Jetting The Carb

[md1985250r]

i am trying to get my 250r to run smooth on the low end ...i do alot of trail riding and it seems the only time it runs smooth is when i get the r's up......can anyone help me?......how can i tell what size jet is in it?...what size jet do i need to run smoother at low rpm's??

[atc86r]

pull the plug out and let us know what it looks like. while your doing that put in a new plug and run it for awhile then remove that plug and let us know what it looks like. a compression test would help.

[md1985250r]

plug is black..kinda shiney...after 1 tank...i have been trying to lean it out a bit ....a little at a time.....

[J.D.]

Well part of the problem is 2-strokes don't generally like trail riding in low RPM's. 2-strokes are high rpm engines, and they're meant to be run like that....if you want to putt around in the woods, get a 250sx or something.

[md1985250r]

hows about you buy me one?? 8) 8)

[KASEY]

a properly jetted 250r will not foul plugs even at putt around trail speed... it takes alot of expierence to keep a two stroke dialed in ,,, i have a 4 year old plug in my 250 and trail ride all the time ,,, here is a jetting chart when you ride try to figure what throttle position needs a change being smooth on the throttle wil help when you figure it out make the nessesary changes and try it again

[skippy]

also you asked what size jet you have... probaly a stocker, just loosen up the big bolt on the bottom of the carb, w the fuel shut off on off, and then grab a small socket, like a 1/4 or around there, and loosen that jet up and pull it out.. you can read a number on it,.. prob anywhere from a 138-160...what mods you got? pipe? filter? porting? bore?

[atc86r]

jet takes 6mm big one on bottom of bowl takes 17mm

[md1985250r]

no mods

[KASEY]

my 86 is all stock it has a 150 main and a 42 pilot jet, thats at 500' above sealevel,,,,

my 85 with a few mods 38 mm carb has a 170 main and a 52 pilot

[TimSr]

Well part of the problem is 2-strokes don't generally like trail riding in low RPM's. 2-strokes are high rpm engines, and they're meant to be run like that....

This is right, but here is what you can do to get around it.

First, dont touch your main jet if your plugs look good under hi rev riding. Drop the needle down to the lowest setting (mode clip up to highest notch). This will lean you out at low to mid throttle, and have no effect on top end. If you try to lean it out with the main jet, you run the risk of a meltdown when or if you do any open riding.

Second get a smaller front sprocket and drop the gearing way down. If you go with an 11T youll be able to putt along at walking speed without slipping the clutch, and youll be cruising slow trail speeds at half throttle or better which will make your two stroke very happy. Two strokes just need to keep the RPMs up, which does NOT translate into riding FAST. Whne you are teaching a child to ride a mini, and can go all day without fouling a plug, you know you are geared low enough! Im geared 11/43 on my TRX250R, and still rarely hit 6th gear on the MX track. I see little value is gearing to do 75MPH on a trail machine, especially when you have to slip the clutch and idle the motor all day.