darn jetting

[emoguitar131]

Okay guys, before I ask a jetting question, I just want you all to know that I've read all the articles/searches/links about jetting and think I have somewhat of a grip on the subject, but I just want to make sure I'm right before I go making changes. :cool:

Anyway, I have a 93 KX 250 with about 10 hours on a new top end that has run pretty good since I got it last year. The needle clip is in the top position, pilot is 50 (stock) and the main is a 165 (one bigger than stock). I use the stock slide and a plug one step hotter (8). I just cleaned the carb and installed a moose reed cage spacer. Well, I started it up today (using about 3-week old 36:1 93-oct gas) and it was smoking a good amount. I rode it down the street with the choke off and about 6 seconds into the ride, it started to backfire and lose power. I think if I would have kept the RPM's up it wouldn't have fouled, but alas, there I was on the side of the road. Pulled the plug, yep, fouled sure enough.

So I'm trying to get this jetting thing down and it looks like I'm running rich somewhere, right? Could the main one step larger be causing this condition? Also, I thought backfiring was a lean condition? I'm a little stumped because it has never fouled a plug before. Any suggestions?

 

[emoguitar131]

bump... anybody wanna help me out?

 

[kshackleton]

bump... anybody wanna help me out?

I would suspect too rich if the plug is fouled and there is lots of smoke. Try dropping the main to one size smaller than stock and seeing what happens.

Take note of how it runs at each throttle setting....that will give you your indication of what needs to be changed.

I seem to have the best luck by changing only one thing at a time.

Ken

 

[john stu]

do a full throttle run throught the gears (wide open) and then hit the kill swith and pull in the clutch and pull the plug ....what color is it? if its black its rich if its white its lean or the plug is to hot....... if its tan (means good jetting on the main jet) i would start leaning out the other circuits...like pilot, needle

 

[kshackleton]

do a full throttle run throught the gears (wide open) and then hit the kill swith and pull in the clutch and pull the plug ....what color is it? if its black its rich if its white its lean or the plug is to hot....... if its tan (means good jetting on the main jet) i would start leaning out the other circuits...like pilot, needle

This is a good idea....be sure to warm the bike up fully, THEN change to a brand new plug before performing the wide-open throttle run. Once you have the main jet dialed in, you can use this same process to verify mid-range and pilot jetting.

 

[CBRob]

Was it running good before the reed cage and carb cleaning? maybe check for a leak at the carb boot and recheck your reed installation