A Look at the Fuel Tank Vent Valves in the Fuel Filler Plate

While the XR1200 may be the best handling motorcycle that Harley Davidson has made recently, there are still several aftermarket upgrades to improve its suspension and handling.  Shock absorber and front fork upgrades are common among XR riders.  Until a few weeks ago I had overlooked one of the most dramatic and cost effective handling upgrades that can be made to the XR1200 installing solid rear motor mount/swing arm bushings.

 


The Buell Fuell Tank Vent Valve Recall 

Fuel tank vents on earlier  Buell motorcycles have been replaced under recall in the past.  The Fuel Tank Vent Valve on Buell motorcycles was redesigned in 1999, and a retrofit was made available to 1995-1998 Buell motorcycles under Buell Safety Recall Bulletin 0815 (B-022).  According to the Buell Bulletin, "Certain 1995 through 1998 models are equipped with vent valve assemblies which can prevent sufficient fuel flow which may cause the engine to stall or misfire. In addition, under certain conditions, the vent valve can cause the carburetor to overflow which could result in fire and death or serious injury."  This was remedied with Buell Vent Valve Installation Kit (Part Number 91432-96Y). which updated an older internal vent valve using check balls and exiting through a straight through external vent tube fitting, with a newer and larger internal tank vent valve that exited through a 90 degree hose fitting (Buell Part 93923Y). 

As a part of this safety recall the Buell kit has a safety decal that states:

"Install the fuel fill warning decal provided in Vent Valve Kit to the fuel tank.  Note:  Decal indicates that fuel tank should not be filled above 1 inch (25.4 mm) below bottom of the filler neck insert."
There are a couple things to consider when thinking about comparing this earlier Buell recall to the XR fuel tank vent valve system.  First, the Buell and the XR vent valve systems are designed entirely differently.  Next, the Buell safety recall was related to the vent valve not allowing air into the fuel tank and causing a vacuum that starved fuel flow to the engine.  Concerns about the XR vent system relate to the possibility that the fuel tank may not be allowing air to escape, causing the tank to pressurize under some conditions and contribute to fuel tank swelling.
 

The XR1200/XR1200X Fuel Tank Vent Valve System

The XR1200 fuel tank is a black plastic tank under a painted tank cover.  The Fuel Filler is located in the top of the tank, centered toward the front of the bike as shown below.  I am not going to go through fuel tank removal here, but to take a look at the Fuel Filler Plate and the the fuel tank vent valve system the cover does need to come off of the tank.


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XR1200 Fuel Filler Plate
 


The following is a picture of the Fuel Tank with its decorative plastic cover removed  Under the cover one can see the fuel tank ground wire and the tank overflow vent tube.  To remove the Fuel Tank FIller Plate both of these need to be unplugged.  (Note that in the following picture I am unscrewing the mounting screws for the air box to remove the tank.  These screws do not need to be removed to examine the Fuel Filler Plate and the tank vent valves.)


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Fuel Tank Uncovered



NOTE:  The Fuel Filler Plate is sealed against the Fuel Tank with a large o-ring gasket.  This o-ring absorbs fuel and will swell.  Because of this swelling it is is highly unlikely that this o-ring can be reinserted in the groove in the tank and reused for re-installation of the Fuel Filler Plate on the tank.  Therefore before removing the Fuel Filler Plate it is advisable to have a new o-ring (HD Part # 11570) on hand.



Six Torx screws hold the Fuel Tank Filler Plate in place on the top of the gas tank, as shown in the following picture.  Once these screws are removed the Fuel Tank Filler Plate can be lifted and removed from the tank.  In the below picture I have circled the tank vent valve in the top right of the picture.  This is one of the three valves for the fuel tank.  This particular valve passes straight through into the fuel tank.  It works independently of the other two tank valves, to allow air to flow in to the tank if needed, to prevent a tank vacuum.  Without this valve it could be possible for a full fuel tank to build a vacuum as the motor draws fuel, affecting the ability of the fuel pump to push fuel to the injectors and possibly causing the motor to stall.  (This would be a comparable situation to the reason for the Buell vent valve recall.)



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Fuel Filler


The overflow tube connects to the port shown in the lower right of the above photo.  It can be pulled off of the overflow port to remove the Fuel Tank Filler Plate.  Shown, but not marked, at the lower left of the Fuel Filler Plate is the ground wire.  It can be pulled straight up and off its mounting stud for disassembly.


With the overflow tube, ground wire and six mounting screws removed, the Fuel Tank Filler Plate can be removed.

Below is a picture of the Fuel Tank Filler Plate turned upside down to show the three tank valves that pass through it.  The white tank valve to the left of center is the bottom of the vent valve shown in the above picture.  As mentioned, it functions independently of the other two valves.



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Back of Filler Plate Showing Vent Tubes


The two other valves shown in the above picture work together to allow the fuel tank to vent excess pressure.  They are connected together and flow out of the overflow tube port on the outside of the plate. 

