Vapor Lock (Preventive maintenance gone bad)

So far, most maintenance I've done has been oil changes, bolt tightening, checking air in my tires, and giving the StradaVariator a bath now and then With the onset of warm weather I discovered that one of the "preventive maintenance" items I took care of last fall when it was already comparatively cool out, began giving me problems.

I had shortened my fuel lines, which sagged in places, and routed them directly to and from the various compnents in the fuel line, using the shortest possible lengths of hose. This spring I have been experiencing periodic fuel starvation which only began when I was at least .6 or .7 gal low on fuel. My first thought was that the vacuum operated fuel pump was only opening part way, and that with the lower pressure that comes from having less fuel in the tank, it wasn't allowing enough gas to get through, causing the symptoms of running out of gas. It usually happened when I had been running at 2/3 throttle or more.

I replaced the vacuum operated fuel switch with a manual petcock, and the problem seemed to go away for a tankful of gas or more. Then it struck again... under the same partial tank conditions. :o(
Then I began to suspect the oversized automobile fuel filter I had installed in the fall, figuring the element was too heavy, with pores so fine that it really needed fuel pump pressure to push gas through it.

I was about to replace the filter when it happened again and I reached underneath the cowling to make sure the manual petcock was all the way open. I wasn't reaching for quite the right spot, and almost burned myself on a VERY hot frame crossmember. After I let it set for a minute or so, and bounced the scooter up and down a time or two, which seemed to speed up the time it took to get fuel again, I headed home and pulled my underseat storage basket, discovering that the last vertical run of gas line was laying right against the frame piece that got so hot. I never even had given vapor lock a thought, because the last section of fuel line near the hot engine was nearly vertical all the way. I've experienced vapor lock on cars before, and it was always in a nearly horizontal section of fuel line. Apparently on the scooter, the pressure of the fuel in a full tank was enough to push fuel through that hot vertical section of fuel line until the tank was down to half empty. Once the tank got to a certain level, the pressure was no longer sufficient to push gas through the "boiling" section of fuel line, and it would vapor lock. Where I thought that sitting a minute or two was allowing fuel to fill the filter back up, actually the frame was cooling pretty quickly once the engine was off, and then the pressure of the gravity feed system was pushing right through the vapor locked vertical section of fuel line.

Once I re-routed the fuel line so it no longer touches anything near the engine, I have had no further problem during two more tanks full now, part of the time in 90 degree temps, hottest we've had so far this year.