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Discussion Starter #1
Does anyone know what the orange filler neck that hangs down into the tank actually does? It appears to prevent the complete filling of the tank.

This is the first (only) bike I have seen that has one.

Has anyone removed the gas cap assembly and cut down the filler tube?
 

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Probably to allow room for expansion as gas heats in summer.
 

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Clem has it right. You can fill to the top of the tube by lifting the gas pump nozzle and adding slowly at the end. If you overfill the excess will run out under the bike. I routinely fill to the top when I am about to ride for a significant distance that will burn off enough fuel to allow for expansion when I stop. Not much of a problem in cold weather.
 

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If you overfill the excess will run out under the bike. .
If your bike is here in North America then it will not just flow under the bike, it will flood the charcoal filter that North American bikes have and it can destroy that filter.

I'd suggest not over filling it past the fuel filler neck. It is probably not much more fuel anyway, unless as Las pointed out, if you're going to be riding far enough it will result in the fuel level dropping below the fuel filler neck.
 

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I've found that the tank holds more gas than BMW claims it does. I always figured the filler neck was a splash guard provision.?
 

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Evaporative emissions control or EEC. It leaves a space for the bike vent system. The manual says fill to the bottom of the neck. If I do, the tank holds 5.3 gallons. If I cram all I can in the tank, it holds 6 gallons from bone dry.

I took that neck out once. There is a vent valve that is only open when the bike is level. Tip the bike and it closes. There is also a water drain from around the filler to the ground.

The system keeps Hydrocarbons out of the air.

David
 

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Evaporative emissions control or EEC. It leaves a space for the bike vent system. The manual says fill to the bottom of the neck. If I do, the tank holds 5.3 gallons. If I cram all I can in the tank, it holds 6 gallons from bone dry.

I took that neck out once. There is a vent valve that is only open when the bike is level. Tip the bike and it closes. There is also a water drain from around the filler to the ground.

The system keeps Hydrocarbons out of the air.

David
My vent valve must be stuck open...'cause if my tank is full (or even near full), and placed on side stand, my lower vent tube will copiously produce raw gas. This phenomenon is primarily a summer event, which I attributed to simple fuel expansion. I thought this overflow mechanism very un-BMW like Do others witness the same leakage? I'm glad I don't smoke :confused:
 

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IF I overfill the tank and leave it on the side stand in the hot sun, I get a puddle under the bike. Last time this happened, I was still at the gas station. Filled the bike, parked near the store entrance and went inside to pay. When I came out there was some gas under the bike. The guy filling the tanks at the station said "your float is sticking" I smiled. Floats are in carburetors. I think he knew that and was joking.

With the bike on the side stand, the vent is closed. There is a weight that hangs down and is only open when the bike is level. I think the gas pushed out under the cap and drains out the water drain in the cap area. Look at a parts picture to see what the heck I am talking about. I think it sort of like a rollover valve in a car.

There are 2 vents one below the cap sealing area with the weight and one above the cap sealing area to drain away water (or excess gas).

David
 

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Discussion Starter #10
Ok, so if I am reading everything correctly, I should be able to remove the evap system and then remove the orange tube. That will allow me to fill the tank with 1+ more gallons. The only issue might be overflow if I fill the tank to the very top and leave the bike on the side stand.

I removed the evap system on my 2009 Moto Guzzi V7 Classic and saw an immediate improvement in the way the engine runs. I was also able to lower the idle rpms by a couple of hundred. The popping on deceleration also went away. On the Guzzi the output hose from the evap canister fed into the intake track after the throttle bodies. I think that messed up the fuel/air ratio a tad and also did not help to keep the throttle bodies in balance.

I doubt that removing the evap system will affect the engine of the R12R. I would just like to get a little more gas in the tank. I have a 2-3k trip planned this year and a cross country ride planned for next year.
 
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