The taller tube to the right has an internal float valve.  This valve allows the tank to breathe freely when the level of fuel is below the height of the float.  For this vent to open, the level of fuel in the tank must be nominally 1" below the restrictor plate in the filler neck that prevents leaded fuel nozzles from being inserted in the tank.  If the fuel level in the tank is at least 1" below the restrictor plate, this valve will not allow air to pressurize in the fuel tank.  As a safety precaution, the float in this valve will also close if the motorcycle tips, preventing fuel from accidentally draining out of the overflow tube in an accident.

The shorter middle valve only comes into play when the tank is filled completely, i.e. above the last 1" of the top of the tank.   This valve will allow pressurized air/fuel to escape from the tank when the tank is completely full.



Function Checking the XR1200/XR1200X Fuel Tank Vent Valve System

Harley Davidson does not publish specifications for the pressures at which the valves should function in the Fuel Tank Filler Plate.  There are however, a couple of easy function checks that can be performed to determine whether the vents are operating properly.


The first thing to check is the single vent valve that allows air to enter the tank.  This valve should be checked before removing the Fuel Tank Filler Plate, on a fully assembled tank with the fuel tank filler cap in place.  To check this valve a hand vacuum pump is attached to the overflow tube port, as shown in the below picture.  If the pump is operated, the vent valve should allow air to flow into the fuel tank and the tank should not build a vacuum.  If the tank does build a vacuum the vent valve is bad and the Fuel Filler Plate should be replaced.  Note that this problem would be the equivalent of the problem that caused the Buell vent valve recall, and could cause the motorcycle to stall with a full tank of gas.




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Vacuum Pump on Filler Plate - Vent Valve Uncovered


Next, perform the same check with the vacuum pump while securely covering the vent valve port with a finger.  An empty tank may take several pump strokes, but the tank should build a vacuum.  If the vent valve is securely covered and the hose connections are good, the tank should build about 25 in-Hg of vacuum.  If the tank will not build a vacuum then it likely has a leak and should be checked.  First the filler cap should be checked to make sure that it is securely closed, and that its o-ring (HD Part # 61573-08A) are in good condition.  Before proceeding on to the next operational checks any leaks in the tank should be identified and fixed, as the fuel filler cap and its o-ring must be in good condition for the next checks.


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Vacuum Pump on Filler Plate - Vent Valve Covered


Just for reference, the next picture shows covering the tank vent valve from a different angle.  This picture is just to show the connection to the overflow port, the location of the  vent port, and the edge of the fuel filler cap o-ring.  This operational check will not work with the Fuel Tank Filler Plate off the bike like this.



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Fuel Tank Filler Plate


Next, the function of the connected pair of pressure relief valves is checked.  To perform this check, the Fuel Tank Filler Port must be removed from the fuel tank.

With the plate removed and the fuel filler cap installed in it, the vacuum pump is connected to the overflow tube port.  The plate is turned upside down and with a thumb covering the middle pressure valve, and the pump is operated to attempt to build a vacuum.  With the plate in this upside down position, the float valve in the tall tube should fall down and close its breather port.  This should allow you to build approximately 15 in-HG of vacuum.  Higher vacuum levels are ok, as they would show that the float valve is closing more securely.  However, if a vacuum can not be built with the plate inverted, it means that the safety float is not functioning properly and might not prevent fuel from leaking from the tank in an accident.  If needed, the tall float valve port can be disassembled and cleaned by carefully picking the locking tabs in the end cap.



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Testing Pressure Relief Port


If the filler plate does build vacuum in the previous test, the same check is repeated without a thumb on the middle pressure relief valve.  In this case the float valve will be in its closed position and the vacuum pump should pull air through the middle pressure relief valve.  To prevent fuel from draining from the motorcycle in an accident, this port should normally be closed and require some vacuum to open.  While there is not a published HD spec for the pressure at which this port should open, functionally, it should open with about 2-5 in-HG  (which is less than 2.5 psi of air pressure).

If this valve does not open at low pressure, there is a danger of air pressure building in the fuel tank when it is completely full, and for safety purposes the Fuel Tank Filler Plate should be replaced.  Note though, that this valve only comes into play when the fuel tank is filled to within the top 1" of its capacity.  The fuel tank should never pressurize i a partial tank of fuel, if the adjacent tall pressure valve is working properly.




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Testing Pressure Relief Port


Just a reminder - the Fuel Tank Filler Plate o-ring (approximately 12 cm in diameter) shown in the below picture, seals the Fuel Tank Filler Plate to the fuel tank.  This o-ring does absorb fuel, will expand, and will likely not be reusable during re-installation.  A replacement o-ring should be purchased before disassembling the fuel tank.


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Fuel Tank Filler Plate O-ring



Conclusion

The fuel tank vent valve system in the XR1200 is a fairly sophisticated design that is different from earlier Buell and Harley motorcycles.  The redundant design of the pressure relief ports makes it unlikely that the fuel tank will pressurize, unless the middle pressure port discussed above should fail in a closed position and the motorcycle is stored in a hot environment with the fuel tank filled to within the last 1" of the top of the tank.  One person has reported that his fuel tank was tested and this center pressure relief port was found to open at an excessively high pressure - but I have not personally observed this situation.  In general though, it is not likely that the design of this vent system will allow pressure to build in an XR1200 fuel tank, or that the vent valve system will allow sustained fuel tank pressurization that would contribute to the problem with XR1200 fuel tank swelling that some individuals have experienced.


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