New to the forum & I have a carb. question for my 2013 KLR. After I do the .22 cent mod, what size of jet would you recommend for my bike? Everything is stock and it seems to pop quite a bit when decelerating. I am @ 5200 feet elevation wise. I appreciate any help!
First, welcome to the forum!
Slight backfiring during deceleration ain't no thang, IMHO; may be reduced by adjusting the FUEL SCREW. Google, "Care and feeding of the CVK40" for a good primer on the carb operation, and location and access to the fuel screw. About 1.75 turns out from a SOFT bottoming is a good starting point for a stock engine, IMHO, in contrast to what a service manual might say.
The 22-cent mod doesn't affect jetting, IMHO. Rather, raising (shimming) the needle fuel-enriches mid-range operation (might not be particularly effective or necessary at 5200 feet elevation); drilling the slide vacuum port may enhance throttle response.
Otherwise, with a stock engine, and essentially stock carburetor (stock needle, but shimmed one # 4 washer), I think your stock jetting's pretty close to optimum for typical KLR650 service life, although at your elevation, a smaller main jet may fuel-lean your mixture more optimally. Your bike, and YMMV ('Your Mileage May Vary').
No harm in experimenting with jetting; everything can be restored to stock operational condition if you don't like the results. My riding partner has 55,000 miles on his '08; been from Canada to Mexico; restored his carb to stock condition, early on, and left it that way.
Diverse opinions abound on jetting; everyone has one; find what works for YOU.
Full disclosure: Near sea level operation; 22-cent mod (one # 4 washer, 7/64" vacuum port), 1.75 turns out on fuel screw, on my otherwise stock '07. Mileage in the high 40s, mpg-wise; starts, runs fine. "What? ME worry?"