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Discussion Starter #1
I just bought a 2000 400ex and it's giving me a problem with the thumb throttle. The throttle is completely fine when shut off, but only gives me a hard time when riding. When I push it, sometimes it stops at half throttle and I have to press it harder to get it to go the rest of the way. It feels harder and isn't as smooth as I feel it should. It almost always gets caught at half throttle and I have to press it harder to get more throttle out of it.
 

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There are two possibilities. One is the throttle cable is coming apart and snagging. The 2nd is the carb is worn out. The slide is pulled against the body from vacuum and can wear the sliding surfaces. This wear can be multiplied if dirt enters the throttle bore. I hope this isn't the problem because new carbs are expensive..........don't buy aftermarket/chinese carbs.......too many complaints about those on this forum. There is a very minor chance that the thumb throttle mechanism is worn out too but much less likely than the first two suggestions.Hope this helps!
 

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Discussion Starter #3
There are two possibilities. One is the throttle cable is coming apart and snagging. The 2nd is the carb is worn out. The slide is pulled against the body from vacuum and can wear the sliding surfaces. This wear can be multiplied if dirt enters the throttle bore. I hope this isn't the problem because new carbs are expensive..........don't buy aftermarket/chinese carbs.......too many complaints about those on this forum. There is a very minor chance that the thumb throttle mechanism is worn out too but much less likely than the first two suggestions.Hope this helps!
Right on, I checked the cable and it seems to be fine. So you are thinking it's the carb? How much would one run me? Do you happen to know by any chance?
 

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Does your throttle contact any part of your hand grip during it's travel?
 

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Discussion Starter #5
Does your throttle contact any part of your hand grip during it's travel?
No, it only does this when the quad is running. When it's shut off, it moves completely smooth like normal but when I take it for a ride it does it...
 

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Don't buy any parts until you identify the problem, cause as misterclean59 said, its likely to be one of three possible things. I'd take the thumb throttle apart first and then check the cable and related hardware. Make sure the cable is not kinked or twisted or routed around tight corners where it doesn't belong... and that it is adjusted properly and has sufficient slack. Once you've eliminated those two, open the carb and look it over for loose screws on the throttle butterfly (loose screws can and will be ingested if ignored) and for deep wear on the slide. You do have a copy of the FSM right?

Let us know what you find out if ya can... and welcome to the forums!
 

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Welcome to the forums. These guys have you in the right direction. I would make sure the cable is routed over top of the heat shield under the tank if it's getting hot the cable could be binding. also the slide could be loose (seen this a lot ) the top of the carb would have to come off to check the 2 small screws holding the actuator arm to the slide. In the throttle assembly there is a nut holding the thumb mechanism in place I have seen the loosen as well and cause a throttle to hang wide open.
 

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Discussion Starter #8
Welcome to the forums. These guys have you in the right direction. I would make sure the cable is routed over top of the heat shield under the tank if it's getting hot the cable could be binding. also the slide could be loose (seen this a lot ) the top of the carb would have to come off to check the 2 small screws holding the actuator arm to the slide. In the throttle assembly there is a nut holding the thumb mechanism in place I have seen the loosen as well and cause a throttle to hang wide open.
The cable is routed the way you described. Didn't have time to check anything else today.
 

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Discussion Starter #9
Don't buy any parts until you identify the problem, cause as misterclean59 said, its likely to be one of three possible things. I'd take the thumb throttle apart first and then check the cable and related hardware. Make sure the cable is not kinked or twisted or routed around tight corners where it doesn't belong... and that it is adjusted properly and has sufficient slack. Once you've eliminated those two, open the carb and look it over for loose screws on the throttle butterfly (loose screws can and will be ingested if ignored) and for deep wear on the slide. You do have a copy of the FSM right?

Let us know what you find out if ya can... and welcome to the forums!
Right on, throttle assembly seems to be working correctly and the cable seems adjusted right and routed correctly. Whenever I find time next, I will take a peak into the carb and see what it looks like.
 

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Discussion Starter #10 (Edited)
Ok, I am stumped. I opened up the carb and it seems to be working how it should. I don't get how shut off it works fine, but only does it when I take it for a ride.... Here's a video to show what its looking like
 

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Discussion Starter #11
Also got this video, when I hold the throttle wide open, the black slider isn't wide open and I can move it with a screwdriver. Not sure if it should open all the way or if it's working as it should
 

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Hmm.... I would have thought your carb would have been the problem.... try spraying WD40 into the cable and just push the throttle wide open and close.. wide open and close... Try seeing if that will help... otherwise I'm stumped on this one... hopefully you will get it figured out... Good luck
 

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Hmm.... I would have thought your carb would have been the problem.... try spraying WD40 into the cable and just push the throttle wide open and close.. wide open and close... Try seeing if that will help... otherwise I'm stumped on this one... hopefully you will get it figured out... Good luck
Well, after having the carb apart twice, I fixed it.... not quite sure what I did LOL, but it's working perfectly now!
 

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Hmm.... I would have thought your carb would have been the problem.... try spraying WD40 into the cable and just push the throttle wide open and close.. wide open and close... Try seeing if that will help... otherwise I'm stumped on this one... hopefully you will get it figured out... Good luck
Well, after having the carb apart twice, I fixed it.... not quite sure what I did LOL, but it's working perfectly now!
Glad to hear you got her back on the road :icon_ banana:
 
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