High Altitude carb setting questions for stock bike
 

Hello Folks,

New to this forum, but for the KLX 250S this seems to be a great place to gain some knowledge. I have a new to me 2007 KLX250S that is basically brand new and bone stock with less than a 100 miles. I have ridden the bike in the past (before buying it), but it ran very poorly. I suspected this is do to a gunked up carb, so the first thing I did was remove the carb last night(a major PITA!) and am in the process and giving it a serious cleaning as there was plenty of varnish. I plan on doing the #77 drill bit mod to the starter jet, but while I have the carb out I have some questions about what else I should consider modding.

I live at 5000 ft, and most of my riding will be above 2500 ft to 10000 ft. I know the stock jets are lean for sea level, but after hours of searching I have no definitive idea if the stock jets are good for my altitude. At this time I have no plans to mod the exhaust--just gonna leave it stock for a while.

Second, given the altitude and stock configuration is drilling the slide a good/bad idea? What about the 22 cent washer under the needle?

The shop that sold the bike must have set the fuel (pilot) screw because it had already been drilled out. I have read tons of stuff about the Kouba screw, but for my altitude what is a good start point for the stock (currently at 2.5 turns out from light bottom).

Finally, the sanity check. I am having a brain fart and can't recall the order of install on the needle and white needle keeper. The diagrams show the needle going in first, with the keeper on top and then spring. Is this the correct order? Something in my brain has the needle on top of the keeper.

Thanks for the input and suggestions.

My buddy took his stock jetted bike all the way up to 12-13K feet KLR650. No problems.
Attachment 11725

I live at an altitude of 3,500 ft and take my bike up to 8,000 ft all the time and can tell little difference. If you were to stay at a set altitude, it might be worth rejetting for that level. I go between 0 and 8,000 several times during the year and I am with you, that carb is a pain to get out. I have also had to use SeaFoam in my fuel due to the varnish build-up in the carb, mainly in the idle ports.

If you're planning a trip where you will be well above 5k for a while, I could see dropping one main jet size and MAYBE doing one notch (or a half notch) on the needle. But given the lean nature of the bike at sea level, where you are now, it's probably fine.

If you google around, you can find a carb jetting calculator. It lets you plug in your current elevation and carb mods and gives you a chart of what to use at other given elevations. From my own experimentation with this, there's rarely more than one main jet size difference.

Another option instead of having to open the carb is to just plan on pulling your airbox lid off when you get above, say, 7000-8000' and see how that does. Or just pull the snorkel out. I wouldn't do anything permanent like drilling holes unless you have a way to plug them again later.

Rob

I live at 4,700 feet, and ride up to 11,000+. I have never had to fiddle with the jetting for altitude changes, and it seems to run fine for me.

I *HAVE* re-jetted mine for my aftermarket pipe though, so it's not "exactly" stock jetting. You can't do harm riding up high with stock jetting. At the very worst, you'll just be running rich.

Bikepharmer, your description of the order is correct.

On the jetting, I think your stock setup should be fine. With the stock setup being somewhat lean already, I don't think you'll have an issue with the rest of the intake and exhaust also being stock. I think your gearing numbers will probably be more important.

i've put it out there once and i'll do it again build a little a/f raito meter that you can pull off and put on its pretty easy a wideband o2 and a guage it will make jetting and tuning a no brainer

I still have not seen a lean afr on a stock bike, the jetting is not bad, the stock exhaust is a major bottle neck.

Great, and a big thanks!
 

I have it back together and it fired right up! I am still in "break in" phase limited to 4000 RPM. I have been taking little strolls down back roads just enjoying how light the bike is, and sleepy the little motor is. My other bike is a KTM 990 Adv, so it is a pretty big difference. I have no plans to do any mods until I get past the full break (1000 mi), and then re-assess what mods to do. Exhaust and 13t counter sprocket seem like a no brainer.

Bike seems to run fine with 2 turns out on carb fuel screw, everything else bone stock as it left the KHI factory in Thailand. I did add a little tail bag ;). I have also added a little fuel condition/cleaner to the tank, and will do so for the first few tanks.

Speaking of that, first tank calculated out to 76.6 miles/gallon. I like that!:D

Need link!
 

How do you make one of these?