I recently rejetted, and loved the performance increase. I rode maybe 125 miles at Ocotillo Wells, altitude about 1,000'. My mpg isn't very good though and I suspect it's running too rich. Since then, I rode Big Bear twice, altitude between 6000-8000' and suffered so bad, I can't return with the jetting as-is.

2014 KLX250
stock: 35/118
6 Sigma: 38/125

In stock form, I rode everywhere no problem. Shall I go back to stock jetting and forego the performance increase for ridability?

 

Please list all performance mods and all carb setups you've used.

 

• Stock air cleaner, no airbox mods
• GPR slipon exhaust, stock header
• stock carb, now jetted 38/125, drilled slide/stock needle
• smog removed
• Clarke tank

 

I should mention, on the street/freeway here at home (Mission Viejo, CA altitude about 600'), the thing runs fantastic, any throttle position, pulls hard all the way to indicated speed of 75mph. Sprockets are 14/50

 

Stock jetting is indicated for your mods - especially with a drilled slide.
Stock pilot jet is indicated for your mods - that #38, when set properly for sea level, will start becoming rich as you approach 5000 ft.
Lean the main jet in small increments until the bike runs acceptably ( to you ) at 8000 ft. That jet size will be your best compromise.
Set the fuel screw toward lean from the point that is halfway between idle drops.

 

Thank you @Klxster , very much appreciate your advice!

 

Sigma Jets just replied, saying the same, stock jetting is needed at altitude. As it works at both sea level and mountains, best to keep what Kawasaki gave me. So much for my performance increase, short-lived!
As I ride both sea and mountains fairly often, I can't swap jets that often so I'll sacrifice the sea level increase for the overall dependability. The was a $40 purchase (Sigma Jet jet kits) for nothing.

 

All owners should ask first, in here, before modding the CVK.

@LaGrasta , you need to restore your slide lift port to stock size ( or even a bit smaller than stock ) - see post #8 on my "CVK34.." link below, for the particulars.
Oversized lift ports and cut slide springs ( or the weaker DJ spring) are all items that weaken, or even defeat (when used in combo), the CVK's ability to "self adjust" fueling for altitude changes.

If you have a stock lift spring ( replace it if in doubt) and after restoring the lift port, you have multiple options to try - in order to find a better compromise of power at sea level with operability at 8k alts.

For instance: If your spring and port are non-stock, and you restore them to stock, your current jetting will operate much better at 8k ft. than it does now.

Regardless, you need to find the point halfway between idle drops, then turn the fuel screw in until just before lean idle drop. Or replace the 38 back to the stock 35 and use the standard 2.5 turns out. Either way, once done, the pilot system will be better set for 8k operability ( this means idle quality and response to throttle changes.)

 

Also, for all owners of CVK carbs:
There has been so many decades of "hair brain" mods, pushed out in forums, that such idiotic nonsense has/had become "normalized".
Even the DJ kits use mods that compromise the CVK's ability to compensate for altitude.
Point being, if you bought your bike used, it likely has had some mods to its' CVK ( from previous owners) that could/may cause problems at high altitudes.

 

Thx Klxster. My spring is still stock, but I did drill the slide out.