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 08 XT250 Exhaust Uncork & Jetting Mod
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lil_mynx
Ohio

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USA
25 Posts

Posted on 01/29/2009 at 3:59:35 PM  Member Profile  Reply with Quote
250f canuck, I hope it doesn't come to that. I had a hard enough time drilling the exhaust.

Glenn, Are you sure how the sizing is done? You and 250f canuck may just have come up with the answer.

08 XT250 "Because he told me not to buy it"
08 XR650l HorseRider650
07 CRF80 My Boys'
Tech: XT250 Exhaust Uncork, XT250 Mixture Screw Plug Removal, XT250 Tool Kit Retaining Screw

GlennF
Newbury, OH

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USA
501 Posts

Posted on 01/29/2009 at 4:29:28 PM  Member Profile  Visit GlennF's Homepage  Reply with Quote
I will do some research to be sure of the ratio of jet numbers to actual hole diameters. I am going to take an old jet that is numbered (i.e. Mikuni) and gauge the inside diameter with small drills. I should come close to an accurate relationship.I know I read this somewhere in a jetting forum. I will keep you all posted.

05 XT225 - Dunlop 606 front, Kenda 760 rear, Promoto Billet rack, fuel screw 3 turns out, 130 main, 42.5 pilot, Z1 exhaust mod, 1/2 snorkel, UNI filter, Bill's footpegs.

250f canuck
Super Tuner

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Canada
2213 Posts

Posted on 01/29/2009 at 5:17:02 PM  Member Profile  Click to see 250f canuck's MSN Messenger address  Reply with Quote
I'm pretty sure that's how jets are sized, the number on the side is a percentage of one millimetre. So a #34 pilot jet has a hole diameter of 0.34mm like Glenn said.

It shouldn't be that hard to drill the jet out, brass is a very easy material to machine.




01 WR250F - with lots of goodies

GlennF
Newbury, OH

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USA
501 Posts

Posted on 01/30/2009 at 08:07:30 AM  Member Profile  Visit GlennF's Homepage  Reply with Quote
I measured a Mikuni #130 jet and found a #55 drill (.052") just fit. That calculates to 1.32mm. The jet numbers represent 100ths of a millimeter. Drilling them out is still tricky.

05 XT225 - Dunlop 606 front, Kenda 760 rear, Promoto Billet rack, fuel screw 3 turns out, 130 main, 42.5 pilot, Z1 exhaust mod, 1/2 snorkel, UNI filter, Bill's footpegs.

GlennF
Newbury, OH

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USA
501 Posts

Posted on 01/31/2009 at 08:32:50 AM  Member Profile  Visit GlennF's Homepage  Reply with Quote
Here are some figures on drilling out the stock jets:

The problem is going to be drilling the pilot jet. The #34 pilot is .34mm which is equivalent to a #80 drill (.0135") This is a very small (jewelers)?) drill. The next size up is a #79 drill which is .0145" or .3683 mm or equivalent to a #37 pilot jet. That might be a small enough step to work. The main is a #135 or 1.35mm which is equal to a #55 drill. The next size up would be a #56 drill which is 1.367mm or a #137 jet.

05 XT225 - Dunlop 606 front, Kenda 760 rear, Promoto Billet rack, fuel screw 3 turns out, 130 main, 42.5 pilot, Z1 exhaust mod, 1/2 snorkel, UNI filter, Bill's footpegs.

ahilis
Lexington, KY

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USA
10 Posts

Posted on 07/07/2009 at 07:40:00 AM  Member Profile  Reply with Quote
quote:
Originally posted by HorseRider650

Admin, I talked to lil_mynx and she told me it was worth the risk to disassemble the carb to find out. So over the weekend she'll give it a try at her first carb tear down. My weekend should be fun.

Here is a break down (diagram) of the new carb for the XT250. You can notice that Yamaha is using a new electrical warm up circuit(lower emissions) parts 24-26. This is one step before carbs are done away with altogether.

It's interesting that the Japanese version, the Serow 250, has fuel injection and claims 18hp at 7,500rpm....


