OK Im stumped, apparently so are the two dealers ive taken it too. 2002 Prairie 400 4x4 140 hours 1027 miles. Symptoms: I can ride with full normal power for about 30 minutes, then I get a slow cut in power until it starts backfiring at part throttle, works decent at full throttle, then bang, cuts out. I can sometimes feather it through the sputtering and it will then take back off at full throttle, but normally dies. It acts like the battery is low when I try to restart, turns over slower. It will then run good for sometimes another 30 minutes before it does it again.

Attempted fixes: cleaned carb, cleaned gas tank, replaced fuel petcock, cleaned out all carb vent lines, new voltage regulator (it was bad) new spark plug. im stumped. What else could it be? CDI? bad charging system killing the volt regulators? Thanks for any help. :-(

 

Clean all grounds and connections. Load test the battery. If bad, replace. Also check the out-put voltage to the battery when running. Thought it may have been a tank vent until you talked about the electrical thing. Other than that, I just don't know.

 

I would check the battery voltage when running as mentioned above. Also, if you have any added accessories, make sure you didn't mess up the grounds anywhere on the system. The battery negative is a really weak spot, if you have both the power/starter cable and a winch cable, it requires some good torque on the nut. Seems like you tried everything else. A battery may be in order. If you had a friend with the same machine, you could swap batteries and try that one before going and taking to plunge to get a new one...

 

Those 400s are liquid right? Have you checked coolant?

Probably not your problem, but I had a weedwacker that someone put straight gas into once. It ran great, started to spit and sputter then stalled. I went to pull it over and it was realllly hard. It had started to heat seize.

Might be your problem?

 

Thanks for the idea's. I will definitly check the battery, as the bad volt regulator putting out 14 volts at idle could have killed it. Coolant was full before yesterdays ride, but ive never cracked open the system and its never gotten too hot. Overheat indicator has never come on. Back to this tank vent, if I take the cap off, should I be able to blow easily through the tube on the cap? I cant on mine.

 

what is the spec for voltage output at idle ????? I am not familiar with the atv's but on a car that would be normal.

it does sound like an electrical problem though.

Is there anyway for you to check the charging system when it acts up to see what the output is ???

when its noticeably dieing put a multimeter on it and see what output is ?

it could also be possible that your charging system has enough volts but has no or little amperage output therefore you would be able to ride until the battery went weak.........
which is what would happen on a car.
look towards stator or altenator which ever it runs if that was the case.
I wish i was more familiar with the atv because I know some can run without the battery in them so that would eliminate the whole battery theory .

but if it was me walmart sells batteries fairly cheap I might just throw on in it for piece of mind

wish I was more help

 

The dealer changed the regulator they said it was a solid 14 volts all the time, and wasnt changing with idle, I guess its supposed to change with engine speed?

I do know from a previous incident, that this machine will not run good with a dead battery, I had a stator wire problem that killed the first battery halfway though a trail ride, I pull started it, and it sputtered all the way home. New stator and it still sputtered until I got a new battery. This time it has the same symptoms. However it cranks normal if I shut it off myself before it gets to the point of dying. Maybe its just battery time, but now you guys have me curious. Im will rig up a volt meter and maybe an amp guage to the battery connection and go for a ride next week, that should provide some insight.

 

Sounds like the coil .

 

.. Definately sounds like an electrical problem-- something getting warm and building up resistance then bye bye. Possibly the rectifier, though those hardly ever go south, but woth a look...

 

Sounds like you're not positive the tank vent is working properly. So next time you're out riding, as soon as it starts acting up, just open the gas tank cap and see if it makes any difference.