Hey guys,

Just picked up a KLX 250 and have the 300 kit bolted up so I'm all ears on tuning. You've got some great topics I've been reading through and lots of good info.

Here's some food for thought. O2 sensors come in two types, wide band and narrow band. The types you see in Jegs and Summit are Narrow band sensors and don't have the capabilities for precise tuning due to their narrow range. They can tell you if you are obscenely rich or lean but when fine tuning they lack the scale to measure correctly. Most of us can tell when we are grossly lean or rich, it's the fine tuning that gives us all grey hairs[:@]. Proper Wide band o2 sensors are what you need for precise tuning and run around $300-400 if I remember correctly.

If we all chip in $20 or something we could buy a quality wide band sensor, give it to Nobrakes to get his knuckles busted swapping jets 'n stuff and then he can post his findings. I'd pay $20 to have someone do the grunt work.

 

I'd pitch in for that, but I doubt we could convince Brian to (a) swap out his current O2 sensor that is welded onto his headpipe or (b) pull that fancy-schmancy pumper carb off to waste time tuning a lowly CVK carb. [:'(]

If those two hurdles can be cleared, then just tell me where to send my $20.

 

Well, if a wide band sensor costs $300 or $400, I can tell you I definitely don't have one. Mine cost $60 and was described as a "Universal" sensor by the guy at Autozone. And while it may not be optimal, it has served its purpose. The voltage output may be a bit sensitive in the stoichiometric range which, but it there is some measurable change as the readings go rich. The reference I was using on this was a tuning guide for the FCR carb that I have and it was saying just get a cheap O2 sensor - didn't have to be anything fancy. But you do need a good voltmeter. I happen to be using a microcontroller with a 10-bit A/D converter which can sense down to 2.5 mV (0.0025 Volts). Where I want to be with this sensor is around 0.7 to 0.9 volts. 0.5 volts is stoichiometric - all O2 burned, all fuel burned. But for best power, you want to be a little bit rich.

I'm sure a wide-band sensor would be better, but for my purposes the sensor I have is working OK.

And regarding the CVK, it performed really very well when I used it on my 331cc and I was especially happy with its mid-range power. The key is to get it jetted correctly, of course. But it won't provide that snap that a directly controlled slide -type carb will and especially one with an accelerator pump to give that squirt of fuel when you open the throttle to compensate for the lean condition that occurs at that time.

I can remove my sensor very easily, though. It just unscrews and I have a plug to screw in place of it. I think it is a standard fitting so changing out to another sensor would be easy. I'd probably just need to change a few firmware parameters and recompile.