Carburetor Woes

[Gunner]

I have an old (1988) Polaris Trail Boss that was leaking gas from a cracked hose that is attached to the carb. I'm not talking about the fuel line hose to the carb. from the gas tank. I replaced the hose, but I am still having some trouble with it. According to the Polaris technical manual, there is a hose that supplies the gas to the carb. (no problems there) and another that acts as a vent. No other hoses are mentioned or shown in the diagrams. But, there are more hoses than what is shown. One hose runs from the right side of the carb. on the top half of the carb. (looking from the back of the ATV forward), and it connects to a hose on the bottom of the carb via another hose with a "T" fitting. Another hose runs to no where off of this "T" with what looks like a filter on it. The carb. is a Mikuni model VM300SS. A look at Mikuni's web site does not show the additional hoses in the on-line service guide.

Is there any one familiar with this set up that can advise me on the proper way these hoses should be hooked up and what may be causing the fuel to still leak? I really can't afford to spend the outrageous bucks that the Polaris service department charges in my neck of the woods at this time.

Thanks in advance!!!

[Cabin Fever]

I'll go take a look at my sled to see what I can make out. My Polaris snowmobile uses the same carbs. All I know right now is that the hose that comes out of the bottom of the carb is for draining the carb bowl. Each of the three carbs on my sled has one of these "bottom" hoses for draining and they are not connected together via tee fittings. There is a simple plastic plug in the bottom of each one of these hoses that is held in place with a hose clamp.

[moopups]

In the event of your vent being not open to the air, this would mean that the float bowl vent is not allowing the inside air to escape when fuel enters the float chamber. The air inside is compressed until the weight of the fuel equals the compressed airs pressure. In that the air is at the top of the chamber, it presses the fuel down into the feed jet, which forces the fuel up and out into the venturi of the carb makeing it leak out the air intake. If this is where your getting the leak you need to clear the vents clogged escape route.

[Cabin Fever]

I just took a look at my sled....three cylinder, three carborators. The only hoses that connect together with a t-fitting are the 1/2" black fuel lines. The fuel lines come out on the left side of the carbs. On the right side of the carbs is 1/8" clear poly tubing that go to the air intake...these are the carborator bowl vent ports. And the third hose is comes out of the bottom of the carbs. Like I said before, these are drain hoses (1/2" black neoprene) which are plugged. They are used to drain water and sediment out of the carbs.

Another cause for fuel leaks are a weak needle and seat valve in the carb. The gas tank is at a higher elevation than the carb consequently this puts pressure on the needle and seat. If the needle and seat leak, gas will flow out of the carb vent.

[Gunner]

Cabin and Moopups. Thanks for the feedback! The hoses I am talking about are 1/4" clear plastic hoses. I am thinking as you mentioned that they are drain/vent hoses. When I blow on them, air moves through them and the carb. Gas is leaking out of the carb from the bottom hose. So I guess I will have to force fit my fingers into them tight quarters and take the carb off and give it a going over to find out what is causing it to leak. A few drips now and then would be one thing, but a pretty constant drip is no good.

Thanks again, and any other advise would be greatly appreciated!

sounds like you need a new needle and seat or you have a bunch of trash in the carb If it is dripping.
if it is running out floats are stuck or bad but I think that has solid floats so they don't go bad but they are known for sticking. if it is running out tap the bottom of the carb with a screw driver it may stop.
That carb is a breeze to work on just get an overhaul kit you'll need it.

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