Jetting/Breaking in a 2 Stroke

pacer · Post by **pacer** » Wed Sep 19, 2007 11:27 am

Just had my KX250 ported. I have it back together, and am ready to break it in. The first run up the block show too lean. As I get ready to fatten it up I am wondering first did I hurt it running it to lean in the first run? Also should I run it a little fat for breakin? Maybe jet it correctly, and just a little extra oil in the gas?

dragracer1951 · Post by **dragracer1951** » Wed Sep 19, 2007 5:19 pm

Jet it correctly and break it in. Please resist the temptation to add "Just a bit" of extra oil. That makes it run lean.
Think about it. A given volume of air. a given ammount of gas and a given ammount of oil. Increase the oil and you effectively reduce the ammount of gas in the air fuel ratio. Now it's leaner.

pacer · Post by **pacer** » Thu Sep 20, 2007 2:10 am

Makes sense. I appreciate the help. It's below 100 here. Time to hit the desert!

:cool

F5 · Post by F5 » Fri Sep 21, 2007 12:48 am

With all slide carbs where the throttle is directly linked to the slide you have to think of Jetting in relation to Throttle position. Not revs. This is where most people fall down.

It is entirely possible to have it too lean in one area & too rich in the other. Yes the mainjet is most important, but an awful lot of 2 strokes seize on closed throttle if the Pilot is too small (more affecting roadrace admittedly).

As always beware of airleaks & airbox/ filter issues.

pacer · Post by **pacer** » Sun Sep 23, 2007 2:59 pm

I am one size smaller on the pilot than stock. That is how I had it before the porting. She would try to foul until warm than was fine. I never worried about off throttle because the bike is set to stall out as soon as it settles into an idle. Am I correct to not worry to much about the pilot?

F5 · Post by F5 » Tue Sep 25, 2007 1:01 am

Pilots are often too rich from std, but whether it stalls when idling is irrelevant. Because you might be doing a bunch of revs on a closed throttle coming into a corner; it won't stall at those revs but it is still running off Pilot.

to requote myself:
"With all slide carbs where the throttle is directly linked to the slide you have to think of Jetting in relation to Throttle position. Not revs. This is where most people fall down. "

see I was right, it is hard to keep that in mind.