Sounds like the tank vent system has something wrong. I had an old two stroker that would infrequently die without warning. After stopping and checking fuel, it would start back up and be good to go. Turns out the tank vent was pinched, creating a vacuum condition in the tank and preventing fuel from flowing. Loosening the cap relieved the vacuum and it would run again. I tried all sorts of things with the vent tubes, but never fully corrected it. - MarkC

 

If the vent tube is good, it may be the heat in the fuel lines. Does it happen when you don't kill the engine. The first time you mentioned a quick break. Was there a stop the 2nd time or did it lose all power mid-ride?
Mine was having the problem of, if it as hot and I stopped for just a minute or two (say take off a jacket or adjust a helmet) and restarted it had no power and died if I applied much throttle. Probably the fuel inthe fuel line, which runs pretty close to the hot front of the engine, was vaporizing and blocking up the fuel line. I put heat wrap on my exhaust and manifold. No problems now. Before that, if I stopped for 10 minutes or more, the machine would have time to cool and there would be no problems.
But I never lost power unless I shut off the engine and tried to restart quickly. Never while the engine was still running. I assume that keeping the fuel moving doesn't give it a chance to stay in the fuel line by the engine long enough to vaporize.

 

Could be the vent line, except when you said you took the cap off the second time and that didn't help. It sounds like it could be a fuel pump issue. I have known of a couple that have had this problem. The fuel pump starts to get hot and won't work properly. Top off the tank with gas and the extra gas cools the pump down and they fire right up. The only real fix is a new fuel pump. One way to check it is to hook up a fuel pressure gauge and secure it where you can see it while riding. Keep an eye on it when you have been working it hard at slower speeds. This is assuming you have a fuel injected machine. I'm not sure what you are riding. With the header pipe coming off the head directly below the tank, there is a huge amount of heat transfered to the tank. At slower speeds there isn't enough air flow to keep the heat from building up under there. Also make sure the silver heat shield is still stuck on the bottom of your tank. They sometimes fall off.

 

+2 with Kicker!! Heat is your problem!

 

If the reflective heat shield is missing off the bottom of your tank that would be a huge problem. Whether the cause is hot fuel, or a hot fuel pump, keeping the tank shieded is the first step to a cure.
I used som eof this stuff on the backsides of my plastics to keep them from melting before I went to wrapping the exhaust. Thermo-Tec : Adhesive Backed Heat Barrier I would work very well on the bottom of the tank as well.
Some people wrap it around their fuel lines as well and hold it place with hose clamps.

I chose to go with heat wrapping the exhaust. If you want to look into that I wrote and exhaustive account of mine on this thread (pun intended) http://www.polarisatvforums.com/for.../forums/atv-repair-maintenance/27702-exhaust-seal-replacement-exhaust-wrap.html Now I can almost touch my header pipe even when I've been riding hard.

 

Great info. I had trouble with this last summer once and was looking for heat shielding recommendations.

 

Vapor lock is a thing of the past. You obviously have a vent tube problem, or a dirty fuel filter. Check both ends of your fuel system. On an atv you would warp your cylinder head before you vapor locked.

 

how far in the past?

 

Keep us updated and let us know what you figure out. This will be good information for others to reference.

 

Vapor lock can happen to anything,still! I had a dredge motor that locked up because of heat. I now exhaust wrap everything.

 

I've had 3 good rides since my exhaust wrap. Long rides with some stops short enough to not allow the fuel lines to cool. Last year I would have "vapor locked"'on all 3 rides. This year: no problem yet. (well, except a wet TPS sensor but that wasn't heat related.)

 

It could vapor lock, but only if the fuel pump isn't putting out enough pressure. I believe these pumps run around 75 psi, so if it is working properly, it will push the fuel to the injectors. I do agree with the rest of you. It is caused by the heat from the headers, but I believe the problem is the pump getting hot. If it is the fuel pump causing the problem, you can buy just the pump. Polaris will try to sell you the whole tank/pump assembly.

 

UPDATE. I replaced the fuel pump (O'Reilly Auto Part # E2002 $80.00), checked the vent tube on the fuel tan, Heat wrapped my exhaust pipe, and installed new heat barrier pad on the bottom of the fuel tank.
Have a 300 mile ride coming next weekend & I will post results.

Thanks to all for the help.

 

If I understand as to what vapor lock is. Is it not when the fuel line runs very close to a heat source like a exhaust system that a vapor forms in the fuel line causing a blockage or called a vapor lock. I really can't see this happening with the materials in which the ATVs use for fuel lines or real high heat source that close to the ATV fuel lines. This use to happen on some of the old cars that used steel fuel lines. I might be wrong on this so if someone knows different I am willing to learn.

 

Yes it is but it has little to do with the type of fuel line. 87 octane fuel boils at about 180 degrees, (about the same as the engine thermostat setting) higher octane or ethanol/methanol added fuels or winter fuels boil at a even lower temp. Stick your hand under that fuel tank when everything is hot. I have burned the inside of my leg in the summer from the hot air coming out of there. When I have the most trouble with vapor lock is in the spring when it warms up and I am still burning winter fuel from my fuel barrel and in the summer when I am spraying pastures at low speed when its hot out. If you stick your finger in the tank when it vapor locks it will be really hot like hot coffee and when I add a gallon of cold fuel it will start and run fine as fast as you dump it in and flush a little hot fuel from the rack. shield the exhaust heat, fuel stays cooler and I don,t have problems. I started adding diesel fuel to my gas to raise the boiling point and add lubrication for my older engines designed for leaded fuel ~5% makes it keep longer too, less evaporation. diesel boils at over 280.

 

I also add a lil diesel, but more like 3%... It does help. Also, He mentioned hearing it starving for air a couple times. The pump would have to re-prime at that point, But if the fuel was hot, as stated earlier, it also boils at a much lower temperature when under vacuum. I'm not sure what the pump in this quad looks like, but if it has an in-tank pre-filter like on cars, it could be filled with vapour from the earlier-boiling fuel, making it extremely hard for the pump to actually get liquid to start primimg and pumping again. Perhaps that's why once adding fuel to it (increasing pressure over the pump) it would help some liquid to get it and reprime quicker? BTW, i only add diesel to hi-test to combat the "leaning out" from the diesel, preventing detonation.