Gets hot, runs horrible and then stalls and won't crank
 

I have a 1995 Yamaha Warrior 350. My problem is when it gets hot (5-10 min of riding) it runs like crap (starts to break up) and then it will stall and won't crank til it cools down. http://images.ibsrv.net/ibsrv/res/sr...es/biggrin.gif Any info would be much appreciated.http://images.ibsrv.net/ibsrv/res/sr...milies/nod.gif
We have put a new air filter, oil filter, oil, and cleaned the carb on it.http://images.ibsrv.net/ibsrv/res/sr...milies/huh.gif

About the only way to get an air cooled engine hot is to have it really lean.
What does the plug look like?

It just sounds lean to me.

Do you mean it cranks over, but won't fire, like no spark? if so, you may have a bad stator, when it warms up, it expands, and may have a broken wire that pulls apart and kills voltage to your coil/ignition system. I had a problem on my 95 Wolverine (same engine) where it would sputter on the top end, dealer had to adjust the gap on the sensor that saw flywheel rotations to fire the coil, but yours sounds like an open wire killing the motor entirely.If it starts up later after it cools, I would be looking at the stator.

you might also consider checking the compression

I would think low compression would cause hard starting,and low power/smoking during running. Running till warmed up, cutting out,then stalling and no start until cooled off points more toward an electrical problem, either internal, like the stator, or external, like the cdi or the coil opening up when hot.

Sounds to me like a faulty gas tank/cap vent. If air cannot get into the tank to relieve the volume of fuel being used then a negative pressure/vacuum builds in the fuel tank after a few minutes of riding and then the engine will begin to starve or run lean, get hot, and finally stall. The time it takes the engine to cool could also be the time needed for the fuel tank to levelize so when you start it after it has sat for awhile it will run well until it leans out again and the cycle continues. Try running without the gas cap or better yet with the gas cap but just barely on. If it runs fine and does not stall then you know the fuel tank vent hose is or some other hose is clogged.

This time of year, I would think we would be looking at a pressure build up, not a vacuum in the tank, gas vapor expands at an extrodinary rate, especially in summer, last week I took my Grizzly out for a 60 mile ride, ran it almost empty, it had a bad vent valve, it had so much pressure built up in the tank,it nearly blew the cap out of my hand. Funny thing was, it ran fine all day like that. In the winter, with cold temps, I have had my snowmobile run crappy after several miles, and found a vent hose pinched, making a vacuum in the tank from the fuel being used, because at 12 degrees, no vapor expansion going on there. I'm still voting for electrical problem, they are notorious for temperature sensitivity.

I've had the same problem for two years. When it gets hot (running temp), my 2005 Polaris 700 EFI sportsman starts misfiring and loosing power. Eventually it stalls out as if its not getting fuel. I've gone through the entire fuel system twice. Replaced the fuel pump, fuel filter, flushed the fuel tank, new injectors, new "dry" air filter, checked / cleared fuel vents and cap, and yes new spark plugs.
It's got to be the coil or some component of the EFI (electronic fuel injection).

Suggestions please???
11/04/2012

Welcome! Most of the problems on Polaris efi systems was the sensor wiring harness failures,not the sensors themselves! Erratic problems: Would run good for awhile,then would spit, cough,not idle, would die,etc. Look in the Polaris expert section under the "sticky" post on 700 efi problems. This applies to 500,700,800 efi models. Repair kits are available,Polaris kits(NOT recommended) or heavier wire aftermarket kits for the t-bap(map sensor) or tps sensor wiring. You can visually trace the wires from the sensors on the throttle body down into the harness. Usually you can either find a bare wire or a wire that feels soft(internal breakage) Plus on the 700 trace the wires from the crank sensor harness that wrap underneath against the starter motor. I've found bare wires here also that caused problems when they touch the starter or engine case. All future questions will be seen more under the Polaris section on your 700 than in the Yamaha section. OPT