Fuel Starvation? Or vapor lock?

[AFMO]

Here's my scenario:  My GS left me stranded at 80 mph on the highway once this summer, coughed and sputtered like there was no gas (I had filled up 50 miles before) and died.  Luckily I was able to safely get off the road, load it in the truck and go home.  I assumed this was the well-documented petcock issue, but never got around to fixing it as I was mostly riding around town where high rpm was not an issue.  Last weekend, I took it on a 500 mile trip to northern Michigan, with most all of it being on the highway.  I babied it for the first 100 miles, but found it unnecessary, and it ran extremely well for the whole trip at 75-80 all day.  It was much warmer when it died in the summer, and no more than 60-65 degrees last weekend.  Any idea why it died in warmer weather?  I can't imagine it being the petcock after 500 trouble free, high-rpm miles. 

Also, over the trip, I noticed that after 100 miles of continuous running, my tach would start to wave up and down 1500 rpm or so.  There was no change in engine speed, just the tach bobbing.  Seemed odd, but I guess the cable could be bad.  Any experience with this?

[MacV]

It happened to me today!  Seems to be an identical problem, hot as hell today (100+) was riding for a about a half hour and it just died around 60mph. Sputtered and coughed a bit then stalled out. Got it started again made it a few miles and it died again.  Had it towed home started checking for spark and fuel, everything looked ok and now it runs great.

[bigfatcat]

The ignition control unit (ICU) can give problems once it becomes heat soaked ... the electronics are encased solidly in rubber epoxy and although they provided two large heat sinks, there is absolutely no airflow.

I have an ICU that does this, and another that goes all day long with no problems. So, luck of the draw.

[cbrfxr67]

My bike has a similar problem.  I use a mechanical fuel pump and (dumb) I mounted it behind the engine.  When I ride in our fun Houston traffic at 100 degree heat, it'll start loping and I know it'll stall if I don't get moving.  I think it is a vapor lock issue as the lines and pump are getting cooked.  (Not talking about the GS, talking about vapor lock here.)  After it cools down, idles and runs just like it should.  

[ben2go]

Here's my scenario:  My GS left me stranded at 80 mph on the highway once this summer, coughed and sputtered like there was no gas (I had filled up 50 miles before) and died.  Luckily I was able to safely get off the road, load it in the truck and go home.  I assumed this was the well-documented petcock issue, but never got around to fixing it as I was mostly riding around town where high rpm was not an issue.  Last weekend, I took it on a 500 mile trip to northern Michigan, with most all of it being on the highway.  I babied it for the first 100 miles, but found it unnecessary, and it ran extremely well for the whole trip at 75-80 all day.  It was much warmer when it died in the summer, and no more than 60-65 degrees last weekend.  Any idea why it died in warmer weather?  I can't imagine it being the petcock after 500 trouble free, high-rpm miles. 

Also, over the trip, I noticed that after 100 miles of continuous running, my tach would start to wave up and down 1500 rpm or so.  There was no change in engine speed, just the tach bobbing.  Seemed odd, but I guess the cable could be bad.  Any experience with this?

Two issues that cause this the most,in my experience,are a plugged fuel cap vent and/or a bad petcock.I want to add that it is my understanding that CA bikes do vent through the fuel cap to prevent vacuum lock in the tank.This is done by way of a check valve.I am still not clear where it's at.It could be in the fuel cap or in the emissions equipment attached to the fuel tank or lines.I have a write up on cleaning the non CA fuel caps in the FAQ.Even knowing this,I agree with bigfatcat about the possibility of it being the CDI or ignition triggers/pick ups.That is one of those replace and hope items.It's extremely hard to diagnose an intermittent problem.I start with the most common issue and work back to the least.