Put that lid back on if you havent rejetted yet . The bike is way to lean without the airbox cover on . Once you rejett and make sure the carb is set right go ahead and romove or replace the airbox cover with something appropriate.

Regards,

 

Travis,

I'm not trying to blow you off, but HERE is an excellent article on tuning the Keihin CVK40 carb. Aside from the size, it is the same carb on our bike.

Read through it and you will understand that by taking the airbox cover off, you have allowed more air to feed into the carb. Now a proper air/fuel mix (the job of the carb) is around 14 to 1. If it is leaner, it does not let the engine burn it right and not enough power is produced. It is is richer, then you get some dark smoke (unburned gasoline) out the tailpipe. Either way the bike will not make maximum power.

Anytime that you make a change to the amount of air and fuel that can be fed through a 4 stroke engine - less restriction on the intake side (like in opening up the airbox), less restriction on the exhaust side (like in opening up the muffler) or bigger valves, carb, more cam timing, etc; you will effect the proper air/fuel mixture. This is why you need to change the main jet to one that is "just right".

In the CVK style carb, there is a needle that makes the transition between pilot (idle) jet and main (fast) jet. By shimming the needle, you can keep the fuel curve at a point where you make maximum power.

Got you interested now?

That's why all of us that have put the "Grapevine Texas Mod Package" into our bikes are so impressed!

 

I took off my snorkel. i love the way it sounds and to me it seems to run ok. so are you guys saying that you should not do it untill i can get it jetted.

 

Zubie8,

A lean mixture makes a lot more heat than a fat (or rich) mixture. Pistons can sometimes holes appear in them when the mixture is too lean and the engine run hard for too long!

I have an old outboard with a piston that is melted to the cylinder wall. I was running it wide open and kept leaning out the mixture. It was really buzzin' along when all of a sudden it just stopped - like real quick and real solid! I knew there was a problem when I grabbed the rope and gave it a yank and the motor could not be turned over! It does happen.

Do all of us a favor, especially your KLX250S and put the jets in that we suggest, then open up the airbox!

Just makes sense. Know what I mean, Vern?

 

If you are going to run with the air box cover off your going to need a after market full exaust system, re-jet, and drill crank case vent.

I am running 6 half inch holes above my filter in the cover with the snorkle removed, 128 main jet, e-clip on third groove on the jet needle, drilled #32 slide valve, and 2 and a half turns out on the fuel screw, with the full muzzy system and drilled out crank case vent. My bike runs mean as hell it takes off threwout the power band with enphasis in 1/3rd and rip through 2/3rds to full.

 

thanks marty. I put it back on. I thought that if I was running to lean it would not run so dam good. Do you have a suggestion for the needle and what slot to use. If a took it back off, I also drilled the exhaust. thanks again.




matt
keene NH