XT600 98 loosing power over 100km/h
 

This question might have been ask before!

XT600-e 1998 59 000K
Had if for 7 months and great bike I love it
So far I change the spark plug 7000k ago did oil service twice and last one was 1000k ago and air filter was 7000k ago.. I just removed it because I'm getting a new one next week and notice there was oil on/in it and also in the air filter chamber... can it be a real problem or it can be expected from a old XT with 59K
Now the problem is :
When going faster then 100km/h at around 110-120 the bike starts loosing power and kind of chocking on itself like if there was not enough fuel.. if I squeeze the accelerater completely it will keep doing this and slow down to anything between 80-100, if I just let the accelerater go back just a bit it goes back to normal and I can keep riding at 100-105 quite fine but if I snap it all the way the problem persists.

I have no problem from 0 to 100 and the acceleration is quite good but over 100 I just don't get it.. I'm struggling to pass a car or going up big hills at high speed on the highway.

I am learning about bikes everyday so please be patient with me hehe.

I hope I was clear enough in my description..
Cheers!

welcome onboard, add pics...

oily filter chamber is normal, flooded with oil, not so good :)

pull out your spark plug and check the color, if very white-ish, then you are suffering a lean condition, i.e. not enough fuel.
most provable cause would be dirty/clogged jets in the carb, or sometimes even water in the bowl.
easy to check, start with the simple stuff, see if it helps.

One thing many people don't think about when jetting a bike is how airflow is effected at speed . There are some bikes that'll run great to redline in lower gears but at higher speeds they act lean or rich .Any mods done to the airbox can greatly effect this . I see it when running one of my wideband a/f meters . Completely stock setups aren't usually too bad other than a few when certain headwinds or crosswinds .

I'd try going up one size on the main and if it helps , go up another all the while seeing how it's running at slower speeds but higher revs . There is also possible that the slide spring is getting weak and the slide starts sputtering badly at speed as well. If a person puts a camera in the intake tract for veiwing as your riding and most people would be shocked at how badly those cv slide can flutter , no wonder they run horrible .

Check the floatheight, it the fuellevel is too low, the bike will starve for gas at higher speeds. Had this exact problem on a friends xt550. Also check the filter under the floatvalve.

I wouldnt mess with jetting, all my tests have shown that theese bikes are slightly too rich at the mainjets, even with a higher flowing exhaust and modified air intake/filters. This is backup up by dyno runs and my of test with air/fuel tests with a lambda prope in the header on my exhaust. I've never experienced the stuff JJ writes,but have heard about it with pod filters mounted directly on the carb. So I guess theres a lot of variantions to consider.

Oil in the airbox is often becasue the bike is overfilled with oil.

I can highly recommend this supercheap carb rebuild kit: https://www.ebay.com/itm/Yamaha-Carb...from=R40&rt=nc

Hello, 130/110/50 will be better than the original 130/120/46?

check secondary carburetor membrane and fuel filter