I have a 2010 500 ho and it seems every time i run it, for the first half an hour it runs great. If i stop it and restart it after a few minutes, it runs like crap. Bogs on part acceleration and on full acceleration at times. Most of the time i can throttle it to keep it running great on the trails unless the tank is full.
Things i have done:
Changed the carb. Float is set right, needle and seat seal fine.
Heat shield on the bottom of the gas tank.
Sprayed the intake boot with brake clean, no change in idle characteristics.
New plug, new coil, new pickup coil.
Stator checks out, battery seems good.

Things i have noticed:
Fuel bubbles out of the vent line. I have blown into this line and can hear air going into the tank. (Seemed obvious since fuel is coming out air would go in but, i checked anyway)
Full tank is worse than half tank of gas
If I throttle it from Idle-WOT i can continue riding
If i go into water, it almost dies (steam being sucked in?) then goes back to bogging once i exit the water
At WOT the airbox cover seems to get sucked in (compression must be ok if i am getting vacuum, right? All good, it pulled 90PSI.)
If i turn off the fuel, as the carb carb bowl empties it gets better and runs flawlessly until it runs out of fuel.
The tachometer is nowhere close until an electrical load is put on the system (ie lights) (14.5V on idle)
Stator seems to check good.
Fuel pump seems good since, if i shut off the fuel, it ends up running better so it must be pumping and works mint for the first half hour.

It's got me stumped. Anyone experience this?

Lastly, i tried pulling a rzr out of the mud and the drain from the winch was so bad it shut the bike off. I assume this has more to do with duration of winching time/weight of the rzr than a bad battery/stator. But, if you have any insight i'm all ears, er, eyes. lol

Thanks
Adam

 

If there is a thread on here that someone can point me too (i must not be typing the right buzzwords) that would be appreciated

 

i'm going to start spitballing in this thread to see where it leads.

So, I know when I shut it off to take a break with the boys, the fan shuts off and all the heat traps inside the engine area. (Runs good until then (55mph, all throttle positions are working)
I go to start it after this break, starts fine, idles fine. Won't rev, especially under load. Close the fuel petcock, runs like crap for a bit and as the carb bowl empties it runs better and better until it runs out of fuel, turn the fuel petcock back on and it goes back to running the same way. Like crap. Although, most of the time I can snap the throttle WOT to idle back to WOT and continue this and finish the ride (as long it takes, we are talking hours it will still run like this, throttle on , of, on , off) Now, i am assuming that gas is filling the carb to the point of overflow, for whatever reason it doesn't do it at all cold. When I'm in the bog situation, if I go into water that is up to the carb overflow drain, then it really runs like poop, until i am out the other side of the water, then back to regularly scheduled bogging.
Another thing, if i slowly increase the throttle, as the rpms rise, i can add a bit more throttle but, this only works up to a certain throttle position then the bog kicks in again (usually extended WOT will bog it out, then let off and WOT)

So first, what is the heat doing to make it run like this? Heating the plastic carb float causing a malfunction? Is it cooking the gas and giving the float a false sense of closed and fuel keeps pouring in? if this were true wouldn't emptying the bowl clear the issue?
Is the tank building pressure from the heat and forcing the fuel past the needle? if this were the case wouldn't clearing the fuel out of the carb fix this? Or taking off the gas cap?
Why does it do this worse with a full tank than an empty one?
Is there a loss of compression when it's hot? How could this be? the aluminum piston expands more than the cast iron cylinder sleeve right? it doesn't blow by or burn oil either. (Not to say the oil rings are good and the compression ring is bad) the compression is within spec.
Is the spark control breaking down (CDI)? How could it? It's well out of the heat zone and don't those either work or don't?
Could this be a head gasket failure? Well, there is no coolant leaking out and no white smoke out the muffler.
Could the valves leak when hot? That would be some pretty serious warpage or flex to return to normal when cool.
Could the cam be worn? Wouldn't it do the same all the time.
Could the cam lobes and valves expand to push the valve partly open? Doesn't sound possible if you set the rocker arms to .006" spec cold. Does it?
Could it be leaking past the fuel pump? Quite possible but wouldn't it stop at the needle and seat?
Voltage regulator? Only when hot? Seems unlikely. Especially if it gets worse in water.
Stator? Possibly, not likely though.
Water pump or coolant circulation? the temperature light doesn't ever come on. This isn't iron clad excuse of the water pump but, when the water pump quits on a car it overheats. I assume the same for atv's.

I'm going to continue to do some "what if i do this, how does it respond?" type of riding this weekend and report back.

Cheers