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My buddy bought a 2015 yz250 (brand new, we put about 30 hours on it).

Everytime he rides it he fouls a plug, EVERYTIME. So i thought maybe he mixed his oil wrong. He did a little more than usual but not enough for the plug to foul. I thought maybe jetting needs to be changed but I ride his bike every week as i store it on my land for him and I have never fouled a plug on it. I have more experience riding 2 strokes and dirtbikes in general so maybe his clutch game is the issue? He crashes the bike going down hill on the mx track and has had the "fear" holding him back ever since. When he does ride the bike you can hear the engine bog and struggle to haul him around and he putts around low revs all the way. 265 pound's he weighs.

All in all im curious what can i do to make this bike not struggle so hard and stop fouling plugs. Is there anything i CAN do?

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I would look up the YZ250 jetting chart and try to get the jetting right for the bike for the temp and altitude, playing with the pilot jet, main jet, and needle. I have never played with the power jet and have made my bike run a lot better adjusting the three I just described. 

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I order a jetting kit aswell just incase ( got to adjust the 92 2 stroke aswell) but i will do what you guys recomended aswell.

How would you go about getting the dude more comfortable on his bike after a crash? Just more practice hours?

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Uh I am 240 without gear. I have a yz125 that is jetted pretty rich. I even rode it at 11k feet last year with the same jetting. I have never fouled a plug. You can not constantly lug a 2 stroke at low rpm out of the power range. Jetting may help but he needs to either needs to learn to keep it in the power so it doesnt load up or buy a four stroke.

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Right? ive seem hige dudes putting small bikes just ripping them. Unfortunately i cant just tell him to stop being a pussy and fix all the problems. Maybe i should gear it down to make it less snappy so he doesnt shit himself. He definetly has whisky throttle syndrome.

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1 hour ago, mikedabike said:

 You can not constantly lug a 2 stroke at low rpm out of the power range. Jetting may help but he needs to either needs to learn to keep it in the power so it doesnt load up or buy a four stroke.

wrong , jetted right it will lug all day , and don't use high flash point oil if your riding slower

Edited by kxrob
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Yeah bad choice of words. Lugging is one thing but running rpm so low in a gear too high that the engine stuggles and bogs will foul plugs regardless of jetting.

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13 minutes ago, mikedabike said:

Yeah bad choice of words. Lugging is one thing but running rpm so low in a gear too high that the engine stuggles and bogs will foul plugs regardless of jetting.

Jetted right they'll run any way you want, all day.  Idling, lugging, wide open. 

Fouling plugs is almost entirely a matter of running excessively rich.  If the plug doesn't stay hot enough to self-clean it will load up on deposits and foul.  Varying load and engine speed will help if there is a specific range that is running rich and its okay elsewhere.  Fix that rich spot though and you won't have to worry about it.

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15 minutes ago, Renotherhino said:

Thoughts on gearing it down some teeth on the sprockets?

You'd probably be better off using a throttle tamer (check this out from G2).  Basically it takes more twist to raise the slide the same amount, protecting against whisky syndrome to a degree.

As far as the fouling, make sure it's got the right pilot jet in it for your location, and that the air screw is adjusted properly.  I've heard of some guys using a "7" (hotter) spark plug, but I don't think I'd go that route.  I'd go with kxrob's oil suggestion way before I tried that.

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As mentioned already here and in 100 other related threads, the correct fix for fouling plugs has nothing to do with how you ride the bike.

A 2 stroke with good design for broad power, like the current yz250, which is mechanically healthy and correctly tuned (incl spark and choke usage) won't foul plugs. It can idle or be lugged all day with 32:1 premix and still produce great power when required. Correct tuning means maximum power and no plug fouling.

You will probably both enjoy riding the bike more if you go one size smaller on the pilot jet.

If you want more fun then try a thinner cylinder base gasket. Stock is 0.6mm. 0.3mm are easy to find and will seal correctly if you thoroughly clean the mating surfaces. BUT beware of pinging with the increased compression and low quality fuel.

If you want predictable, linear roll on power without the 1/4 throttle blubber then the 3/8th lean bog, then you need to replace the yam needle with a Zook needle. Many other threads on that mod.

Edited by numroe
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Tell him to rev it a bit with the clutch pulled in so hes not gaining any speed once and a while when lugging it around to clear it out without going fast.

I run my yz a hair rich (stock jetting) as I ride some deep sand and open fire roads, to keep it from fouling a plug while riding slower single track or extreme enduro like stuff where I cant get on the pipe I clutch it and rev it to clear it out if I feel it loading up, its not as good as revving it out in gear but it works.

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