Modern Buddy

Hey all,

Been awhile since my last post but I'm looking for some info. Checked the Tech section and didn't see what i needed so here it goes.

I recently move from Arizona Which is low elevation to Montana where I'm living around 6-8k feet elevation. My scooter runs fine for the most part, however at WOT it seems to stall out for just a half second, and the bike jerks a bit, as if it is getting to much air or to much fuel. I'm not sure which one. I would think it is the fuel as the air is thinner at higher elevations? Was wondering if this is a easy fix that i can do myself, and if anyone could point me in the right direction.

Thanks again.

With the higher elevation, your engine is running rich at WOT. Drop the main jet size down one step at a time checking the sparkplug color (should be a tan color) and the engine runs smoothly at WOT. Double check, but I think the stock main jet in a 125 is a #102.

Im not 100% how to make sense of that. Should I start with a new Spark Plug, my current one is about 2000miles old.

Moejazz wrote:Im not 100% how to make sense of that. Should I start with a new Spark Plug, my current one is about 2000miles old.

Couldn't hurt to change the plug. If you've never tuned a carbureted engine before, I'd suggest getting some help because it involves draining the carb of gas, removing it, removing the bottom carb cover, swapping main jet, reassembling, making a few full throttle passes, then pulling the sparkplug to take a reading (check for the correct color). You will have to do this several times until you get it right.

change the main jet FIRST

your spark plug is a good indicator of how you're running, no need to change it as it's probably nice and white at your altitude.

I wouldn't think you would have to go through that much trial and error. Is there a Genuine Dealer near you. Check with them and start there. If not, call Sportique scooters in Denver. Ask what they are running for jets. Not quite as high as you, 5300 ft, but higher than Arizona.