Hello from Montana. I've got a 2006 KLX250S. It has the common cold hard starting problem that I manage by getting fresh gas into the float bowl. But it also has a more perplexing problem, hot re-starting. After full warmed up, if I stall or shut off the bike, it usually refuses to re-start with the E-button. I have tried no throttle, 1/4 throttle, full throttle. Everything I can come up with. I know the gas is fresh in the float bowl because it was just shutoff. But what makes it even more baffling is that if I put the bike in 3rd or 4th gear, I can bump start it with typically one compression stroke. If I'm on a hill, this usually is not a problem, even on flat terrain by running alongside, hopping on and dumping the clutch, the bike usually roars to life. I've verified that I'm getting spark with a timing light while using the e-button. I've got a brand new battery and it will crank for minutes, but the bike will not come to life. I'm thinking that it is more than the presence of spark, but more about quality of spark? Maybe a bad coil? Or do the headlight/taillights which come on with the key, reduce juice to the ignition enough to make it difficult to re-start when hot? Any thoughts or advice would be appreciated.

 

have you tried with choke, is it possible it's too lean and doesn't want to fire even warmed up? When you rev the motor when it's idling, does it drop down to a steady idle.. or drop down a little, then drop down more after a few seconds... or drop down far and then come back up after a few seconds? either of these is lean or rich respectively... something to think about in addition to spark issues.

 

That can be tough one to diagnose. Is that your original battery in your '06? Even if it is, if it spins the starter strongly, that's probably not the issue.

On the headlight, I have mine switched on my '06 just in case I get marginal battery power somewhere in the boonies. It's a 60 watt issue, not the end of the world, but might make a difference in a tight spot.

The ignition is usually a non-issue on these bikes, but it's not beyond possibility. The fact that yours is working, but might be working at a reduced output makes diagnosis a pain. Still, I think this is unlikely. For grins, insure that your plug cap is thoroughly screwed into the plug wire and there are no obviously loose connections at the coil, wire, and cap. Pull the plug so the motor will spin more freely. Have the plug attached to the cap and ground the plug against the head with an insulated handle screwdriver, a piece of wood, or other object that won't allow you to get zapped. Spin the motor with the starter and see if the spark is a strong, blue-to-white color. If it's yellow-to-red, look further into your ignition or connections.

I'm going to take a stab at the solution being fuel/carburetor related. I think your bike may be starting when you bump start it because of fuel delivery. If the fuel level in your carb is low it can affect both cold and hot starting. Bump starting kind of masks a low fuel level because enough fuel sloshes into the pilot circuit to help starting. Fuel level should be set by checking with a clear piece of chainsaw fuel line...or clear battery vent tube...against the side of the carb body...just like the factory service manual shows, except without the costly special tool. Just checking the static float height by a fixed measurement isn't positive. You can do this without removing the carb. Just have the bike level, attach the clear plastic line, hold the line looped down and up against the carb body at the line where the float bowl and carb body meet, then crack open the float bowl drain screw. The fuel will flow in the plastic line to the "real" level that the fuel is inside the carb. If it's + or - 1mm of that junction of the float bowl and carb body, you're good. If not, pull the carb and make adjustment to the float tang accordingly.

If you have to pull your carb during any of this, drill out the starter jet with a .020" drill bit. This will stop the cold starting issue...if your fuel level is correct, of course. The starter jet is next to the main jet. This alleviates that need to putz with your float bowl draining routine.

 

Thanks for the excellent input. I besides trying different throttle positions on hot restarts I have tried the choke. No help. Once running the bike settles into a perfect idle, never flutters up or down. I think the pilot/idle circuits are pretty much spot on. The float bowl angle is very interesting. Next time I have the hot re-start problem, I'm going to try shaking the bike side to side to slosh some gas around and see if some works it into the pilot circuit. I will post my results soon.
Thanks again.

 

I took if for a ride. Good and warm. Shut if off. Tried starting it while shaking it side to side. No luck. Fortunately I stopped on a downhill stretch. Bump started it, first compression stroke. Repeated the process several times. Failed each time.

I still will check the float level. I assume that I attach the clear tube to the float bowl drain port that currently has a black tube attached to it. Correct?

Also, I would like to hear where is the best point to install a light cutoff switch.

Thanks for all the help.

 

Yeah, the bowl drain is at the bottom at the black hose. I installed a simple push/pull switch behind the number plate that only involves the ground wire to the headlight. You could get fancy and get into the wiring some more to kill the taillight too, but I didn't think it was worth it. I have a Vapor instrument panel, so there was perfect place in the hardware already on the bike to mount that switch, but these kinds of switches aren't hard to mount just about anywhere.

 

Are you sure your pilot jet is the right size and not too lean? Coz I had a very similar issue when using the stock pilot jet, but when I went to a #38 is solved the problem.

 

Float is a good thought as described above.. but I prefer adjusting this off the bike. I'd rather pull the carb and do the slow tip upside down method to just see it for what it is rather than trying to pull the bowl off to make adjustments upside down, which I dont think you could even do on this bike even if the clear tube gave you a reading.

Are all your vacuum lines/holes either intact or properly sealed off too?

And just to clarify, when TNC says to drill out the starter jet, he means just to pull of the cap that covers the screw... you can see it in the mod day thread.

Let us know how the spark situation looks and such.

 

If the bike starts easy when bump started but not when cranked, I don't think it is the carb. The carb doesn't know the difference in starting systems. If you think it may be from the lights drawing too much current, just pull the bulbs out and give it a try.
Have you checked the intake valve clearances? Warm hard starting is one of the indications of zero intake clearance.

Ride on
Brewster

 

As Brewster suggested, valve clearance can be an issue on these and other modern 4-strokes for starting. Good point to eliminate or fix.

Jackson, no I was talking about the starter jet not the fuel/air screw cover. The starter jet on the KLX carb is really small and many have cold start problems because of it. It's definitely not his hot start problem, but he said he's had the traditional cold start problem for quite awhile, so I mentioned drilling out that jet if he was going to open his carb.