06 KX250F running lean

Stroked87lx · Jul 19, 2011

A little background:

I bought a 2006 KX250F a week ago. It ran but would not idle without the choke on and backfired alot while riding down the road(test drive). Guy said it was rebuilt last year, has around 15 hours on it and sat all winter. I ended up getting the bike, 2 rear sprockets, 1 front sprocket, chain, riding boots, triangle stand, under frame stand, extra plastics and helmet for $1000.

Got home, cleaned the carb(main jet had some visible trash in it) sprayed everything with carb cleaner and blew out with air like the manual said. Put it back together and it backfired like crazy and had a bog going down the road.

Changed the plug, and ran it at idle a few blips of the throttle and the plug is white. The bike has the following:
Full Pro Circuit Exhaust
Main Jet: 170
Start Jet: 68
Leak Jet: 55
Slow(Pilot) Jet: 42
NCYU Needle on the third clip

I changed the needle to the 4th clip in hopes of richening the mixture but the plug is still white and backfires still.

The valves are all within tolerance but the right side intake valve is .001 tight. And the timing is correct also per the manual.

I have not set the float height, but would this cause the bike to run that lean?

I'm thinking I need to re jet it. If this is the case, which jet kit would yall recommend? JD Jet kit?

Sorry for the long post. Thanks in advance for any help.

williams805 · Jul 19, 2011

Did you pull the pilot out and look at it? You said the main had debris in it. That what I would check right after I check for a vacuum leak. Spray carb cleaner around the back of the carb and intake. If it revs up while you do this you know there is a leak. If there was shit in the main, it probably in the pilot as well. and the holes are much smaller. If this carb is anything like the Mikunis are, the main has the most affect at WOT. so unless is lean at wide open id be looking elsewhere.

When you pulled it a part did you put everything back with the same settings? Try going fully in (lightly seated) on the mixture screw. Back it out 1/4 turn at a time and see if it is making a positive change. If you go too far and it starts to run poorly again, go back 1/8 or 1/16 turn at a time. With Mikuni's, if your out more than 2-2.5 turns you need to get a bigger pilot.

Call Procircuit and ask them what jets they recommend for your year bike. That’s what I did and their set up ran flawlessly.

Stroked87lx · Jul 20, 2011

Yes I pulled the pilot out. I pulled every jet in the carb and flushed them all out with carb cleaner and air and small drill bits on the ones I had small bits for.

Today, I tightened all the clamps, started the bike and turned the pilot screw out and the idle adjuster out to lower the idle some and the popping went away even when I give it throttle(on the stand).

Then, as I'm messing with the throttle revving it a little, it dies as if I hit the kill switch. Kicked it a few times but it wouldnt start and I had to leave for work so I just left it alone.

But I did pull the plug and it is still a little whitish, and this is on the stand revving it, not riding it. So I can only assume it'll be worse on a ride. And I dont want to run lean for too long and pop a piston.

Think I should try a 175 Main?

Stroked87lx · Jul 20, 2011

Not popping or backfiring anymore. The only thing i changed was the pilot screw and idle so maybe I didn't have it out far enough. And I rechecked the clamps on the carb inlets and put a little more muscle on them so maybe there was an air leak.

Now, the bike runs fine. Ran it down the road, no hesitation, no backfires.

Turn around, and it dies. Takes a few kicks but get it going again, go about 200 yards and it dies again after I pull in the clutch. Pop the clutch to try to get it going, motor turns over but wont start. Kicked it and no go. Had to push it back to the house.

The plug is now black, not whitish like before. Maybe I need to put the needle back on the 3rd clip? But why did it turn off all of a sudden?

williams805 · Jul 20, 2011

Too rich now. Clean plug. Go back on the mixture screw in small increments.

I still recommend you call procircuit to see if you have the recommended pilot and main jets. They will also tell you the recommended needle position. On my 04 RMZ250 w/full Ti procircuit i think they recommended one up on the pilot size and raising the needle one position. This may have already been done on your bike that’s why you should call to confirm.

Stroked87lx · Jul 21, 2011

I found the settings online.

Pro Circuit MAIN-170 PILOT-42 NEEDLE- NCYS CLIP SETTING- 3 PILOT SCREW TURNS-3 LEAK-50

But, I have a 55 leak and a NCYU needle.

And, my pilot screw turns by itself while the bike runs. I've read there is supposed to be a spring, washer and o-ring in the hole but the only thing I have is a spring?

williams805 · Jul 21, 2011

Stroked87lx said:
I found the settings online.

Pro Circuit MAIN-170 PILOT-42 NEEDLE- NCYS CLIP SETTING- 3 PILOT SCREW TURNS-3 LEAK-50

But, I have a 55 leak and a NCYU needle.

And, my pilot screw turns by itself while the bike runs. I've read there is supposed to be a spring, washer and o-ring in the hole but the only thing I have is a spring?

The o-ring may keep the screw from turning. You'll never get it to run right if it turns on its own.

I would go with their suggestions on the needle and leak. The 3 turns is probably +or- 1/2 turn (ish). Keep in mind your altitude will affect these settings. If you're in Denver you may need to play with it a little more.

Sounds like you know what to do. Let us know how it turns out. Sounds like a good deal on the bike.

06 KX250F running lean

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