2017 YZ250 no top end rev

Tony_Clements
Edited Date/Time 1/4/2020 8:46am
Bought new but old stock and bike has only 36 hrs and had top end at 27. This problem occurred out of the blue mid race. Bike starts and runs perfect up to where it refuses to rev out. I cleaned out the carb best i could at the track but same. Had carb apart on the bench and was spotless but blew everything clean with an airline anyway. Same. Read about sliencer issues but it's clear with no rattles and I even pushed a hose through it without problems. P/V works if I move the arm not sure if there are other issues to check with it. Readng about stator problems there always seem to be popping, missing, type issues but up to the point it stops revving it runs spot on. I might be able to borrow a donor bike to swap parts but want the least risk to messing up another bike. CDI will be simplest to switch followed by coil and stator is bottom of my want to switch list. Anything else it could be. Thx for reading.
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FGR01
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FGR01 12/31/2019 8:13am
12/31/2019 8:13am
Try a new plug.

Check the reeds.

I'd try swapping the complete carb from the other bike so you can at least rule out or narrow it down to the carb.

Then try swapping the complete tank and cap from the other bike. Might be a clogged petcock screen or gas cap vent.

There is a pin in the power valve governor mechanism that can break and that will prevent the power valve from opening. This would coincide with the sudden onset you experienced. You can check the PV operation by removing the pipe and then the right cylinder cover. Reinstall the pipe and rev the bike on the stand to observe full travel.

While you have the pipe off, inspect the inside of the pipe and silencer core for excessive carbon buildup. Especially if you run any kind of castor oil.


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cwtoyota
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cwtoyota 12/31/2019 8:24am
12/31/2019 8:24am
Tony_Clements wrote:
Bought new but old stock and bike has only 36 hrs and had top end at 27. This problem occurred out of the blue mid race...
Bought new but old stock and bike has only 36 hrs and had top end at 27. This problem occurred out of the blue mid race. Bike starts and runs perfect up to where it refuses to rev out. I cleaned out the carb best i could at the track but same. Had carb apart on the bench and was spotless but blew everything clean with an airline anyway. Same. Read about sliencer issues but it's clear with no rattles and I even pushed a hose through it without problems. P/V works if I move the arm not sure if there are other issues to check with it. Readng about stator problems there always seem to be popping, missing, type issues but up to the point it stops revving it runs spot on. I might be able to borrow a donor bike to swap parts but want the least risk to messing up another bike. CDI will be simplest to switch followed by coil and stator is bottom of my want to switch list. Anything else it could be. Thx for reading.
My buddy had a 2013 model that did something like this. The sound from the exhaust would change to a lower tone as if the exhaust was clogged and the bike just wouldn't rev past maybe 1/3 of it's normal RPM range.

I thought it was possible that his issue had something to do with the CDI unit and the 2011 change where they added the shift position sensor.

In 2011 the USA model of the YZ250 got the shift position sensor and a different CDI unit as well as that massive silencer. My understanding is that feature changes the ignition timing when the bike is in neutral. It's just a clever way for the bike to meet more strict global sound regulations.

His problem was intermittent, it would run like that at start-up and be stuck in that state for a bit. If he shut the bike off and started it back up it would still be in that weird state. Randomly it would go back to running normally.

We tried my 2010 and 2002 CDI units on his bike when it was running that way and it ran perfectly with the older ECUs. If you have a donor bike, try swapping CDI modules between them.
Tony_Clements 12/31/2019 9:32am
12/31/2019 9:32am Edited Date/Time 12/31/2019 9:37am
Thx for the advice guys. I did try the plug, 2 in fact. I did also blow through the tank vent and the tap is full flow. The bike is pretty much like new so pipe and exhuast are clean as was the carb. Trying with the P/V cover off seems an easy test to start with. I presume me moving it manually won't happen automatically if that pin is toast. I will try swapping the carb second. It worries me playing with other peoples electronics so is a last resort but looks like it will be the only way if those fail. The bit that confuses me is it's perfect to start and revs cleanly. Feels like diesel to race as just stops revving at a set point and goes flat. I'll let you know what I find the weekend although if in a fit state might try with the P/V cover removed tomorrow.
slipdog
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slipdog 12/31/2019 12:37pm
12/31/2019 12:37pm
Rare, but I have seen the exhaust bridge crack and the main exhaust valve gets stuck closed. Since it's actuated off a spring the pv arm and sub valves still open and look like everything is fine if you take the cover off to check. Runs great on the stand but put it in gear and it goes flat mid rpm

