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Need help jetting 2017 yz250

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I have a 2017 yz250. It's been on 4 big rides now and no issues until yesterday. It is stock besides GYTR weighted flywheel. I lug the bike alot in the woods and I know it's jetted more for racing so I'm thinking that's the issue. Fouled 3 spark plugs yesterday in the woods on tight single track. I run 32:1 fuel ratio. Any help on jetting suggestions would be greatly appreciated. The only difference yesterday as opposed to other rides was the humidity. It was 85 degrees and very high humidity. Previous rides have been between 60-80 degrees

 

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The jetting stock is a little on the rich side to keep things safe.

I wouldn't mess with the jetting too much initially. I suspect you are not getting sufficient heat in the combustion chamber to keep the plug clean. I would suggest a BR7 or even a BR6 plug. The plug will run hotter as it is better insulated and resist fouling. If you are going to go on a ride where you will tapped out more, higher in the rpm range go back to the stock BR8 plug. If you leave the lower number plug in your will suffer detonation and possibly cause some top end damage.

I know a lot of enduro guys do this. Slightly rich jetting will give you a good bottom to mid range and keep temps down. But you need to compensate and run a plug that will clean itself.

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Thanks for the info. It also blows a lot of spooge out of the power valve drain hose. Will the plug help with that? Or jetting? I hardly ever have it wfo. We almost always ride tight single track. But yesterday was the first time it became an issue. 

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2 hours ago, Foxrider91 said:

I have a 2017 yz250. It's been on 4 big rides now and no issues until yesterday. It is stock besides GYTR weighted flywheel. I lug the bike alot in the woods and I know it's jetted more for racing so I'm thinking that's the issue. Fouled 3 spark plugs yesterday in the woods on tight single track. I run 32:1 fuel ratio. Any help on jetting suggestions would be greatly appreciated. The only difference yesterday as opposed to other rides was the humidity. It was 85 degrees and very high humidity. Previous rides have been between 60-80 degrees

 

search " jetting with zook needle " and you will get your answer

32:1 is not necessary for slower /trail riding no matter what the manual says

40:1 to 50:1 , 45 pilot , necj suzuki needle clip 3 ( also get a nedj needle and run clip 2 in summer ) , and do a plug chop for the main

look up spanky's jetting guide it explains a lot on correct pilot jet selection , air screw adjustment and how to do plug chops

factory jetting no matter what bike is rich and the dual taper yamaha needles leave a lot to be desired

should look at measuring your head squish as well and get that corrected

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Not trying to sould like an idiot but what is head squish and plug chop mean. I am pretty mechanically inclined and can rebuild carbs and dirt bikes just not sure what your talking about. 

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9 hours ago, Foxrider91 said:

Not trying to sould like an idiot but what is head squish and plug chop mean. I am pretty mechanically inclined and can rebuild carbs and dirt bikes just not sure what your talking about. 

Search it , it will become clearer 

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I would agree with all of the above replies. Try going 40:1 premix with a BR7ES plug (1 range hotter than stock, this wont cause ANY issues whatsoever..). You could also try dropping the pilot 1 size, say 48 if you are using the stock 50 now. This would help with the low speed riding you are doing and make it respond better and use less fuel. Wouldn't hurt to check the float level height while you have the carb apart also.

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Depends on elevtion with the jets but you can find charts that are pretty on for the yz. I would also suggest trying 40:1 unless your at the dunes or on the pipe hard constantly.

 

 

 

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I found a step by step process on how to check everything. I'm gonna go from a 50 to 48 pilot jet. I turned the air screw out until I got the highest idle and it was at 2.75 turns out. Says if it's less than 1 turn to go with a bigger pilot and if more than 2.5 turns to go with a smaller pilot. I'll lower the size then do the plug chop test to determine if I need to change my main. Thanks for all the info though.

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I found a step by step process on how to check everything. I'm gonna go from a 50 to 48 pilot jet. I turned the air screw out until I got the highest idle and it was at 2.75 turns out. Says if it's less than 1 turn to go with a bigger pilot and if more than 2.5 turns to go with a smaller pilot. I'll lower the size then do the plug chop test to determine if I need to change my main. Thanks for all the info though.

Hey fellow 250 rider how’d the jetting turn out ? I just bought a 2018 yz250 bone stock off the showroom floor . I rode it yesterday for the first time fouled one plug . I was on a very slow single track in 85 degrees with Indiana humidity. I’m running 32.1 fuel since it’s in the break in stage, all stock setting except I went from #50 to #48 . Air screw is around 1 1/4 turns . Seems to smoke a lot on idle and got spooge at the end of pipe . Maybe it’s just because the bikes new and I’m learning to ride ? I never did leave 2nd gear or really hit the power band much .

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On 5/28/2017 at 3:52 PM, kxrob said:

search " jetting with zook needle " and you will get your answer

32:1 is not necessary for slower /trail riding no matter what the manual says

40:1 to 50:1 , 45 pilot , necj suzuki needle clip 3 ( also get a nedj needle and run clip 2 in summer ) , and do a plug chop for the main

look up spanky's jetting guide it explains a lot on correct pilot jet selection , air screw adjustment and how to do plug chops

factory jetting no matter what bike is rich and the dual taper yamaha needles leave a lot to be desired

should look at measuring your head squish as well and get that corrected

what kxrob said, plus #8 slide, have the squish corrected, look up the thread on the #40 power jet, then ride it like you stole it!

Edited by yz dude

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I ende

On 9/16/2018 at 12:51 PM, Don Carrico said:


Hey fellow 250 rider how’d the jetting turn out ? I just bought a 2018 yz250 bone stock off the showroom floor . I rode it yesterday for the first time fouled one plug . I was on a very slow single track in 85 degrees with Indiana humidity. I’m running 32.1 fuel since it’s in the break in stage, all stock setting except I went from #50 to #48 . Air screw is around 1 1/4 turns . Seems to smoke a lot on idle and got spooge at the end of pipe . Maybe it’s just because the bikes new and I’m learning to ride ? I never did leave 2nd gear or really hit the power band much .

I ended up doing a ton to my 2017 yz before I got it where I wanted it. Sent the head to RB designs to correct the head squish. Best money spent. Running jd jet kit red needle in 2nd position, #168 main, #45 pilot, changed float height from 6.5 mm to 9 mm. Also installed vforce 3 reeds. It runs a ton better now. But every bike is different depending on your location. But I have no more spooge coming out of the power valve hose anymore and no more fouled plugs. Still running 32:1

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Someone could make a killing if they had a Jetting clinic. Bring the bike spend a day riding and tuning. I know I’d pay :)

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Even at 0-500 feet above sea level, you can safely drop 1 size main, 1 size pilot, and another 1/4-1/2 turn on the air screw,  (and i'm talking about using the bike on an MX track)  and that should make it run much better.

 

 

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Even at 0-500 feet above sea level, you can safely drop 1 size main, 1 size pilot, and another 1/4-1/2 turn on the air screw,  (and i'm talking about using the bike on an MX track)  and that should make it run much better.
 
 

I’m at 800 on average and 90 % single track woods. The only change I’ve made is pilot down to 48 . I did order a JD kit and Air screw for easier adjustments we’ll see how that works . I’m just trying to get that light brown electrode color . Everything above 1/4 theory seems good . Bike only has 2 hours on it so I’m hopeful it’ll get better with experience.

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