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Just picked up a new YZ250 a week or so ago I did my heat cycles and got it broke in. Its been at least 15years since I’ve been on a smoker been riding thumpers and just recently had a crf450. Its to the point I don’t have all the time for the proper maintenance on the 4ts so I went back to a 2t. I’m rusty on jetting and need you guys help as where to go I think the bike is running rich based on my plug in running a 32:1 mix as that is what I used to run I live and ride at sea level on the east coast. I’m not sure what the bike comes with stock as far as jetting but when I bought it it came with some jets. Can you guys help me out thanksIMG_1517167232.619346.jpgIMG_1517167246.528357.jpg

 

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Just picked up a new YZ250 a week or so ago I did my heat cycles and got it broke in. Its been at least 15years since I’ve been on a smoker been riding thumpers and just recently had a crf450. Its to the point I don’t have all the time for the proper maintenance on the 4ts so I went back to a 2t. I’m rusty on jetting and need you guys help as where to go I think the bike is running rich based on my plug in running a 32:1 mix as that is what I used to run I live and ride at sea level on the east coast. I’m not sure what the bike comes with stock as far as jetting but when I bought it it came with some jets. Can you guys help me out thanksIMG_1517167232.619346.thumb.jpg.8a1d34a5290363c9f4bec7da3fc8ffaf.jpgIMG_1517167246.528357.thumb.jpg.6bfa423584fc1e8357be113669282bd0.jpg
 


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First make sure the float height is set at the proper level,

it isn't unheard of that some bikes are mis-adjusted right off the showroom floor (my YZ125 was)

 

Second, if you are still getting used to riding a 2-stroke 'on the pipe' and

recreationally riding rather than racing, I suggest using a low flash point premix oil 

and not a fancy high temp 'racing' oil.  Moreso in cooler winter temps. 

 

Since it's a brand new bike, you no doubt also got a factory service manual included with it.

Take time to read it, there is likely a nice jetting chart and tuning suggestions mentioned in it.

 

Ideally the air screw is fine tuned daily for ambiant temperature and humidity changes.

Pilot jet and needle settings are best tuned by 'feel' (say idle to 3/4 throttle)

and only the main jet (3/4 to full throttle) can be judged by plug coloration.

 

Here"s a handy how-to: http://www.braigasen.com/howtoread.htm

Edited by mlatour
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First make sure the float height is set at the proper level,
it isn't unheard of that some bikes are mis-adjusted right off the showroom floor (my YZ125 was)
 
Second, if you are still getting used to riding a 2-stroke 'on the pipe' and
recreationally riding rather than racing, I suggest using a low flash point premix oil 
and not a fancy high temp 'racing' oil.  Moreso in cooler winter temps. 
 
Since it's a brand new bike, you no doubt also got a factory service manual included with it.
Take time to read it, there is likely a nice jetting chart and tuning suggestions mentioned in it.
 
Ideally the air screw is fine tuned daily for ambiant temperature and humidity changes.
Pilot jet and needle settings are best tuned by 'feel' (say idle to 3/4 throttle)
and only the main jet (3/4 to full throttle) can be judged by plug coloration.
 
Here"s a handy how-to: http://www.braigasen.com/howtoread.htm

Thanks man I’ll take a look

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Keep in mind the jetting chart in the service manual is for all-out motocross racing in mind.

 

Slower paced riding, either trail/off-road or moderate pace MX track can usually benefit 

going to slightly leaner pilot and needle settings than what the manual suggests.

 

As most time is spent riding on the needle circuit, in general:

Bog / revs pick up slowly = lean

Stutters / feels like hitting a rev limited = rich

Edited by mlatour
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Keep in mind the jetting chart in the service manual is for all-out motocross racing in mind.
 
Slower paced riding, either trail/off-road or moderate pace MX track can usually benefit 
going to slightly leaner pilot and needle settings than what the manual suggests.
 
As most time is spent riding on the needle circuit, in general:
Bog / revs pick up slowly = lean
Stutters / feels like hitting a rev limited = rich

Thanks for the advice I did notice when riding tight single tract woods it does seem to bog out of a tight corner and it is slow to come on. I have to clutch a lot to get the power to come on

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Well it is an MX race bike, you can't expect the same roll on torque as a 4T 450.

Perhaps a YZ250X (the off-road version) would have been better suited to your usage.

Edited by mlatour

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Check the float level and drop the main jet by one size. Worked great on my YZ250X for east coast sea level. 

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Well it is an MX race bike, you can't expect the same roll on torque as a 4T 450.
Perhaps a YZ250X (the off-road version) would have been better suited to your usage.

There wasn’t one for 150+ miles from my dealer. That’s what I was originally looking for. I’ve ridden 2strokes before but it’s been a long time I don’t expect the same tool on torque as a 450
Check the float level and drop the main jet by one size. Worked great on my YZ250X for east coast sea level. 

Thanks I’ll give it a try

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On 1/29/2018 at 3:20 PM, BigA92 said:


There wasn’t one for 150+ miles from my dealer. That’s what I was originally looking for. I’ve ridden 2strokes before but it’s been a long time I don’t expect the same tool on torque as a 450
Thanks I’ll give it a try

How did the jetting work out for you ? I also just got into 2 stroke with a 2018 yz250 all woods riding.

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How did the jetting work out for you ? I also just got into 2 stroke with a 2018 yz250 all woods riding.

Sorry for the late reply my phone isn’t letting me know when I have notifications. I started with adjusting my float height it was to high. Then I got the bike so so with the jets that came with it. Then I ordered a fmf gnarly pipe and a powercore silencer while I was ordering that I went ahead and got a J.D. jet kit and I went by their guide lines and got the bike pretty darn close. I have been riding most sundays and I keep tweaking here and there until I get it perfect

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Sorry for the late reply my phone isn’t letting me know when I have notifications. I started with adjusting my float height it was to high. Then I got the bike so so with the jets that came with it. Then I ordered a fmf gnarly pipe and a powercore silencer while I was ordering that I went ahead and got a J.D. jet kit and I went by their guide lines and got the bike pretty darn close. I have been riding most sundays and I keep tweaking here and there until I get it perfect

Thanks for the information. I’m pretty close with the stock jets and I also have a new JD kit on my bench . Just haven’t changed it yet for the simple fact I didn’t want to start over . I’m not changing anything else, keeping stock exhaust.

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On 1/29/2018 at 5:20 AM, BigA92 said:

 

Just picked up a new YZ250 a week or so ago I did my heat cycles and got it broke in. Its been at least 15years since I’ve been on a smoker been riding thumpers and just recently had a crf450. Its to the point I don’t have all the time for the proper maintenance on the 4ts so I went back to a 2t. I’m rusty on jetting and need you guys help as where to go I think the bike is running rich based on my plug in running a 32:1 mix as that is what I used to run I live and ride at sea level on the east coast. I’m not sure what the bike comes with stock as far as jetting but when I bought it it came with some jets. Can you guys help me out thanksIMG_1517167232.619346.jpgIMG_1517167246.528357.jpg

 

 

search for jetting with zook needle on the yamaha forum

google spanky's jetting guide

 

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see Klinger 317’s thread on the power jet 40

 

it is curious two of you bought the MX bike to ride woods. I drive 150 miles round trip to get to woods trails, so I would have easily driven further than that to buy the X version I wanted. Too late now, but there are other mods you can do to make the MX version better in the woods. Easily found in this forum. Throttle cam and flywheel are common examples.

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