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FGR01
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FGR01 12/31/2019 9:46pm
12/31/2019 9:46pm
slipdog wrote:
Rare, but I have seen the exhaust bridge crack and the main exhaust valve gets stuck closed. Since it's actuated off a spring the pv arm...
Rare, but I have seen the exhaust bridge crack and the main exhaust valve gets stuck closed. Since it's actuated off a spring the pv arm and sub valves still open and look like everything is fine if you take the cover off to check. Runs great on the stand but put it in gear and it goes flat mid rpm
Yep, and even more common with the same symptoms/result - the lifter mechanism for the center valve gets worn/sloppy over time and either the spring or the pin breaks off. Same effect, mechanism moves but center valve does not lift open. Hopefully this didn't happen on a clean bike with only 36 hrs.


Tony_Clements 1/1/2020 1:47am
1/1/2020 1:47am
I survived new year so later today I will try running the bike without the P/V cover to see what happens and if there is movement. As I said if the arm is moved manually I can see the P/V moving. Having had the carb apart twice I will wait for the donor bike and try the whole carb as an wasy way to check if it's the issue. Obviously the only way to test the bike, other than the visual movement of the P/V, is to ride it. That won't happen until the weekend so I will let you know the results when I do. Thx again
Tony_Clements 1/1/2020 5:04am
1/1/2020 5:04am Edited Date/Time 1/1/2020 7:06am
Well i warmed her up for as short a time as i dared so I could rev it with upsetting the neighbours too much. No movement of the arm so I got braver and revved some more. How many revs before it opens? Unless you have to scream it somethings gone. I may have to wait for the other bike and do the same test for comparison.

Update. Got the donor bike so ran that up with the cover off and it seems you don't need to rev it that much for the arm to move. Need to dismantle the whole thing and check what's happened. The pin, as suggested, looks like a prime suspect.
FGR01
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FGR01 1/1/2020 8:20am
1/1/2020 8:20am
I think you've really homed in on the problem here.....ooooffff!
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Tony_Clements 1/1/2020 11:07am
1/1/2020 11:07am


Made a mess of this bolt but I think the thread it goes into is reclaimable with a tap to clean it up.
PTECH
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PTECH 1/1/2020 4:55pm
1/1/2020 4:55pm
Tony_Clements wrote:
[img]https://p.vitalmx.com/photos/forums/2020/01/01/395414/s1200_yz_pv_bolt.jpg[/img] Made a mess of this bolt but I think the thread it goes into is reclaimable with a tap to clean it up.


Made a mess of this bolt but I think the thread it goes into is reclaimable with a tap to clean it up.
You figure out what tried to escape from inside your engine yet?
FGR01
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FGR01 1/1/2020 7:59pm
1/1/2020 7:59pm
Is that the center bolt that holds the primary gear on the crank? Kinda looks like that bolt backed out based on the crack in the case cover.
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DynoDan22
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DynoDan22 1/1/2020 9:26pm
1/1/2020 9:26pm
Yamaha has had a known issue with the primary bolts backing off and blowing out the side case. When this happens, the auxiliary primary gear (not the main primary gear that drives the clutch basket but a thin gear on top of the main primary) comes off the crank spline and you lose drive to the PV governor and water pump. I believe that's why your PV isn't opening as you've lost drive to the governor. It scares my how many primary gear bolts I've seen come loose. I personally have repaired three. I can't believe Yamaha hasn't found a solution to this it's been going on since '00 to current on the 250's.
Tony_Clements 1/2/2020 2:59am
1/2/2020 2:59am
Exactly what it is and what happened. The case is saveable as not bad enough to even leak yet. I will clean the female thread hopefully as apparently it's M8 1.25 and I have that tap somewhere. Finding the bolt in stock was a nightmare despite it fitting several street bikes as well. Having found one they are closed for stock taking until Sat, mobile number worked, so will be at the shop early.
I take it loctite isn't a cure then? Maybe I will use the red stuff and heat it to remove when I have to.
sandman768
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sandman768 1/2/2020 3:14am
1/2/2020 3:14am
Tony_Clements wrote:
Exactly what it is and what happened. The case is saveable as not bad enough to even leak yet. I will clean the female thread hopefully...
Exactly what it is and what happened. The case is saveable as not bad enough to even leak yet. I will clean the female thread hopefully as apparently it's M8 1.25 and I have that tap somewhere. Finding the bolt in stock was a nightmare despite it fitting several street bikes as well. Having found one they are closed for stock taking until Sat, mobile number worked, so will be at the shop early.
I take it loctite isn't a cure then? Maybe I will use the red stuff and heat it to remove when I have to.
red loc tite for sure! Had this happen on one of my bikes, not a YZ but results the same.

