Brute force 650 4X4 carb

[Dark_ale]

I have let my Brute force set up for a couple of months and I went out yesterday to start it. It started right up after a few try's but would not maintaine idle even after warmed up.
So I took it out to ride and it runs great, but when you come to a stop it wont keep running.
Also when you really get down on it, about 50MPH it will back fire.

If you put the choke on just a bit it will idle, so its not getting enough gas right?

[RCW]

It sounds like the carburetors have become partially gummed from old gas, and will need to be disassembled, cleaned, and inspected.

If you do not have the repair manual do not attempt this, as they are set-up and jetted differently for the right and left carbs, and require care to make sure each jet and passage is cleaned and reinstalled properly. You also want to follow the documented test procedures for the vacuum valve diaphragm that lifts the jet needle, as they also tend to get damaged if they are a couple years old and are disassembled, and they are about a $100 each to replace.

Also examine the air cut valve on each carburetor carefully for any cracks in the diaphragm and to be sure the seal O-ring has not started to melt from old fuel. The function of the air cut valve is to shut off the fuel at idle when you shut down the engine, so if it starts leaking

The Brute Force also has a fuel pump, so it may well be contaminated with a coating of crud on the valves from the fuel going bad. That is likely what is causing the lean condition at higher speed. A good fuel conditioner/cleaner/restorer such as PRI-G will clean that up as long as it has old fuel has not started distorting the internal components.

Your fuel filter likely has started to plug too.

The oxygenated (contains ethanol alcohol) fuels that are pretty much everywhere anymore start going bad in about two weeks and begin to separate and form gum in less than a month. So if you are going to let your ATV set for more than a week with fuel I strongly recommend using a fuel stabilizer that is designed for alcohol fuels.

Around our area we have identified a wholesale oil distributor that still sells bulk regular unleaded for off road and marine use only, and now buy our gasoline from them. Some airports and marinas will also sell non-oxygenated fuels to the general public. The difficulty is transport if you do not have a pick-up and a real fuel tank, as all gasoline is extremely dangerous to carry in a jerry can in the car trunk because of the high levels of cancer causing volatiles they now contain evaporate easily and can explode with just a spark. So, it is much safer to just buy a jug of PRI-G and add a bit to each tank of filling station gasoline.