Fuel tank vent question

[montmil]

My R65 still has an occasional venting problem. The issue manifests itself when the fuel stops flowing to the carbs!

Note the photo and the vent location. I have run a double-length pipe cleaner into the pipe and did not feel any obstruction but I don't know where the vent ends. The tank is full of fuel and I don't wish to remove the heavy tank in this condition... I might ding it.

The question is, "Where does the vent "vent"? I'm wondering if some debris or an insect has found a new home.

[Justin B.]

This is more of an overflow tube and it terminates on the underneath, left-hand side in about a 1/2" (or so" "nipple".  I have seen a hose at6tached to the nipple on some and none on others.  As far as the actual tank venting I believe that is all in the cap.

[nhmaf]

Justin is right - the venting is primarily in the cap body, which screws in and pushes against the inner ring, or "neck" of your fuel fill hole.   Depending on how tight
the top of the cap and the plastic ring push against the tank (can be compounded by trapped water and tank bags) it may not vent to the atmosphere very well and
the fuel overflow (if unobstructed) may help  with the venting.   I've been running mine without any overflow hose for quite a while, but recently put some 1/4"  or 3/8" tygon
tubing from the overflow nipple on the underside of the tank and ran it back to the battery box and down a frame tube - I have been filling the tank a little more fully
these days in the interest of getting the most miles out of each fillup, and decided that I didn't want to end up dumping gasoline down in to the alternator/starter if
it accidentally spilled over.

It is possible that the overflow tube does help a bit with venting, especially when you have such hot days and have recently put some cold gasoline into the tank.   You could probably try some 14 gauge wire or something a bit stiffer than a pipe cleaner to run down through to clear an obstruction if the pipe cleaner isn't working.   The bottom of the tube is on the left hand side of the tank, underneath, in the front half of the tank toward the frame backbone.

[montmil]

Hummm...  OK, will check this out further. In the times I've removed the tank, done never looked underneath. Have a new fuel cap. Got rid of the nasty looking one with the epoxied-shut keyhole. I can get fuel flowing by a little turn of the cap. But then the neat flip-up handle isn't square to the tank. A bit too anal retentive, eh?

[DgM]

Reads like your gas cap is still not venting.  When using tank bag on my 1983 R65 I was experiencing venting/carb overflow issue and needed solution.  I cut a circular hole in tank bag pad over gas cap, had a friend cut a piece of 1" pvc pipe lengthwise (halfpipe), placed pipe open side down from gas cap to just beyond front of tank bag pad, between tank bag and pad, one end over hole over gas cap.  Success.  160 mile weekend ride with no venting issues.

[donbmw]

From personal experince you need to run a hose for the overflow tube on the fuel tank. My R90 did not have a hose and one day I filled the tank had some fuel drain out the overflow. When I turned the key and hit the start button I had this fuel catch on fire. Lucky we got it out without any damage.

Don

[Bob_Roller]

I had not quite as bad of an experience that Don had, but after a 3 hour ride at highway speeds, I refueled, and got quite a bit of overflow, and it ran onto a very hot engine.

I was enveloped in a cloud of vaporized fuel, I wisely pushed the bike off to the side to allow the fuel to evaporate before starting.

Ever since then, I have had a piece of clear tubing attached the the nipple on the bottom of the tank, so the overflow gets routed to the ground, and avoids contact with the engine.

Don, I bet that was a bit exciting to watch your bike catch fire!!!!!

[donbmw]

I had not quite as bad of an experience that Don had, but after a 3 hour ride at highway speeds, I refueled, and got quite a bit of overflow, and it ran onto a very hot engine.

I was enveloped in a cloud of vaporized fuel, I wisely pushed the bike off to the side to allow the fuel to evaporate before starting.

Ever since then, I have had a piece of clear tubing attached the the nipple on the bottom of the tank, so the overflow gets routed to the ground, and avoids contact with the engine.

Don, I bet that was a bit exciting to watch your bike catch fire!!!!!

I was setting on it when this happen. Talk about a hot seat'!!!

Don

[Rob Valdez 79 R65]

Mine still has the original black rubber hose.  I don't know if it has ever been needed or not.

[Justin B.]

I think Barbara's '84 is the only bike we have that has the hose.  Sounds like it might be a good thing to do someday as I'm also starting to "pack" the tank...

[MrRiden]

I was puzzled by that "overflow" fitting when I first got the bike as there was no tube. Did up a clear vinyl one and no problems. All Venting is done through the cap and ditto to all the above. Don, you may be the only R65 rider I know of who had a real Toaster Tank!  
rich

[nhmaf]

Ha !  That was a VERY funny pun, MrRiden !

I'm very glad to hear that neither you nor the bike was hurt, Don !

Gasoline vapor can be very touchy stuff - I once unintentionally "napalmed" my entire back yard and
had 2nd+ degree burns on my feet a few years ago - I'm not listening to my younger brother's advice about
flammable liquids anymore...

[Semper Gumby]

I run the overflow tube down the front side of the LH cylinder .  Regularely see some Fluid venting from around the key on my locking cap...Is there a cap that I can vent some where else???

TTFN,

[R80rider]

Interesting enough, I had a BMW dealership mechanic tell me to check the vent hose on the bottom of the tank when I was having intermittant stalling problems.  he claimed if the hose was pinched it could interrupt fuel flow.

This, of course, sounds to be in direct conflict with the information provided here.

By the way, there was no hose attached to the outlet on the bottom of the tank so I have no emprical data to share, but thought I would throw this out there.

[R80rider]

Here is an interesting article from http://home.jps.net/~snowbum/locks_caps_etc.htm

about fuel cap venting.  

As my cycle stalled twice today even with the cap off my other cycle, I am thinking of modifying the original cap with the silicon per the recommendations here, but wanted to see if anyone had tried this and what the results were?

By the way, I purchased pipe cleaner and ran it down from the venting (overflow) hole in the gas cap well until it came out the venting outlet where the hose should attach in the bottom of the tank and it was clean and unobstructed.

Bill

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VENTING:  
The late 1977 (or perhaps from 1978) gas caps are changed in design, so that they allow air to pass to the inside of the tank, but fumes are not supposed to pass to the outside of the tank.    To accomplish this, their are valves built into the cap.  The very first of these caps could have problems.   The symptom of a venting problem is when the bike starts running very lean, may buck and seem to run out of fuel, and this typically happens after some time on the highway, the time can be shorter if the tank was rather full to start with.  OPENING the cap (unscrewing it a bit) will 'fix' the problem within 15 seconds, and this 'test' is nearly 100% for a bad cap vent.   The cap can be modified to fix the problem permanently.  Put it upside down on your workbench.   Drill AWAY from the center, any direction, about 1/2" from the center.  Thus the hole you will drill is off-center.   Drill, 3/32", from the bottom of the cap, through the metal shell, and continue drilling carefully....go through the air space, and drill into the softer material that you then feel you are drilling through....it is maybe 1/8" thick. Drill through it, and then stop drilling.  Clean out the cap as best you can of drilling swarf.   Replace the cap on the tank.  That's all there is to this.