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Discussion Starter · #1 ·
couple weeks ago, i rode for 20 min. then it started to back fire and the more you gave it the throttle the worse it got and didn't want to run. i rebuilt the carb and it ran fine. took it out a couple short rides and it seemed to run great. couple days after working on the carb, i rode it for about an hour and all of a sudden it started sputtering, i was about 3 miles away and it would only stay running if i gave it full throttle.. it would sputter and max speed was about 5 mph. didn't like down hill or flat ridding trails. sputtering the whole ride home. [ it did best going up hill but max speed was 5 mph. ] . at this point the plug was fouled.... is this the same problem as before? could the carb not be fine tuned ? is there something else going on ?:blink:
 

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I'm not sure, but it could still be a carb problem. I would take the carb off and look at it again, first. Was any black smoke coming out of the exhaust when it was sputtering?
 

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Agree ^^^ also one thing I have noticed with the carbs on these sport quads is that the little metal tab that holds the choke lever on will become worn and will allow for a sloppy loose feeling choke lever. When you start the quad up and take off the vibration will actually turn the choke on to the first notch restricting the air flow causing a rich state, thus fouling the causing backfire, a hesitant throttle and fouling the plug.

To remedy this problem you can either... A. removed the choke all together (see choke Delete) in the repair and maintenance section. or B. locate another choke lever and tab possibly the dealer? To be honest I have rarely used my choke I know 400s are extremely cold nature but I run a 400 carburetor on my 250X without any starting issues. Or to save a buck you can actually zip tie the lever back just to try it ad see if that is the problem?
 

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Discussion Starter · #4 ·
I guess i will try cleaning the new plug, and ride it for about minuets then check the plug again . this should tell me how it's running,right? black - to rich, white to lean and light brown color is the color i'm looking for ? i set the piot screw at 2 1/4 turns out [ this was adjusting starting point ] and it seemed to run fine, maybe a little higher idel. have not adjusted a carb before but it was running ok. i will try the choke lever as well.
 

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You are correct with the spark plug colors. Sounds like the choke. Mine was running the same way this weekend until I realized I left the on. Dohh
 

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Discussion Starter · #7 ·
I'm not sure, but it could still be a carb problem. I would take the carb off and look at it again, first. Was any black smoke coming out of the exhaust when it was sputtering?
no black smoke ,but i did take the carb off again. well the first time around when i started to have problems, i took off the carb to rebuild, the carb was very dry inside not much gas to be found. this time there was a whole lot of gas. then i found the main jet had come off inside the bowl. it must have vibrated off. not sure if i was afraid of over tightning or what ? so i finished cleaning and puting it back together i will have to see how things work tomorrow, yikes didn't relize the time... later today. good advice again Helmut!!
 

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i may not be able to help, but maybe you can help me, I just bought a 2000 400ex and the idle is running way too high and i can't seem to spot the idle screw. Any tips?
thanks
 

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i may not be able to help, but maybe you can help me, I just bought a 2000 400ex and the idle is running way too high and i can't seem to spot the idle screw. Any tips?
thanks
Welcome to the forums. The picture below shows the throttle stop screw (idle screw).

 

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with the throttle stop screw u turn it in to turn idle down or what . mine is all rebuilt and it idles high .
 

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well i know that if you have a wire that is shorting out like against the frame or something it will do that
have a friend that had a 300ex do that
we did everything to the carb and then we looked at wires all seemed fine and then we saw a single wire hanging down and it had a cut in it
it was completing the circuit keeping the spark plug from firing 100% and once you lifted it off the frame
TA DA!!! it was like the thing came alive and ran like a charm lol
so check your wires and see if that is your problem one grounding out or completing a ciruit
 

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Yeah mine idles good cold. But when you ride for an hour it will idle REAL high. Ill take a look at all my vacuum lines and check my stop screw. Then wires tomorrow.
 
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