[High On Octane]

So, regular day at work today.  Until about 4pm when a customer comes in that bought a 2010 Heritage Softail Classic some months back.  Needs a battery because he had to jump his bike twice today.  Cool, got you covered!  Can you install it?  Sure, no problem.  Additional half hour of labor.  Sounds good, let's do it!  Bike is outside running,

My only tech was tied up in a complicated carb job, so I tackled it myself.  Tested the charging system, and everything was good, battery tested bad.  Just another day in the shop.  Get the old battery out and go help a customer get checked in for a dirt tire drop off.  Come back out and my tech tells me "I heard a weird noise coming from the bike and looked over and there was fuel coming out of the overflow vent on the tank.  So I opened the gas cap and it was pressurized and sprayed out."  Weird, but ok.  Get the battery installed, bike cranks but won't run more than a second.  Open the gas cap and it sprayed out again after just a couple of minutes.  Listen closer.....  The last gallon of fuel is BOILING inside of the tank and vaporizing out!  The only thing we could think of to do was put a couple of gallons of fresh fuel in, which cooled the tank and fuel down, and then it fired right up.  But, talk about an interesting end to the day.

[longstrokeclassic]

Not just a Harley!

The old Triumphs used on escort duty for The Royal Household Calvary  occasionally suffered the same issue with boiling fuel. Perhaps having a large hole in the petrol filler caps helped alleviate potential running problems  

[Richard230]

Sounds just like a 1980's BMW K100RS to me.    I was told that "they all do that, sir." 

[Vince]

     It can happen to any bike with an inadequate or plugged vent. The problem should be addressed now. Depending on the cap you may be able to unplug the vent or drill the vent a little bigger, or you may need to replace the cap.
     If you ride in a very hot area in city traffic you may benefit from a layer of insulation on the underside of the gas tank.