Klx250s melted piston help?

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#121

05-10-2013 | 10:40 AM

Richard Avatar

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Joined: Mar 2013

Posts: 866

From: SE Asia

Quote:

Originally Posted by Ranger Ron;460215 [I

Usually with a big bore, you don't have to make much of a change with the main jet. The reason for this is that with a larger displacement more air is being drawn into the engine for the same piston speed. This increases the intake velocity. The increased intake velocity adds more fuel automatically.

If I remember correctly, the oem main jet for my 2006 was a 118. With the 351 a 120 main works best for me. [/I]

Ron

This thread is a couple years old, but I am just getting into KLX250 mods and find it interesting you are/were running a leaner main jet than the 300 comes with on the much larger 351. You attribute that to you using the 300 emulsion tube, yet of course the 300 engine with its OE (factory lean?) 128 main jet uses the same emulsion tube.

You've probably did other mods as well which would have normally required richer jetting, making the 351 w/ 120 main even more surprising.

I have found that if one is able to increase vacuum draw across the jet orifices in the carb floor thru one mod or the other, it is possible to find your jetting is now too rich. I have had to back off a size on pilot jets because of it in the past on other m/c engines.

So maybe your other mods: intake and exhaust were just the right combination and were getting the fill benefit of the 120 main