Tune carb for the trail

['01 YZ125]

My son has an 01 YZ125 which is all stock but runs like a scalded ape on the track. Problem is that where we live he mostly rides trails and visits friends in subdivisions. As a result the rpms aren't up there where they should be for a race bike. The result is that the bike bogs down from loading up, quits, and won't restart until the plug gets the oil cleaned off of it. This is a pain in the ass and I am asking whether the fix is simply adjusting the jet needle in one more click or should I look at rejetting? Any help or advice would be greatly appreciated.

Doug in SW Florida

 

[truespode]

You need to look at re-jetting.

First make sure the silencer packing is fresh and then re-jet.

Re-jetting should help on the trail and on the track.

Ivan

 

[2-Strokes 4-ever]

We've always used MX bikes to convert over for off-road/woods riding. Like Ivan stated, re-jetting is most likely the issue. We have found that because of the "lower RPM/riding-in-the-torque-portion" of the powerband needed for woods stuff, that leaning the pilot, and most likely the needle, is necessary. However, be careful with the main jet, especially on a 125. Little 125 motors often times have to work so hard, that you want to play it safe when on the main... (muddy or sandy situations for example.) We always jet to run crisp on bottom and in the middle, and stay slightly fat on top to play it safe. Get it dialed in and you'll be amazed at how much better it will be on the trail.

 

['01 YZ125]

Thank you both for your insight and advice. I used to fly ultralight aircraft powered by Rotax 503 engines with Bing carbs. I got used to tuning them so I guess it won't take too much effort to master a Mikuni carb. I installed an exhaust gas temperature gauge on my aviation two strokes which allowed me to see exactly what was going on inside my engine at different jet and jet needle settings. It made adjusting easy because all you had to do is simply look at the gauge. Does anyone do this on dirt bike engines?

Doug in SW Florida

 

[flynbryan]

A gearing change will also greatly help a 125 in the woods. It will allow you to stay in the upper rpms easier thus keeping you from bogging too much and loading up the motor.

 

[2strokerfun]

We always jet to run crisp on bottom and in the middle, and stay slightly fat on top to play it safe.

Words to live by