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400 wont run without the choke on

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My 400 was running great a month or two ago, but now it is really hard to start in the morning and once started it will only run with the choke on and when I finally do get it running it is sputtering and popping like mad!  Any ideas?  I already checked the jets and they are clean...

 

- Ben

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Pilot jet is clogged. Its sometimes hard to see because its such a small orifice. If you're having trouble just replace the jet.

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+1 on the clogged jet.. Time for a good carb cleaning.. Next time run or drain the carb before you store your bike.

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I am pretty sure the pilot jet is clean, I used a welding tip file to clean it.  

 

I could see it being the gas situation.  I was having some trouble with my either my float sticking or the float valve leaking, not sure which, so I adjusted the floats down to put more pressure up on the valve.  It ran great for almost a year like that, but the other day I had my bike on its side to work on it and then realized that I didn't turn the gas off, but yet it wasn't leaking everywhere.  SO I will try adjusting the float.  Thanks for the tip.

 

- Ben

Edited by shine13

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Seems like Kalifornication. The ethanol kills pilot jets.

1. Buy a new pilot jet. $5-8. It's really hard to properly clean them. I no longer try.

2. Add a fuel filter.

3. Make sure your gas cap vent hose isn't plugged. Reminds me I need a new one way valve. Mine is plugged.

4. Make sure you don't have an air leak. The manifold gasket oring can get kicked.

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I used a welding tip file to clean it.  

 

It's most likely a different size now.  There is less than .001" difference between each jet size.  If larger, though, it wouldn't cause you to need the choke on.

 

The fuel screw and it's passages may be damaged or clogged.  This could cause you to need the choke.

 

The air leak around the intake manifold is another possibility.

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Well when I pulled the manifold the gasket was broken, so maybe that was it.  I'm going to try, 1)changing my float position back to where it was, 2) replacing the pilot jet and 3) replacing the manifold gasket.  I anticipate putting it back together, having it run flawlessly and never really knowing which fix was the actual problem.  :ride:

 

- Ben

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