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Jetting the 2017 Mikuni carb

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I just got my new 250 xc w. It's jetted really fat and now that it's broken in I want to re-jet. I am trying to avoid getting a handful of jets and taking a day to hopefully get it right.  Has anyone tuned new Mikuni?.  I'm in Florida, (sea level) Any help will be appreciated.

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Boatload of info in the KTM 2 stroke section. Lots of opinions on the tuning. JD Jetting is the fast track to satisfaction. Can go further and much better results fixing a cruddy OEM reed cage/reeds.

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I put the JD kit on mine and looped the overflow hose on it runs great,I bought the vforce reed valve just to be on the safe side for petals breaking but do not feel any difference in running.

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With any luck, maybe you guys can chase the OP away. He already stated his newby status. 

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16 hours ago, DEMI said:

With any luck, maybe you guys can chase the OP away. He already stated his newby status. 

Baptism by fire. Its best to find out what your getting into sooner than later. 

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1 minute ago, GreenMT_Rider said:

Baptism by fire. Its best to find out what your getting into sooner than later. 

He already did with me, no need to pile on. But if it makes people feel better, then so be it.

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Are we talking about a the 17' or 18' model ?  The biggest problem with the Mikuni carbs that come on these bikes is the overly rich #4 slide that comes on these bikes. These bikes really needs at a min, 5.5 slide or the slightly leaner #6 slide. If you own a 17' it will also need a richer s-4 needle jet. I believe, but am not certain that the 18' bikes, 250/300 come with an S-4 needle jet already installed. Once you have the S-4 and #6 slide you'll be into an oem 42-74 needle in the 3rd or 2nd clip position along with a 440 main and a 30 pilot jet, to start out with. IMO, the leaner slide in particular is  critical in correcting the carburation in the Mikuni carb, but in needs to be combined with the richer s-4 needle jet.

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11 hours ago, rtv said:

Are we talking about a the 17' or 18' model ?  The biggest problem with the Mikuni carbs that come on these bikes is the overly rich #4 slide that comes on these bikes. These bikes really needs at a min, 5.5 slide or the slightly leaner #6 slide. If you own a 17' it will also need a richer s-4 needle jet. I believe, but am not certain that the 18' bikes, 250/300 come with an S-4 needle jet already installed. Once you have the S-4 and #6 slide you'll be into an oem 42-74 needle in the 3rd or 2nd clip position along with a 440 main and a 30 pilot jet, to start out with. IMO, the leaner slide in particular is  critical in correcting the carburation in the Mikuni carb, but in needs to be combined with the richer s-4 needle jet.

Naaah......my '17 has been running VERY well for the last year with only the JD kit installed. Simple

 

 

Joe

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I have had zero issues with the performance of my 17 300XCW over the year that I've owned it. I'm not happy with the fuel range, but unlike a zillion redundant threads on the Internet, my bike runs great. The float height was off from the factory, the dealer fixed it when I bought it in for the brake reservoir recall. Stock is not a problem.

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9 hours ago, trailmeisterjoe said:

Naaah......my '17 has been running VERY well for the last year with only the JD kit installed. Simple

 

 

Joe

JD himself, doesn't use his own kit with the stock #4 slide and stock needle jet.  I believe he also uses a #6 slide with an s-4 needle jet and   his own jet needles in his 17' 300.

Edited by rtv
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Unless you have a lot of spare time and nothing to do just buy the JD kit and ride. I wasted so much time dicking with that carb I threw in the towel and installed the JD kit. Haven't touched the carb since, 

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JD needle myself in the 17 250xc. Blue needle 3rd clip, 440 main and a 30 pilot with 92 ethanol free at 55:1 . Out of all the ktms i had with the Keihin carbs the mikuni is every bit as good with excellent fuel economy.  I'm extremely picky when it comes to jetting.  I have no problems swapping carbs out if im not happy. I can say im very happy with the jetting and the mikuni carb 

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15 hours ago, rtv said:

JD himself, doesn't use his own kit with the stock #4 slide and stock needle jet.  I believe he also uses a #6 slide with an s-4 needle jet and   his own jet needles in his 17' 300.

Nope......incorrect. He uses the stock slide and needle jet. He has experimented with them of course because he is in the jetting business.

 

 

Joe

11 hours ago, GreenMT_Rider said:

JD needle myself in the 17 250xc. Blue needle 3rd clip, 440 main and a 30 pilot with 92 ethanol free at 55:1 . Out of all the ktms i had with the Keihin carbs the mikuni is every bit as good with excellent fuel economy.  I'm extremely picky when it comes to jetting.  I have no problems swapping carbs out if im not happy. I can say im very happy with the jetting and the mikuni carb 

I can attest to Don's carb swapping ways LOL

 

Joe

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4 minutes ago, trailmeisterjoe said:

Nope......incorrect. He uses the stock slide and needle jet. He has experimented with them of course because he is in the jetting business.

 

 

Joe

I can attest to Don's carb swapping ways LOL

 

Joe

84 IT490 with a Keihin 39mm PWK,  and a 85 cr250r with a Keihin 36mm short body air striker off a ktm. Both bike run really good. 

20170729_152450.jpg

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16 hours ago, GreenMT_Rider said:

84 IT490 with a Keihin 39mm PWK,  and a 85 cr250r with a Keihin 36mm short body air striker off a ktm. Both bike run really good. 

20170729_152450.jpg

The ways of a prolific carb swapper being documented again here folks. 

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