FACT OF LIFE:
Seems as I go higher up the bike performs with less power.
Question, should I go larger or smaller on the main jet, or leave it as is. It rides great on the highway and around town, but if I go up in elevation (example: mountain roads or trails) it starts to bog a little, especially going up a steep hill.
Any and all naturally-aspirated (as in, no turbocharger/supercharger) internal combustion engines LOSE POWER at altitude. The big boys on the playground say, at the rate of 3 per cent per thousand feet. Why? Less oxygen to process fuel, less fuel processed per unit time; thus, less power.
The stock Kawasaki/Keihin CVK34 main jet for a non-California USA KLR250 is 120 (trick jet kits may have different numbering systems). You might dare a 118, but . . . even with perfectly optimum air/fuel ratio, you will lose power at altitude.
If the bike starts easily, accelerates smoothly . . . being a little fuel-rich is better than being a little fuel-lean. Your bike, your call! My approach (unless I move to Denver): Just wind it to redline!
Oh, yes; on OVERHEATING the KLR250: BURPING
remains critical to the KLR250 cooling system. To burp, operate the engine with the radiator cap OFF, 'til the coolant circulates freely (expelling trapped air). Shut down, top off radiator with coolant, fill overflow reservoir to FULL mark, restore radiator cap and ride on.