2018 11:37 AM
Edited Date/Time: 11/5/2018 11:40 AM

Please explain how a power valve seal could cause a lean condition? A YZ 125 & 250 both have a Power valve that has an atmospheric breather hose that lets air in and out of the power valve chamber.

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11/5/2018 11:47 AM

mattyhamz2 wrote:

If you have a leak around the power valve, it sounds like you already know what the issue is.. Order a new cylinder and seal and fix it correctly. You’ll continue chasing issues that don’t exist and continue wasting money if you don’t fix it what you already know is wrong.

Alec138 wrote:

The left side case is pretty beat as well where it threw a chain before i bought it. Next complete rebuild im buying a new stator side case and new oem cylinder

I say fix those issues first, then you can figure out the rest. Otherwise you will continue chasing your tail

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2017 RMZ450
2005 YZ250-sold :,(
1998 YZ250
2005 KX250F

80% of the time it works every time
IG @hammerfamily_4 & @2HRacing
Thanks to : Factory Effex, N2Dirt, Acerbis, DT1, Fasthouse, Matix, FMF, ASV, 100% & Mika Metals