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Old 12-23-2012, 10:36 AM   #1
prichmon OP
Gnarly Adventurer
Joined: Feb 2009
Location: Huntington, wv
Oddometer: 138
KLX250SF Carb starting and cold run issues

I have done significant research but can't get the bike to start and run right cold.

From a cold sit:
pull choke
turn on gas
hit starter for 5-6 seconds - no running
wait 30-60 sec
hit the starter for 3-5 sec - may run or may not
wait 30-60 sec
hit the starter for <3 sec - usually runs
Idles for 1-2 minutes as it heats up then dies
crack throttle and crank -- bike restarts but must hold throttle open with choke off to make it run
After 3-5 minutes it will maintain a low idle without throttle.

Once warmed bike runs GREAT.

I have owned a dozen+ motorcycles and have NEVER had this much trouble making them run right. Cold or HOT!

I have rejetted to a 124 dynojet main, KLX300 adjustable needle on the 3rd position, changed the idle to a 38 with 1.5 turns out. Lastly I drilled the choke orifice to ~19-21 thousands. No Toil Air filter, air box top off or on has had little to no effect on running. Exhaust has been drilled with a 1/2" through the baffle and end is drilled with 6 1/4" holes in the end cap.

The only thing I can come up with is a lack of "1/2 choke" which allows mild enrichment. The sf has a carb which the choke is on or off only.

If anyone can lend a hand I would appreciate it.

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Old 01-09-2013, 11:32 AM   #2
Noobie McNoobington
RockabillySlapMatt's Avatar
Joined: Jan 2013
Location: Las Vegas
Oddometer: 209
What temperatures are you starting in? I did the 124 main and dynojet kit, but left the stock pilot in with 3 turns out. At 30 degrees F it takes a choke still(I keep it garaged).
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Old 01-09-2013, 12:00 PM   #3
Joined: Sep 2012
Location: Robertsdale, AL
Oddometer: 99
Drain the float, turn gas on, wait 10 sec, choke, then start.

Next time, turn your gas off a block away from getting home, let most of the gas or all of it run out before turning it off. That should clear the issues, does for most.
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Old 01-09-2013, 05:40 PM   #4
Candyass Camper
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Joined: Mar 2007
Location: Tejas
Oddometer: 4,629
Drilling out the starter jet to .018" will aid cold starting in almost all cases. The stock starter jet is too small for cold weather for many owners. The jet is pressed in so you can't replace it. You drill it.
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Old 01-09-2013, 06:42 PM   #5
maxjett's Avatar
Joined: Aug 2007
Location: Raleigh, NC
Oddometer: 708
I did this primer and works great, found one in Ebay.
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Old 01-11-2013, 03:26 PM   #6
prichmon OP
Gnarly Adventurer
Joined: Feb 2009
Location: Huntington, wv
Oddometer: 138

Temps are no lower than 40*F or so. I have already drilled out the starter.

Short of draining the bowl I have covered all of the recommended suggestions. I shut the fuel off ~1/4 mile from my stop if it will sit for a long while.

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Old 01-11-2013, 03:39 PM   #7
Nobody's Robot
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Joined: Aug 2010
Location: Southern Maine
Oddometer: 2,911
Have you checked your valves recently? Many KLX owners leave the pilot jet stock when rejetting, the 38 pilot may be too big? How did you arrive at the 1.5 turns on the idle mixture screw? You really need to adjust that with the bike running and warmed up. Screw it in until the engine starts to stumble and then back out 1/4 to 1/2 turn. Blip the throttle and watch/listen for the engine speed to drop right back down to idle. If it hangs at a higher RPM, turn the screw out a bit and retest. If the engine speed drops down below normal idle speed, turn the screw in a bit.
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