What would be the best all around main jet size for my stock KLX250sin the Colorado moutains? I know the stock 118 MJ runs the bike lean at sea level so I wonder how it would run in the mountains? If I found it running lean with the stock MJ I could take off the lid which should run it even leaner right?

 

Are you only planning on changing the main jet? No other mods?

I ride between 5300 and 11,000 feet. I use a KDX snorkle, a 122 main, stock pilot, and Big Gun exhaust. The main jet you choose will depend on how much air you let in, and how much you let out...

 

I have no mods sostock should be about right in the mountains, right?

 

I doubt it will run satisfactorily in the mountains in stock form.

Mine wouldn't go above 8000ft. It wouldn't die, but I had absolutely no power. I've heard that others have had some success removing the airbox lid to keep going at altitude (the air is less dense the higher you go), but I never tried it. It's really easy to wake up the motor, and you really don't have to spend a fortune. If you want to quietly go up and down the mountains, find yourself a stock KLX300R headpipe and muffler on Ebay. That, coupled with the "free" mods, a 120 or 122 main jet, shim or replace your needle, and a KDX snorkle (or pull the snorkle), should be all you need.

Your tiny plugged up exhaust, and catalytic converter have got to go! Your snorkle has such a tiny inlet area that it's a wonder the motor will run at all. Let more air in, adjust the mixture screw to match with a slightly larger jet and adjustable needle, let more air out. It's more than worth the effort if you're going up into the mountains. All the instructions (with pictures) are available on this forum. It's really easy to do.

Good Luck.

 

I live in Utah at about 4500 ft. Three weeks ago, spent the weekend between 9000 & 10,000 ft. At 40 mph in 5th gear the bike would bog if I gave it too much throttle, and it was difficult to get over 50 mph. During the next week I ordered a K&N air filter and the high flow snorkel, but they didn't get here in time fornext weekend, so I just cleaned the air filter and hoped for the best. I think I reoiled the stock filter properly, but did my best to wring out any extra oil. Last weekend the bike ran much better at 9000 ft. Didn't get a chance to go higher.

The K&N filter and larger snorkel came in on Monday. On the 4th, I pulled the spark plug before doing anything else and found it to be black and sooty. Not real bad, but definitely too rich, so on went the K&N and the larger snorkel. The bike sounds better. Don't know why but the exhaust noise seems about and octave lower than before. The bike runs better at home (4500 ft). It'll do 80 mph (according to the bikes speedo, everything else stock) on level ground in still air. That's as fast as trafficwould allow, but was pretty much wide open. It doesn't feel too lean, but I plan on pulling the spark plug on Saturday just to be sure. Don't know when I'll get back to higher altitude.

 

I too am trying to figure out the jetting for 4,500 ft (Alamogordo, NM). Everything is stock now but my KDX snorkel, K&N air filter, and hmf slip-on will be in next week. I ride up to about 8,000 ft and the bike could use a wake-up call. Based on the advice of others, I'm going to start with 122 main and stock pilot. I noticed most people on the forum jump from 122 to 125, but there are also 123 and 124 sizes. Is there much of a difference when you only go up one size? I really don't want to take the carb apart more than twice [sm=insomnia.gif]

 

I live at 7500 ft. and ride to 11,000+andhad my KLX running good with: dual snorkel, Uni filter, slide drilled to 7/64, 118 main and 35 pilot jets,N1TC needle on secondslot,air/fuel screw at 1.75 turns out, KLX300 exhaust (nice and quiet),and all the smog stuff removedwith gearing at 14-48. A good skid plate (Utah Sport Cycles), bark busters, and some better handlebars would be a good idea if you plan on anything other than forest service roads.

 

I want to try just changing the main jet and keeping the stock needle. Do I need to remove the carb to do this?

 

The needle has more effect on overall jetting than the main.

 

Is there a "how to" on jetting the carb w/pictures anywhere?