7.3 Dies After Starting

[Landers Piechotka]

Buddies13 KX250F is giving us fits. It started a month or two ago when the bike started having symptoms of running lean where the idle would hang, then fall off and the bike was hard to start. The bike needs a little bit of throttle input to get it to light up, and it wont stay running no matter where we set the idle speed screw to.

The bike had low compression so we tore down the motor. Valves were smoked so picked up new valves, had the seats re-cut, put a set of rings in the motor and rebuilt. Got it fired up last night and its the same problem. Wont start unless you give it throttle, wont idle, and even when giving it throttle it dies right out after running for only a few seconds when it does fire up.

Both injectors were taken out and rigged up to a can of carb cleaner spray and opened and closed with a battery on the workbench. They are both squirting fine with no odd spray patterns or anything that would suggest a clog. Fuel pressure is good. All electrical connections are greased and plugged in.

I am thinking its TPS related since it wont start without throttle input. Does anyone know the stock values for the sensor? I plan on putting 5V to it later tonight and checking the values, but it would be nice to know what I am looking for.

Vavle timing and clearance is perfect, cam chain and tensioner are good. Filter is clean and freshly oiled, intake tract is clean as a whistle. No air leaks as it does not rev any higher when spraying starting fluid around the airboots.

I know on my Husaberg FI 450 you cant touch the throttle at all when starting the bike. If the TPS is reading any throttle input the injectors wont fire. I had thought this was across the board with all manufacturers since Keihn makes all of the throttle bodies and FI systems AFAIK... Being fuel injected it should start up in 2-3 kicks every time without touching the throttle.

Good call.. Found the problem before reading this, but it looks like somehow the vaccum line going to the MAP sensor broke. Interesting that the bike didnt rev up when starting fluid was sprayed near it, but we replaced the hose and all is good. Starts first kick without throttle input, idles perfect and runs like brand new again!

Hi I seem to have same problem replaced inlet valves and now it will only start with a bit of throttle and cuts out as soon as u let off no idle wot so ever , does this sound like the vacuum hose to map sensor?

Just had a 2013 KX250F that had been sitting for a while. would barely start and idle for a bit but cut out if you touched throttle. Turned out to be corrosion on the plug from capacitor not letting through full voltage to fuel pump.

Those TPS sensors up until i think 2015 are prone to getting water in them. Then there toast. I used to silicon seal mine and fashioned a rubber glove finger over it for added protection. Easiest thing to do is trade with a buddy on to your bike and see if it fixes it. Unfortunately they are a rather spendy part and not returnable cause its electric. So your stuck with it if you buy one. My 2011 and 2012 had the same symptoms as yours.

I have a 2012 and it will start with i think the choke ingauged and will die out in 10 seconds i would say. ive got it to stay running once but i didn't do anything special. I'm not sure what the problem is.

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