2001 WR250F Bog Thread (have searched but have many questions)

Hello folks, looking for some help from the guys the really know the WR250F.
Bit of back story, my brother bought a used WR250F (2001). Great little bike, slightly on the heavy side but perfect in most other ways (incredible suspension, fast and fun, and so far reliable too).
Don't know the hours on the bike but it was in good shape and seemed fairly low (bough from a guy on a farm who just used to rip it around his property).

So the bike has run pretty good since we've had it the past season and a half and quite happy overall no issues.
Cold starts are rough, but once you get her running then starts 2nd to 3rd kick pretty much.
Also once you run the bike after riding it when you turn it off the carb would piss a little gas from the carb for a few seconds after turning it off.
While riding was mint anywhere from 1/4 or 1/2 throttle and above is super peppy and really pulls hard, surprisingly this bike really goes fast and powerful and with the really good suspension I love ripping this thing.
Off idle it has the dreaded bog, and I've read about it and experience it first hand quite frequently when I try my brothers bike.
I am able to compensate while riding by getting revs up and dumping clutch to do quick maneuvers, but my brother is a little less experienced and struggles some times with the bog when we get into more tight technical riding.

Both my brother and I have 2 young children/babies a piece and my carb tuning days are on hold for the time being since hands full with my 2 wild babies.
We decided hey lets take the bike to the pro's and dropped it off at a local shop that came recommended.
The ask was, can you slightly tune the carb to see if you can improve the bog. Also asked to true a front wheel.

Got it back a week later and they said they put and o-ring kit and putting it all to stock jetting. Also they true-d the front wheel.
They said we can't ride it without the snorkel which apparently has already been removed (as in we didn't have one in our bike and they said they'd sell us a used one if one of the tech could find it).
Brought it home and after 100 kicks couldn't start it (cool evening weather).
Next day tried and tried, and on a whim while trying to cold start it I tried the hot start and boom 2nd kick.
Tried it like that again and same thing 2nd kick, and that was strange (not sure it should be starting from a cold start using the hot start on the carb).
But when running the bog is now so bad if you give throttle off idle it pretty much bogs and sputters off. Way worse than before and not bike won't even stay running.
Also it's running SO HOT it over heated in just a few minutes of letting it idle, and in our experience the bike has never overheated since we've owned it (even on the hottest 36Celcius humid days in tight forest single track and never got too hot or overheated).

So we are now stuck with a bike that went from 80% to un-usable after taking it to the shop.
My brother is an expert sheet metal installer and we found the specs and size/pictures of the snorkel and made one ourselves out of aluminum and installed it and tried it with the stock jetting the shop said they installed, and it did not change at all, still has same issues running too hot, and sputters with even worse bog than before. Shop was adamnet when they gave us the bike that the snorkel will solve everything. $400 later bike can't be used.
I asked my brother to call the guys and ask what they took out and if we can get it all back maybe we can re-install the previous jetting and try to tune it ourselves or get the JD kit.

Couple of things to note about the bike now that I'm reading up on things specific to the WR; we had no snorkel in the bike and shop claimed jetted way too rich but wouldn't say what jets, also there is a white wire connector on the carb side slightly above the carb (think 2 prong) that is left disconnected and I'm assuming this is the YZ or grey wire mod as they call it? The bike has the stock exhaust and airbox looks un-modified. We run only Shell 91 and ride around 800 feet above sea level most of the time and can get quite hot and very humid here in southern Ontario.

My questions are:
- with stock jetting will the snorkel get the bike back to normal as the shop is suggesting?
- has there been a definitive fix identified for the bog?
- what is the recommended jetting for around 500-1000 feet above sea level?
- how can I tell if the AP squirt mod is already done?
- how can I tell if the exhaust baffle has already been modified?
- would it be best to just work from scratch with a JD jet kit a this point and re-confirm all the necessary free mods are done?
- is there a recommended spark plug to use on this bike?

