Fuel Vaporisation

Fit heat insulators, I fit and use a choke on my singles for hot starts as well, it works but it needs taking off immediately or it 8 strokes.

Cornwall you say!

All pump fuel in Cornwall contains ethanol. There is a link with this kind of problem and bio solvent.

Hi Ian, I have not had this issue but then I only used ethanol back in 2006/7 when I didn't know about it and found the tank sealant (Petseal) in two slimline tanks had turned to mush and the fuel hose on my Commando decided to spray petrol at the engine from at least half a dozen tiny holes. No wonder this stuff is banned for aviation use.

BP used to be good E0 stuff but the formula has changed recently and I'm pretty certain that it all includes ethanol now. The new ad says something about a green light. Best avoided.

Esso Supreme Synergy 97 RON BS 7800 is guaranteed E0 but as you know, not in Devon and Cornwall (Or Teesside and Green Scotland... Not so bonny now, hey, Gordon?) Avoid EN228 so check the pumps.

As for the insulator / manifold gaskets: I find a thick one between the Engine and the manifold and a thin one between the manifold and the carb works for me.

Can someone explain this problem to me? I can understand on a car when the fuel in the line from the tank to the fuel pump is vaporized because of excessive heat, the vapor not letting the fuel pump do its thing. But on a gravity fed system where the float bowl is vented to atmosphere, will not fresh fuel run into the float bowl as the liquid there vaporizes? Could you not tickle the carb until you get a full float bowl?

Mike

All I know is the carb gets too hot and the engine will not start, not sure if this is due to lack of fuel or the hot fuel is not effective in some way e.g. the lighter fractions evaporating off. Hence why I have to use a choke on my B44 to get the mixture richer, tickling would work too but as soon as the engine gets going its seems to not need the rich mixture so tickling will be too rich after the engine is running until the fuel level drops. I have heard but not tried that one other solution is to turn the fuel off a couple of hundred yards before coming to a stop, only turn the fuel back on just before restarting and the fuel will be cool. That is no use if the engine stalls at lights. Never had the issue on a Commando with standard setup.

You know this sounds exactly like my 16H, except I know that is down to a hot magneto. Any time I take the bike out I plan my stops for around half an hour. Otherwise no issues and cheaper than the mag rebuild I keep putting off.

When the temp is below freezing you may find carb iceing a problem you have not suffered before, it happened to me after leaving an NOC meeting in darkest Kent a few years ago. I hear its more likely with the ethanol mix.

Tufnol heat insulating washers work. There should be thicker ones between the head and the manifold and possibly a thin one between the manifold and the carb. Carb icing has troubled my 99 since the winter of 1969. When the temperature is hovering around zero and the air is moist or wet, the carb will ice up. Solved by stopping for 5 mins and letting the engine heat warm the carb and melt the ice. Theoretically alcohol in the fuel should help prevent icing (Hawker Hunters had a methanol injection system into the fuel to overcome icing) but it seems to have no noticeable effect with our current pump petrol.

possible tight tappets. combustion taking place in the inlet tract. trying to dissipate the heat through the carbs vapourizing the fuel. Baz

Ian, I think that you can safely disregard vapour lock on a warm? (20 Deg. C day). Here in the anti-pods wehave ridden on dayswhere the day time temperature climbs to 40+ Deg. C and wehaven't experience any fuel (starting)problems.The handle bar levers get so hot in the sun, that gloves must be worn to operate them. The road bitumen starts to soften and tires leave an imprint.......This is using at different times, bikes fitted withthe AMAL 76, 276, 389, Concentric, Japanese Kehin and American S&S carburettors. I think you have an electrical problem.

Paul

Ethanol-containing petrol contains additives to make it burn faster for direct fuel-injection as in modern cars, and it produces more heat. (A Silver Ghost with its original close-tolerance iron pistons may seize if using pump fuel so paraffin may need adding to lower its combustion temperature).

Once your Amal is functioning it will then cool as the fuel vaporises, so probably brief application of the choke will allow the hot start, as suggested above. Works for my 1957 99, albeit with a Concentric rather than the correct Monobloc. A Tufnol gasket will help in summer, but might it encourage icing in winter?

Back in pre-fuel injection days, the way to start a car suffering from fuel vaporisation was to open the throttle fully and keep turning the engine until it started. Not so easy when you have to use a kickstart, I know.