Sportsman 400 running poorly and confusing me to death...please help

[krausemouse]

Bought used 2004 Sportman 400. Owner claimed ran great before it sat for long time. Drained fuel and replaced with new plus fuel treatment. Didn't help after running about 15 miles of fuel through it.
Starts and idles fine. Runs mediocre when cold at low speed, not at higher speed and rpm (blubbers and craps out). After 5 minutes of running barely OK, it gets warm and barely runs. If put choke on, it quits. It runs much better when airbox cover off… but still not great.

Cleaned air filter, replaced cracked carb rubber boot going to airbox and airbox rubber seal. Thoroughly cleaned carb and all jets. Seemed clean to start and all jets and passages seemed clear. Put back together and leaked much gas into motor, leaked out exhaust pipe. Perhaps float stuck so I removed carb again and re-assembled. Put in new plug after drying out for the night and still runs poorly. Removed fuel pump and diaphram and check valves all seemed OK. Working with mechanic much smarter than me and we're both puzzled. Anything else we should check?

Appreciate any help you can give

[KAWIRYDER]

It sounds to me that you are running to rich in the fuel department. You might try messing with your fuel air mixture screw or lean your main jet out. I have tried to get help on this polaris site and nobody really helps you, so maybe try powertrain or maintenance section of site. Hope this helps.

[rundrave]

try adjusting the throttle cable, you can also take off the cover on the throttle assembly on the handle bars. there is a ETC (electronic throttle control) that has 2 metal contacts, when they touch it causes the machine to die, these are adjusted buy adjusting the throttle cable.

make sure you route the throttle cable correctly. On my 500 there is a channel along the side of the gas tank, make sure its not kinked or anything abstructing it.

My quad was acting the same way, idled great and ran great when it stayed running, but it would just randomly start acting up and i had taken the gas tank off to get to my plug, when I put everything back together I didnt route the cable right and I figured this is what caused it.

also this is a CV carb, you have to maintain a certain amount of vacuum for it to operate right. It takes resistance on the filter side of the carb to pull the slide up, not sure EXACTLY how it works but from what I can gather it has to do with velocity through the carb that pulls the vacuum to operate the slide.

[xjoedirt55x]

Sounds to me like it is some sort of air/fuel or vacuum problem. First step is to definently check everything going in and out of the carb and make sure everything is unobstructed and connected properly. Check the throttle system, and if none of that works, I would say that the carb is out of whack. What octane fuel are you running?

[krausemouse]

I am running 89 or 91 octane. Not sure what I put in. I'm getting some good advice on what to look for. A lot of people have mentioned looking at the throttle cable. When I took the carb apart (twice) the cable action seemed good and I tried it to see that the butterfly was opening and closing crisply. Other things that people have recommended I try are: new needle and seat since it leaked gas so badly into the motor; new fuel pump rebuild kit; change oil as crank case oil may be very full of gas; reverse override switch -check to see that it's not limiting forward revving. Possibly rejet leaner if all the fixes don't work; check the timing with a timing light to see if it fluctuates when it's running poorly. I plan on putting a new needle and seat in this weekend and likely rebuilding the fuel pump as well. After I'm sure it's not leaking again, I'll change the oil and run it some more. Thanks for your thoughts and please give more if you have them

[jhoppa]

Check all your breather hoses going to your carb. They might be plugged with mud/dirt. If the vent hoses are plugged you get the same type of poor running at higher rpms.

I cut mine at 45 degree angles and then cut a split about 2 inches long so there is less of a chance to get clogged.

Check the connection opposite to carb, under the ATV. :D