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DynoDan22
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DynoDan22 1/2/2020 6:18am
1/2/2020 6:18am
Red loctite for sure. Glad your case is still useable.
Tony_Clements 1/2/2020 9:17am
1/2/2020 9:17am
Picking up the bolt Sat morning. Had stuff on today but will give the case and the female thread the once over Fri. Not perfect for a new bike but could have been way worse.
DynoDan22
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DynoDan22 1/2/2020 9:19am
1/2/2020 9:19am
Yeah, sucks to happen on a newer bike. I see you're in Fontucky! I'm just up the hill from you! haha
Tony_Clements 1/2/2020 9:45am
1/2/2020 9:45am Edited Date/Time 1/3/2020 12:38am
DynoDan22 wrote:
Yeah, sucks to happen on a newer bike. I see you're in Fontucky! I'm just up the hill from you! haha
I'm not unfortunately, that would make life much easier with so many stores to choose from We vacation the area to ride. Proride Phil has a bunch of our stuff living in his garage in Fontana. Not been out a while, this will be the third year missing it, but will be back for 2021 en masse. At least that is the plan.
Compare to Socal and add £3 shipping

Part Stock Qty Price
YZ250 – CLUTCH
BOLT, FLANGE
90105-10445
BACKORDER
NO STOCK
1 ×
£7.76 £7.76

Less than $4 stateside.
Tony_Clements 1/4/2020 7:54am
1/4/2020 7:54am
Bought a tap to  clean the thread on the crank and with loads of loctite a new bolt is fitted. Managed to clean up the old bolt for an emergency fix if ever needed. Ran up with the cover off and all seems to work fine including the water pump. Test ride tomorow. If it happens to you stop riding immediately. It will save you a bolt and more importantly a case. You should be able to fix it at the track if caught early as no damage will be done to the bolt or thread hopefully.  if I buy a new one I will loctite before I use it.
Blackjack31
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Blackjack31 1/4/2020 8:22am
1/4/2020 8:22am
I don’t have this problem but all I ride is Yamahas and would like to know which bolt you are talking about because I will be replacing everything in the motor this winter. This is the bolt that threads the primary gear onto the crank? That bolt should have red loc tite? Is that correct?
Tony_Clements 1/4/2020 8:43am
1/4/2020 8:43am Edited Date/Time 1/4/2020 8:45am
Blackjack31 wrote:
[img]https://p.vitalmx.com/photos/forums/2020/01/04/396143/s1200_D9A98BCB_5F74_4813_B9F5_D2082159F3BD.jpg[/img]

Thats the one. Manual doesn't mention loctite. I was tempted to use red but smothered it in blue and will check it after a few rides. Now I know the sympton I will be parked the second it ever happened again.
Part number 5: BOLT, WASHER BASED 90105-10445-00 $4.55
https://www.bikebandit.com/oem-parts/2017-yamaha-yz250-yz250h2/o/m15918…
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Blackjack31
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Blackjack31 1/4/2020 8:46am
1/4/2020 8:46am
Tony_Clements wrote:
Thats the one. Manual doesn't mention loctite. I was tempted to use red but smothered it in blue and will check it after a few rides...
Thats the one. Manual doesn't mention loctite. I was tempted to use red but smothered it in blue and will check it after a few rides. Now I know the sympton I will be parked the second it ever happened again.
Part number 5: BOLT, WASHER BASED 90105-10445-00 $4.55
https://www.bikebandit.com/oem-parts/2017-yamaha-yz250-yz250h2/o/m15918…
Thank you. I’ll be sure to throw some blue on it. Yeah, red seems a little much. I think blue will be fine.
lorensolara 4/22/2023 1:00am
4/22/2023 1:00am

This same thing happened to me just a week ago now my governor gear doesnt fit on the crank

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