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Thread: 400EX Won't Start

  1. #1
    Join Date
    May 2013
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    Central KY
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    400EX Won't Start

    So I'm trying to help my brother in law out with his '05 400EX. It died while riding it and now won't start. I thought a spark plug would be a quick and cheap idea so I changed that and still nothing. The starter is spinning and the starter clutch is catching because I could see the piston moving while I had the spark plug out. I'm thinking it's something in the electrical system but I'm not great with electrical stuff. What should I check next? Any help is greatly appreciated.

  2. #2
    Join Date
    Jul 2013
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    366
    I'm sure you've already checked but does it have gas? Lol but it sounds like electrical to me Check the fuse back by the battery
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  3. #3
    Join Date
    May 2013
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    Central KY
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    Sadly, it has gas. When he told me it wouldn't start, the first thing I checked was the gas.

  4. #4
    Join Date
    Sep 2012
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    177
    check to see that the plug is sparking. put it in the wire and hold the "finger " on the header. thwn turn it over and watch for a spark at the tip. if it has spark check compression, incase you dont have a compression tester that will fit i reccomend harbor freight. they have a 3 piece compression tester with interchangeable sizes. they are 30-40$
    2003 400ex
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  5. #5
    Join Date
    Dec 2010
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    Quote Originally Posted by Drifterboy3 View Post
    check to see that the plug is sparking. put it in the wire and hold the "finger " on the header. thwn turn it over and watch for a spark at the tip. if it has spark check compression, incase you dont have a compression tester that will fit i reccomend harbor freight. they have a 3 piece compression tester with interchangeable sizes. they are 30-40$

    Yes...check if it has spark. If it does, put plug back in and throttle it a bunch like your trying to flood it while hitting the start button....now take out the plug, it should be wet with gas....if the plug is dry your not getting gas. You cab also shoot a little gas down the plug hole and if it has spark it will ignite and run a split second. Let us know if you have spark and gas.
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  6. #6
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    May 2013
    Location
    Central KY
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    Will check it this afternoon when I get in from work. Good place to start. Thanks guys. I'll let you know what I figure out.

  7. #7
    Join Date
    May 2013
    Location
    Central KY
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    It has spark. I put the plug in the boot and touched the electrode to the header. Hit the starter and it was sparking. I put the plug back in and tried to turn it over quite a few times while punching the throttle. Pulled the plug back out. It was hard to tell if it was wet or not where I had anti seized the threads. Should it have been noticeably wet with gas? Either way, I went ahead and took the carb off. Just out of curiosity I left the throttle cable attached and took it to full throttle a couple of times. It squirted gas out of the engine side. So that should mean it's getting fuel, right? What should I check now?

  8. #8
    Join Date
    Sep 2012
    Posts
    177
    Yes it is getting gas. That's the accelerator pump. I would check compression now.
    2003 400ex
    powermadd star series handguards w/wrap-powermadd gauntlets-elka stage 3 front shock-tusk nerfs- 11:1 piston-full fmf-gtt xc link-oury grips-909 bars-precision anti-vibe clamp-K&N filter-ccp steering stabalizer-oversized oil tank

  9. #9
    Join Date
    Sep 2012
    Posts
    177
    As the motor turns does it sound like it "pumps" or does it just sound like it's turning?
    2003 400ex
    powermadd star series handguards w/wrap-powermadd gauntlets-elka stage 3 front shock-tusk nerfs- 11:1 piston-full fmf-gtt xc link-oury grips-909 bars-precision anti-vibe clamp-K&N filter-ccp steering stabalizer-oversized oil tank

  10. #10
    Join Date
    May 2013
    Location
    Central KY
    Posts
    31
    It doesn't sound like normal. I at first thought maybe it was the starter clutch because the starter sounded like it was spinning at a much higher RPM than normal. But once I saw the piston was moving, I started looking at other stuff. Couple of questions: can I rent a compression tester? And what would cause it to just lose good cylinder pressure? It started just fine and was running, then just died and wouldn't refire. Head gasket? It's not got any oil or anything leaking out between the head and cylinder.

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