@#!! vapor lock %*!

[jrt]

Or as Cap'n Haddock would say- Thundering herd of zapotecs!

Finally met Mr Vapor Lock yesterday and here's my impressions:

It sucked. Or blew...take your pick.

It resulted from riding my bike around town- 2 miles here, 2 miles there, just shopping with my wife for plants and stuff (yes, plants...no not that kind ) on a warm day. The oil temperature in the sump was registering about 100 °C. I think it happened because I got the motor good and hot, then let it set and the heat rises to either the pump or the filter. There wasn't much wind for cooling. I was also low on gas, so I wonder if that contributed to it. After 30 minutes it was cured, the oil was down to 80 °C, but it was an aggravating 30 minutes.

So now I have to figure out what Al did as far as his space age fittings and whatnot. Or I might look into relocating the pump. It looks like there's enough room to put the pump and the filter on top of the spine and use 1/2 or 3/4 inch of hose to connect them (lot less plumbing that way). Also, I was wondering about putting a heat shield on the bottom of the spine- a rectangle of plastic or something- but I also wonder if maybe that would trap heat between the deflector and the gas tank, instead of just deflect it.

Or, take a cue from Steve, and plumb in a T fitting at the return hose with a valve on it to bleed off the pressure? That sounds safe.

J

[Guest Nogbad]

I wouldn't have thought the problem could be solved by bleeding the vapour off from the return side. The vapour will arise most enthusiastically on the suction side of the pump. If the NPSH (net positive suction head) at the pump inlet is lower than the vapour pressure of the fluid at the temperature of interest, the inlet of the pump will cavitate and produce vapour lock. Hence, as the NPSH is proportional to the level of fuel in the gas tank above the pump, the fact that you were low on gas could well have been a problem. Also, the less gas in the tank, the less heat capacity to absorb the heat rising from the engine so the fuel would get hotter quicker. The one time last summer when mine did it, I also was low on gas.

 

I have decided to live with mine as it is, and see if it recurs often enough to merit fiddling about.

[fernando]

it happened to me about 4 times 2 years ago.

 

always in miami and always when just filled up the tank.

 

has never happened in the northeast

 

 

fernando