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I have not been riding this year but would start my 450x every few weeks to keep everything working. A few weeks ago after it was running for about 30 seconds, fuel started to come from one of the carb vent tubes. I shut the fuel valve off and then the bike about 30 seconds later and left it. Next day without starting the bike, I opened the fuel valve and in about 20 seconds, fuel started coming out again. Left it alone again. Last week when I went to show someone my bike, I started it and although I was expecting fuel to come out, none did. Let to run for a couple of minutes and even left the fuel valve open after shutting it down. No fuel while I was doing other stuff in the garage. While I know problems usually don’t fix themselves, I figured great! Took it out for a ride and got about 1/2 mile away and it started to break-up and then shut off. It tried to restart but wouldn’t stay running. Pushed it back and when I was at my garage, I tried again. Started and idled fine. Went to ride it 200’ and it shut-off. I removed the jet access plug expecting to find crusty particles from ethanol fuel but it was all clean including the main and pilot jet. Used a mirror and flashlight too. Assembled it and still idles fine, can rev into the rev limiter but occasionally it will shut off like the kill switch is pressed. I pulled the fuel line off the valve, flows great. You know how hard it is the pull the carb off only for that to be all okay. Any chance I could have a bad CDI module?

Well the first problem sounds like a bit of trash in the needle and seat or a sticky float. Sounds like it is good for the moment.

Your second issue, well you said it yourself, like the kill switch cutting in.
As a temporary test, disconnect the kill switch and see if that fixes the problem.
Wouldn't be the first time one went faulty.

Also make sure the breather for the fuel tank is free.

Let us know if that helps things.

I agree with the sticky needle and seat. It is unlikely that it is self healing, but sometimes, whatever the culprit is just falls out and everything is golden. Did you go to church on Sunday?

I would start with a basic fuel flow test. Gas cap off, container under the float bowl drain, open the petcock, and loosen the bowl drain screw. Steady stream of fuel draining out for a minute? Then, put the gas cap on and try the same thing again for even longer. We're trying to rule out a plugged gas cap vent.