I returned from the MOA rally a wiser rider.  That's a good thing because I have an issue with the tank that has me puzzled.  The cap is wet and has soaked the underside of the tank bag.  At one point on a very hot afternoon, the engine stopped abruptly.  It only returned to life after I opened the cap.  I thereafter was obliged to carry the tank bag behind me - not the optimal spot, for sure. But to return to the point of the engine stopping, if there is inadequate venting of the tank, why would fuel be escaping around the edges of the cap?  Mind you, this only happens when the tank bag is in place over/on the cap. That suggests to me that the seepage around cap and the engine stalling are related.  
By way of background, I should say the cap was apart within the last year for a rebuild.  However, there were plenty of miles ridden post-cap rebuild without incident.  The engine stopping and the weeping/seeping fuel cap are recent wrinkles in my relationship with the Big Red Beast. 
Any ideas, doubts or WAGS?  What's goin' on?  

I was reading yesterday that it's getting fairly hot around your place, have you considered the possibility of a vapor lock due to hot fuel.
One thing I found recently on my new to me K1200GT was that a wasp had taken up residence in the breather thus making vapor escape from the filler cap when pressure built up in the tank. I was getting a faint smell of fuel when I was stopped.

There are two vents in the tank terminating in the lower right side.  One is to drain rainwater that collects around the gas cap.  The other comes from the Burrito just under the gas cap that vents air and fuel overflow should the fuel and tank become hot. If the tube is blocked the only escape path from fuel is from the Burito which means it leaks out the cap.   It's possible the vent tube is blocked in your tank.  Use compressed air to blow out any possible debris.  Ir use a flexible but stiff wire to poke up the tube and dislodge any possible debris.

If you use compressed air to clean the hole make sure the cap is open because I have seen how more than a few lbs of compressed air can reshape a tank, they tend to become a very different shape from the what they were and they don't fit back on the bike.

Hi I replaced both pipes on mine just to be sure 

I pulled my fuel tank and checked the hoses that connect to the underside.  Both are clear.  The hose that connects to the pipe nearer the forward end of the tank has a valve more or less in the middle, and the other end attaches to a fitting on the crankcase. Is this connection correct? I don't really understand why it should be connected there....  I separated the valve from the hose and found that I could blow through it.  It has a very narrow opening, so it cannot pass a high volume of air,  but it seems sufficient for venting the fuel tank.  
Perhaps I'm over-filling the tank?  I estimate that I leave about 1 1/2 inches of air between the surface of the fuel and the filler opening.  Could that be too little?  This seems unlikely, as I've filled loads of tanks to roughly the same level without issues.  I'm tempted to pull the hose off the sump fitting and instead route it down and back to the rear of the bike.  With the valve in the hose there seems to be no possibility that contamination would find it's way up the hose and into the fuel tank.  Alternatively, I could resign myself to touring without a tank bag, as the cap doesn't "leak" when there is no bag resting on it.  I'm not keen on that as I find tank bags to be very convenient. 
Otherwise, I'm out of ideas.
I was unable to find a burrito in the tank.

Accepting that the cap is without fault, maybe the weight of the bag and pressure from the rider leaning on it IS the cause of the problem. As a simple test make a ring from firm rubber or some such about 3cm thick that fits round the cap fix to tankbag with double sided tape. The idea is to remove pressure from tank cap. Just thinking outside the box.

moriarti wrote:Accepting that the cap is without fault, maybe the weight of the bag and pressure from the rider leaning on it IS the cause of the problem. As a simple test make a ring from firm rubber or some such about 3cm thick that fits round the cap fix to tankbag with double sided tape. The idea is to remove pressure from tank cap. Just thinking outside the box.

The OEM tank bag does not sit on the cap itself to prevent this very problem. The very thick base part stays in place on the tank for refuelling and has a hole in it to open the cap.

Using a different tank bag sitting directly on the cap is going to depress the cap and possibly flex and intermittently break the seal.

The cap does NOT vent the tank at all, the internal pipe vent does it. I have and do inverted the tanks if I have them off the bikes and they don't leak through the cap on me.

brickrider2 wrote:With the valve in the hose there seems to be no possibility that contamination would find it's way up the hose and into the fuel tank.  
 
I was unable to find a burrito in the tank.

Your valve-in-the-hose theory is right on the money except if the valve fails—which it does.   The valve/hose setup leading to the crankcase was developed to meet California emissions standards but can cause excess pressure problems in fuel tanks. There is a service bulletin explaining the condition. Part of the remedy is removing the valve and routing the hose as you have described. The other part is blocking the crankcase port. A short hose fitted to that port then doubled and zip-tied will do the trick.

The buritto is difficult to find unless a mirror and flashlight is used or you have stalked eyes like a lobster. It's fastened to the tank's ceiling just forward of the fuel tank opening.

Describe what you mean by the word "Burito (Burrito)"  please.
Shep

Forward and just under the gas cap is an aluminium cylinder with crimped ends, used to handle fuel overflow. Its shape reminds you of a burrito. Therefore, it has that nickname.

Thank you.
I now have a better idea of what I am looking for.
Shep

Using my dental mirror I was able to see that in my tank.  It's  purpose eludes me. Be that as it may, peering through the port reminded me again of what a complex fuel tank K-bikes have.  There are a lot of complicated bits within.

I'd attach a dry hose to the barb for the fuel return hose and blow air in to feel or hear if it comes out the vent hose near the right foot peg plate. 

I think of the burrito as a cavity for the tank vent pipe to minimise the pipe scooping up sloshed fuel. It has a hole on top to minimise pressure differences inside and outside the tank, and a hole in the bottom so that any fuel sloshed in can drain out.