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Rucurring issue...Help please

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Background...06 KX450. Rebuilt the motor back in June and the first weekend I went riding about an hour and a half into the riding I came up short jumping a gap and the bike started popping and would not stay running unless I was on the gas. If it died it was very hard to restart. I took it home and cleaned the carb and blew out the jets and it worked fine after that. Started first or second kick every time. Race at Glen Helen in September bike ran fine during most of practice then started popping coming down Mt. St. Helens and died at the bottom. Got it retarted and made another lap and died at the top of MSH. took it back to the pits and cleaned the float bowl out and richened it up half a turn. Ran well the rest of the weekend. Race this last weekend it would not start in the morning. Missed all of practice cleaning the carb and adjusting to get it to start. Ran fine. got the holeshot and led for 2 laps and then... bad popping on decel, bike dies and won't refire. It's sitting in the garage right now as I lick my wounds from what might have been my first win:banghead: The holeshot and first lap were that good... Any ideas? I am going to clean the carb again, add a fuel filter again(had one previously but it melted the inlet and outlets and restricted flow.) clean the tank. I will also have the valves checked and adjusted, but since the problem seems to come on suddenlyI think I am looking at dirt in the fuel.

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You may have a bad one way vent in the gas cap. Replace it to be safe.

Sounds like it sticks at times.

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You may have a bad one way vent in the gas cap. Replace it to be safe.

Sounds like it sticks at times.

Did not even think of that. Thanks, I'll check that as soon as I get home. :busted:

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If it's not a fuel starvation issue, it sounds like a stator issue.

Yeah. I'll search the site for info on checking the stator as well. I will say, I removed the vent hose last night and the bike started second kick....:busted:

It's time to do all my end of year stuff anyway, so I'll pull it all apart and clean and lube everything and get ready for next year.

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Yeah. I'll search the site for info on checking the stator as well. I will say, I removed the vent hose last night and the bike started second kick....:busted:

I had an issue like that last year. Hard to start, then would die on the track. Couldn't figure it out. I removed the shorty vent tube with the metal tip and put a regular hose on it. Solved my problem.

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I had an issue like that last year. Hard to start, then would die on the track. Couldn't figure it out. I removed the shorty vent tube with the metal tip and put a regular hose on it. Solved my problem.

Probably the issue. That's the same one I have and now that it's gone it starts and runs fine. Man I feel stupid...I'll just finish checking everything out to be sure. What a waste. I appreciate all the info guys. I would hate to think of how mad I'd be if I went through all the other steps and had the problem re-occur because I didn't eliminate the shorty vent.

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Update: Went riding this weekend and problem occurred again:bonk::lol:

As I was riding and it began to die I grabbed the gas cap and loosened it for a second...the problem went away...

Went home, removed the cap and took it apart. Inside up at the vent hole there was a small plug of some resin looking material. I picked at it with a screwdriver and it flaked out in crystals and uncovered the hole. It was clear and like I said looked like plastic resin. The bike ran fine for a long time, so I have to imagine that this was a recent development. Replaced the cap with another one anyway so all should be good. Weird though...

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Excellent. Vapor lock is what they call it. My shorty vent tube over the years eventually got clogged but you couldn't tell by looking at it. Hopefully you're good to go now.

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Excellent. Vapor lock is what they call it. My shorty vent tube over the years eventually got clogged but you couldn't tell by looking at it. Hopefully you're good to go now.

Dumped the shorty a few days before I went riding. I was surprised, to say the least, to have the problem come back. Should be all good now, but I have the bike torn down for winter maintenance. New rims, clutch, adj valves, lube all bearings, etc. back up and running in January. I'll know for sure then.

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