Spectuacular Fuel Vapourisation issues

1396midget

Well-Known Member
Hi all

Had a bit of the old stutter and die twice yesterday - first after stopping in a petrol station to fill up, then later in traffic.

I've got an electric pump in the back pushing through the mechanical one so thought that this would have fixed it; and I've not had a problem since I fitted it.

Popping the bonnet in the petrol station (actually just ouside - well done car..) I could see the fuel boiling in the pre-carb filter....

Fortunately sitting for about 1.5 mins with the electric pump on until the float bowls were cool to the touch solved it, both times, but it's a bit odd.

Only change is that it had Esso 97 fuel in it, then just filled up with Tesco 99. Does lower octane fuel boil easier?
 
lower octane fuel is more likely to contain ethanol...

some smaller petrol stations don't use much super unleaded so you may find it's just that it's a summer/winter blend of fuel?

What needles/carbs are you running?

Have you blown through all the fuel lines with a compressor? That can cause expansion as it passes through the pipe... (Expansion, lower pressure, lowers boiling point).

Do you have insulation round the fuel line where it passes alongside the sump?

I assume the carb tower is spewing out water into the top of the rad as it should?

Rich
 
all the rest of it is fine - having just completed some 300 miles or so in the Dales and Lakes, and about 3K miles with no change, it seems odd that it would just decide to do it. Need to re-check the carb tower again, an easy check. Might have been rubbish in the fuel, but plenty filters about. It's strange, cos it's not like it's hot...

Some things may have slipped (timing, mixture etc). It's either running KO or KK needles, I can't quite remember. Goes very well...
 
Hi Rob,

Sounds like the problem is just the fuel. Given that it was still doing it with the electric pump on does sound unusual, but as you say, the fuel was boiling in the filter.

Hopefully a fresh tank of higher octane fuel will correct the problem.

Ron.

P.S: It doesn't have to be hot for vapourisation to occur. Can occur at less than 10 degrees C provided the fuel is rubbish enough!
 
Ta chaps, must be fuel.... I'll be steering clear of Esso 97 then for the forseeable future, unless they change it over lots...
 
HI rob may not be your problem but have had issues with reserve taps that once cable pulled out and pushed in after use outer cable becomes dislodged causing tap to be in its central travel blocking main/reserve ports giving poor fuel supply.Also i would check return line back to tank for any blockage.
good luck
clive.
 
The return line system can have issues as it returns the fuel heated by the engine bay back into the tank, causing the overall temperature to rise. Higher octane fuel often contains lower boiling point hydrocarbons, particularly in winter as it doesn't boil out in the station tanks. Esso's summer mix might be much better. All companies vary their blends between winter and summer and according to location and height above sea level. Its actually a rare thing to get two tanks of the same stuff.
 
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