08 XT250 - Scorpion A/Ts w/ oversized rear; multiple small holes in muffler baffle; upside-down air filter cap

slopoke
Yucaipa, CA

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USA
12 Posts

Posted on 07/10/2009 at 10:12:46 PM  Member Profile  Reply with Quote
I tried drilling the jets, even one step larger induced a momentary choking hesitation when releasing full throttle. It's a little spooky on this bike at 80mph when the motor hiccups.

2008 XT250XC - mixture screw plug removed, exhaust uncorked, airbox modded, 45T rear sprocket, Avon Distanzias

mikebike
Deventer

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Netherlands
4 Posts

Posted on 07/23/2009 at 11:10:14 AM  Member Profile  Reply with Quote
Hello,here`s Mike frome Holland
I have a Tricker,XG250..a great thing
I have a GPR exhaust on it,and i wanna go for a open air box&filter,but now i wanna change the jets,and that is a big problem,is there someone who now`s what size off jet?
It most be a Keihin jet, that`s what i now,the 99 101 393
My bike:
Shot with Panasonic DMC-TZ3 at 2009-07-07

Aprillia SR 150
Yamaha Tricker XG 250

mikebike
Deventer

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Netherlands
4 Posts

Posted on 07/23/2009 at 11:25:29 AM  Member Profile  Reply with Quote
quote:
Originally posted by GlennF

Here are some figures on drilling out the stock jets:

The problem is going to be drilling the pilot jet. The #34 pilot is .34mm which is equivalent to a #80 drill (.0135") This is a very small (jewelers)?) drill. The next size up is a #79 drill which is .0145" or .3683 mm or equivalent to a #37 pilot jet. That might be a small enough step to work. The main is a #135 or 1.35mm which is equal to a #55 drill. The next size up would be a #56 drill which is 1.367mm or a #137 jet.


The main jets is not the problem,the pilot is not available!..what do you think off the size off the main jet? I have fond a nice filter from DNA P-Y2E06-01 and TC-Y2E06-S2 you don`t have to cut into the box,already done!(i get the mine soon :-) )

Shot at 2009-07-24
The main jet a order from Allen's Performance in the UK that folks tell me, that it most be Keihin..and he said,there is not a pilot jet :-(
I wanna buy a set to make self the jet bigger..
Greets Mike(Bike)
(Removed commercial links per policy. -Admin)

O sorry,i did not now,sorry for my bad Englishe to

Aprillia SR 150
Yamaha Tricker XG 250

HorseRider650
Ohio

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USA
589 Posts

Posted on 07/24/2009 at 10:03:02 AM  Member Profile  Reply with Quote
That's an incredible bike you have Mikebike.
As for the jets. If the carb is a keihin you should be able to find a pilot jet. The problem with the XT250 sold in the America is that the carb is a Teikei and no jets can be found.
The air filter cover looks like it would fit both the XT and the XG.
Thanks....

08 XR650L - Sold

mikebike
Deventer

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Netherlands
4 Posts

Posted on 07/24/2009 at 10:27:05 AM  Member Profile  Reply with Quote
Hello fooks...i have the same problem as you guy`s..i have also that fu..ng Teikei Carb...I can`t find jets over here,and i think that i most buy a Keihin FC33..(if it fit??)
Greets MikeBike

Edit..i ment that we most have Keihin main jet into or bike`s..into the Teikei,and not Mikuni!!

Aprillia SR 150
Yamaha Tricker XG 250

robertbenita
California

robertbenita has no Avatar

USA
8 Posts

Posted on 10/17/2010 at 1:42:11 PM  Member Profile  Reply with Quote
Just thought I would mention that I performed the Carb mixture screw (Plug) mod and found it set at (2) turns. I adjusted it to 2 1/2 turns. I uncorked my exhaust with no issues. Cleaned everything up and tools away in about an hour. First thing I noticed was slightly increased exhaust noise, but not excessive and kinda deep sounding. Took it out for a test ride and I cannot believe the responsiveness from the throttle through the gears. As I rode I noted that as the wind noise increased, I could not notice the increased exhaust noise. I went with a 1 1/8 inch hole for the uncork, as I had a hole saw that size. I am very pleased with the results and my concern about exhaust noise levels were unwarranted. This is a great forum and my thanks to those that provided me the information to make an informed decision. And of course, special thanks to lil_mynx for the outstanding mod instructions.

I did think of one more question though...Will this impact fuel mileage and if so how? Thanks again!

2009 XT250
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