KX 125 w/ Mikuni dying *Fixed*

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1/20/2018 5:35 PM
Edited Date/Time: 1/20/2018 5:43 PM

I have a 2005 and after it runs for approx 2 min it dies. I turn the fuel off, purge the inlet hose from tank, turn back on and it fires up and runs awesome then dies again after 2 min or so. I’ve cleaned the carb thoroughly so I know it’s not a plugged vent line. Does it with or without cap on the tank. Anything else I can check?

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1/20/2018 5:50 PM

Clogged filter in the tank?

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1/20/2018 5:55 PM
Edited Date/Time: 1/20/2018 5:56 PM

Tank flows fuel like a champ all the way to the carb. It has to be something with the carb but I don't really know what else to check. The carb is getting fuel but it's like it is getting vapor or air locked while in there....

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1/20/2018 6:04 PM

Ignition problem?

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1/20/2018 6:09 PM

I don't think so. The first time it did this, I thought I had fouled a plug. Looked good, checked it and spark was not an issue.

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1/20/2018 6:10 PM

Plugged float bowl vent lines. Also check the fuel tank vent line.

Paw Paw

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1/20/2018 6:11 PM

I will add to this, it's only does this once it is at operating temperature and under load. It can sit there on the stand and idle for 30 minutes.

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1/20/2018 6:13 PM

Paw Paw 271 wrote:

Plugged float bowl vent lines. Also check the fuel tank vent line.

Paw Paw

Hey Paw,

I put carb cleaner and compressed air through every single orifice In the carb. Jets are cleaned with tip cleaner. Blew backwards through the tank vent to make sure it's not the tank that's vapor locked. Even rode around with the cap off.

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1/21/2018 6:58 AM

What else could cause carb not to flow fuel?

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1/21/2018 8:03 AM

Did you check the carb float bowl vent lines that I mentioned?
Have you done an ohms test on the ignition coil on both the primary and secondary sides. If so, what were the readings? A coil can break down even with showing a good spark at start up. When this happens your loose spark then when the coil cools down the spark will return.

Paw Paw

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1/21/2018 10:42 AM
Edited Date/Time: 1/21/2018 10:56 AM

Paw Paw 271 wrote:

Did you check the carb float bowl vent lines that I mentioned?
Have you done an ohms test on the ignition coil on both the primary and secondary sides. If so, what were the readings? A coil can break down even with showing a good spark at start up. When this happens your loose spark then when the coil cools down the spark will return.

Paw Paw

Paw,

Yes I replied to your first response lastnight, thank you. When you say ohm out the coil, are we looking for a resistance measurement or just continuity across the circuit? I will ohm our the ignition, but I still feel it’s fuel related. The second I relieve the head pressure from the carb inlet, it starts first kick. I have it down to where it only is dead for 5 seconds. Lol. Thanks in advance!

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1/21/2018 11:24 AM

I still don't see where you checked the carb float bowl vent tubes. If they are blocked it will stop the fuel flow as the fuel used will create a vacuum in the float bowl and the fuel flow will stop.
RE: coil....Yes the resistance readings.

Paw Paw

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1/21/2018 11:45 AM
Edited Date/Time: 1/21/2018 11:46 AM

Paw Paw 271 wrote:

I still don't see where you checked the carb float bowl vent tubes. If they are blocked it will stop the fuel flow as the fuel used will create a vacuum in the float bowl and the fuel flow will stop.
RE: coil....Yes the resistance readings.

Paw Paw

At this moment in time, the carb doesn’t even have vent hoses on it, just the nipples. Thursday, I pulled the carb completely apart and put carb cleaner and air through every single oriphice I could find in the carb. Still no luck as of yesterday afternoon.

I will also put my meter on the bike and ride around and see what’s happening voltage wise when it dies.
For trouble shooting purposes, I guess I could pull my carb off my cr and see how it acts on the bike. Process of elimination.

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1/21/2018 11:55 AM

Also, this is the first time this bike has ran since I've owned it. It might have 30 min on it total. Been building it for the last 6 months after buying it in a box, half tore down, missing all kinds of shit. That being said, I have no idea how or even if the bike ran previously in its life. Thanks for all the replies so far.

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1/21/2018 2:59 PM

The carb needs those hoses.
Also check that coil.
Also pull the fuel petcock and check the filter screen on it.

Paw Paw

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2/3/2018 12:48 PM

Not trying to bring up a dead thread, but it may help someone who is stumped. The problem I was having with this carb was that the o-ring for the float valve seat was worn enough that the seat was moving with the valve.

So as soon as the float filled the bowl, the seat moved down with the valve and wouldn't let more fuel in until I pulled the fuel line off, and it got a gulp of air to reset the float and fill the bowl again.

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