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06 kx250f spitting and sputtering won't stay running

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Hey guy new to the page looking for some advice my bike is hard to start by kicking it but it will start fine by bump starting then when it fires up it spits and sputters and shuts off and won't stay running any ideas ???

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Clean the carb, new plug. Probably wouldn't hurt to check the valve clearances

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Clean the carb, new plug. Probably wouldn't hurt to check the valve clearances

There is a new plug and carb was cleaned and jets were reset and still does it, think my valves need to be reshimmed?

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I would definetly check your valves . I had the same problem a few years back and found out my valves were shot and had 0 clearance.

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After you put new valves in a motor they will " set " into the seats after a few hours of high rpm's. 

The valves can set in a few thou witch can put your valves out of clearance. 

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Going through the same thing right now. I just rebuilt a 2007 from the ground up. I've checked everything. I started to go through the break-in process. Everything was working but now the bike won't kick over without the hot start held open the whole time. I'm in Maine and have had about 20 degree temperature swings. I know when I started the break-in process it was about 65 and now it's about 45-50. Am I running too lean, is the air screw that sensitive? It also doesn't seem to be getting any fuel delivery at 1/4 throttle which I feel is part of the issue too. When it was 65 the throttle would blip fine, but now at 45 degrees it won't start and if it does as I explained it won't blip. 

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On 5/5/2017 at 5:23 AM, Ride_Flip_Repeat said:

Going through the same thing right now. I just rebuilt a 2007 from the ground up. I've checked everything. I started to go through the break-in process. Everything was working but now the bike won't kick over without the hot start held open the whole time. I'm in Maine and have had about 20 degree temperature swings. I know when I started the break-in process it was about 65 and now it's about 45-50. Am I running too lean, is the air screw that sensitive? It also doesn't seem to be getting any fuel delivery at 1/4 throttle which I feel is part of the issue too. When it was 65 the throttle would blip fine, but now at 45 degrees it won't start and if it does as I explained it won't blip. 

Colder temps require richer fuel settings.  Turn out fuel screw 1/2 turn..  Raise the carb main jet needle 1 clip position.

 

Edited by FaceDeAce

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29 minutes ago, FaceDeAce said:

Colder temps require richer fuel settings.  Turn out fuel screw 1/2 turn..  Raise the carb main jet needle 1 clip position.

Think of it this way.

When cold, the air is more dense, it has more oxygen per breath.  More oxygen requires more fuel.  Richer carb/FI settings

When it is hot, the air is less dense, it has less oxygen per breath.  Less oxygen requires less fuel.  Leaner carb/FI settings.

Richer/leaner adjustments are made by a combination of the fuel screw, the needle clip position, and changing the pilot jet size. In general, a pilot jet size of 42 or 45 pilot jet will suit all main conditions on these bikes.  The stock size 40 should be reserved for those hot desert riders only.

Is it colder or warmer now than the last time the bike was tuned and was running well.  Adjust accordingly.   colder=richer, warmer=leaner.  In all cases ensure your fuel system (carb/FI) are clean and clear of any sludge or obstructions and in top tier clean condition.  A dirty system will always give a trashy hair pulling inconsistent performance.

 

 

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