2011 YZ450 will start, but then dies

The bike is 9 months old and has 35 hours on it. I have never had any mechanical issues with it. All stock except for foot pegs and bar risers. I haven't ridden it in 2 months and took it to the track yesterday. Rode fine for 30 minutes. Then it started dying when I came to a stop with the clutch pulled in. Then it got worse where it would start and then die 10 seconds later.

Is it possible that the gasoline went bad? My gas container has gas probably 3 months old. I filled it up while I was riding. Maybe the gas that was in it was OK, but as I added gas from the container, the proportion of bad gas increased making it run worse and worse? The other thing I noticed before having stalling problems is that the kill switch seemed like I had to push it down more to stop the engine, maybe the kill switch is going out. Any ideas?

I would try dumping the gas out and putting some fresh gas in as gas doesn't store very well anymore and even worse if it has ethanol. Gas with ethanol attracts water, so if you live in a humid area you could have quite a bit of water in your fuel.

clean the pipes hoses check fuel pump that should get you going

Ethanol, like all alcohol, absorbs water, and it will pull in from the air if it's exposed to enough damp air long enough. The upside, though is that if the alcohol in the fuel absorbs the water, it will at least flow through the system freely and not clog things up the way it does in straight gasoline. In fact, a pint of alcohol in the tank is a standard method of chasing water out of a contaminated fuel system. Water in the alcohol in the fuel does degrade the energy content of the gas, though, and can cause the kind of problem you're complaining of. Fresh fuel is a good place to start.

Just swapped the gas out and here are the symptoms:

Very hard to start

Back fires while I am kicking it over

When does start, I have to keep the throttle open or it will die (won't idle)

Now I'm thinking it needs valves adjusted...would that be the next thing to try?

It never hurts. And yes, tight valves can make the bike "cranky" when cold. Is your compression low?

Yes, when I kick it, does feel like less compression.

Check the clearance.

My mechanic says it is the fuel pump (just tested with another fuel pump). Any ideas how it could have gone bad so soon? Could bad gas have contributed?

Could it have been a bad/corroded/dirty connection to your fuel pump.

Yes, when I kick it, does feel like less compression.

how would you get less compression from a faulty fuel pump? or was it just in your head lol?

Yah, it was in my head I guess :bonk:. I think it was because I was kicking it so much it started feeling light. It has started on first or second kick since I bought it. Bike is running good now that fuel pump was replaced.

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