This is what I'm thinking of getting plus the fuel mixture screw.

Sorry to resurrect this ongoing and frequently discussed issue.
There is so much info about it and all scattered and just really hoping some very experience folks might be able to give some insight and advice here.
Thanks for reading and thanks for any info or help with this.
Cheers and happy riding!


Edited by Serialize

Approach each issue one at a time and in sequence.

First, the hard starting/idle

Check the pilot jet size, it should be a 45. Confirm the fuel screw is there and is correctly assembled. Setting should be around 1.75 turns from gently closed.  You may want to check the float height per the manual.Also, confirm the shop put the vacuum release plate in properly. Cold bike should always need the choke to start (even on a hot day) and the hot start after an extended period of slow riding with the engine super hot OR possibly after a crash due to flooding.

The extended fuel screw you selected is a good one.

Once the idle issue is fixed, (and you can do this during the time you have the float bowl off) check the leak jet size. Stock is #709 or larger, which is great for a racer, not so great for a trail rider. Buy a 45 or a 50 leak jet. Check the diaphragm and make sure it is in good shape. Be careful to install it facing the right way. Do not lose the oring.

The snorkel only affects operation above 3/4 throttle.

Wires to the carb should be connected, that is the TPS. The TPS should be set per the manual. The wire that should be cut/removed is the gray wire to the CDI though most do not notice the slight change in throttle 'sharpness'.

The shop is clueless. Get a OEM service manual and set all up per it. The exception being the smaller leak jet (and extended fuel screw). The JD kit works well though you are just as well off buying a NYCS Yamaha needle and an oring (378 plumbers oring) for the AP.


Thanks for the reply and info William1.
Im going to call the shop on my brothers behalf and find out what's all in there, find out if we can get our previous hardware back also.
We though hey spend the $400 and get it all done for us but guess I'm gonna have to tear it all out myself and figure out whats going on.

Shop said they put to what manual spec should be for jetting, will have to confirm what that is.
Then like you said I could try different leak jet and start from there.

Sorry to ask this, and I'm sorry will sound stupid but what are all the carb components I should check off the list when I call the shop?
- pilot jet
- primary/main jet
- secondary jet
- leak jet (new term for me could be one of the above)?
- needle
- clip and clip position
- diaphragm
- AR
- Snorkel
- TPS position

Anything else I should be asking about?

Thanks again really appreciate the feedback and help.

6 minutes ago, Serialize said:

Sorry to ask this, and I'm sorry will sound stupid but what are all the carb components I should check off the list when I call the shop?
- pilot jet
- primary/main jet
- secondary jet
- leak jet (new term for me could be one of the above)?
- needle
- clip and clip position
- diaphragm
- AR
- Snorkel
- TPS position

Anything else I should be asking about?

Thanks again really appreciate the feedback and help.

I doubt they messed with much and any that they changed, should be listed on the repair order. But...

Get a service manual. They can be D/L here: http://www.yamahaownershandbook.com.au/lib/download.php?f=5PH-28199-30.pdf

Read it before you do anything.

Pilot jet and main jet might of been changed. Needle clip position as well. Everything else should of been checked and serviced as called for but... it sounds like the shop is not the best place so I'd start with the service manual, take your time, and go though the carb. Parts like the pilot jet, I suggest buying a brand new #45 (cost about $5, not worth hoping it is good).

With no snorkel, at most, it needs a larger main but that only matters once you get about 9,000 rpm and at 7/8ths and above throttle, close to flat out.


I have an 01 as well.  The PO of my bike wired the accelerator pump lever to the throttle so it is in constant contact, and I went down to a 45 leak jet after the fact.  No bog ever.  As for the lack of starting, check your idle mixture adjustment first.

Thanks everyone for the replies and info.
It's going back to the shop today, my brother called and they said it's in not running right to bring it in.
Will see where we end up and whether I will have to tune it when we get it back.
Really appreciate all the feedback.

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