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Discussion Starter #1
I'm working on an '03 400 for a friend of mine that will not rev up over 20 mph. It only has 980 miles on it. It was running fine one day, then the next morning it would not rev up past 20. It just pops, sputters, and back-fires once it gets there or anything past half throttle, but up to there it will run perfect. It also revs just fine up to the rev limiter when in neutral. I have drained the fuel, checked the carb for anything in any passages, jets, and bowl. Everything was clean and the jets are stock. The diaphram on the slide is fine with no tears or holes and the needle is fine. The choke is working properly and not hanging up. I have checked the valves and they are fine. The spark plug is black, which is a sign of over-fueling, or not enough air flow. The air filter is in great shape, and the exhaust seems to not be obstructed. I turned the headlights on while driving it incase it was overcharging and nothing changed. I also pressed the override button to see if it would make a difference and it didn't. I swapped the CDI out with the one on my '04 400 and still no change. The quad runs fine right up until about 20 mph or 1/2 throttle. I've checked and tried everything I know to do. I'm open to any and all suggestions.

Thanks in advance,
C.J.
 

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wow...for your first post, this is a home run of a post! VERY good detail. I'll have to think about this one.

Just for kicks, did you try a new plug wire and plug? It's a long shot, but maybe there's a breakdown in one of the components that will allow lower amounts of voltage, but not higher? Again, it's a long shot but considering everything you've tried, might be worth looking into.


Another question...is it an auto or manual? If it's an auto, could it perhaps be in limp mode where it limits the speed due to a detection of a belt issue? The 650 V2's have this, and it limits you to roughly 10mph.
 

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Check the stator wires coming out of the left side case. They run under the exhaust, so be careful where you put your hand. You should be able to tug on them while the ATV is idling and listen to the motor. If it misses or hesitates then you probably have a stator wire shorting against the motor. I had a couple friends with 400's that did this, the wires slide from the grommet and the engine case rubs thru the insulation.

To fix it you have to remove the side cover to repair the wire........Not fun!
 

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Hmmm, your problem sounds just like mine on my 500. I have cleaned and re-cleaned the carb and it runs and idles fine when it is stationary. But as soon a you start driving it then it starts to sputter and miss. I would check the wiring if I were you.......I might just do that myself.
 

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Sounds like a main jet plugged or something, doesn't it? Clutch not shifting out?
 

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Discussion Starter #6
I forgot a few things that I checked. The vent on the tank is fine. I also clipped 1/4 inch off the end of the plug wire to make sure it wasn't corroded. My last attempt before posting this was to change the plug, still no difference. It is an auto, but the 400's don't have a belt switch. Good idea on the plug wire Sanny651, I'll check that and possibly swap the coil off of my 400 onto his. Claws, I'll have to check that rubbing problem also. I had not heard of that problem yet. I'll keep you guys posted on what happens, I should have some time to work on it tomorrow. Thanks guys!
 

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You have my curiosity peaked man...wonder what the issue is. Didn't know about the stator wiring...great suggestion Claws! I too was thinking of a clogged main jet, but since you had already checked that I dismissed that. Plus, your plug was black so you are getting plenty of fuel...something with the spark or air is juked up, and since your air passages were checked, we're down to spark.
 

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maybe the choke cable is blocked, try to move it when your engine run to see if the idde change
 

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I just had a similar problem minus the popping and backfiring. I put a jet kit in and somehow the cover on top of the diaphragm didn't seal perfectly. The quad ran 24 mph tops. I knew right away what had happened and removed the carb completely this time. Its easier to work on carbs on the bench than inside the frame........tigger
 

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Discussion Starter #10
Just thought I'd let everyone know that the problem was the passageway, halfway up the carb, on the air filter side that leads to the main jet shaft was plugged off.
 

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'04 400 Auto with the same symptoms, only mine will make 25-30 MPH.

Was working on the float level to stop fuel from running out the dump tube and ended up sputtering on a test run. More fiddling and no change. Figured it was the main jet, so I removed it, hit it with air, put it back and had the same problem. I was starting to sweat a belt problem until I dug up this post. Time to actually pull the carb out instead of just rotating it to pull off the bowl.

Luckycowdog: You came here looking for help and ended up helping others. Thanks.
 

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Wont rev over 20 mph

It may be you timing chain, im only 15 but i think this might be it cause mines doing the same thing... Mines a 2002 arctic cat 500i 4x4 auto wont rev past 10mph...
 

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Mine is doing same thing. (With both engines) i got a whole used engine and new carb plus just replaced the stator in the engine after changing engines out. Still doing it. Don't know what to do
 

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Start your own thread would be the best bet.
 

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i have the same problem cleaned carb 3 times and i cant find tgat jet you cleaned do you have pics please help
 

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