during some experiments on fuel economy, a strange thing happened. I was using a small bottle calibrated in CC ( I dont know its name ).while testing using the bottle mostly I fill upto 250 cc,drive till it is consumed fully and take note of the distance (In Kms). I am talking about motorcycle.mostly I shall get an average millage say 47 kmpl inside the city. but when I fill the fuel tank ( I measure and pour it inside every time and do not believe in the readings of the pumps at the fuel station) and drive I was always getting around 42 kmpl. I was so confused I had to check for leaks in the tank, tire pressure and all sort of other factors which where not the cause. Then I found out two things one cause was the weather, our hot summer, we do not have covered parking and usually park in the hot sun.
Next thing was the rubber insulator that isolates the inlet manifold and the carb. in my motorcycle there was a plastic flange gasket, As I had to put a 1/4 hose nipple for my experiments inbetween the carb and inlet manifold, I replaced the plastic flange gasket with aluminium flange extension with the hose nipple. and this arrangement was conducting the heat from the engine to the carb making the petrol in the carb evaporate. My carb shall hold about 50cc of petrol, so each time i stop the engine for a while 25 cc of petrol would be gone as vapour.if I stop about ten times for consuming one litre of petrol, i would lose about 250cc of petrol. i.e about 25% loss, the engine would have consumed only 75 %. Only then I foundout that modern motorcyles have rubber insulator inbetween the manifold and carbs which I had to follow to save some fuel.
So did you manage to change to the rubber, and did it stop the issue?
Yes, it really helped, but i could not use rubber because the rubber flange I fabricated bulges out while tightening and the hose nipple would come out stalling the engine.I also tried nylon flanges and I had to compromise with hylam flanges.
For more than a month I did not use my portable generator, I was trying so hard to start it and searching for some fault which turned out to be dry tank. I filled the tank with one litre petrol and three litre kerosene (It runs on kerosene and it starts using petrol) about a month ago while checking it. The kerosene is there but the petrol has evaporated . So this made me start this thread to share this experience. The sun gets through the window for about three hours on the generator and took away my petrol.
The point is the hot air from the engine compartment goes below the car heating the bottom along with fuel tank, somebody can check the temperature of the fuel tank after a long run , if necessary can insulate the fuel tank and see the difference in mileage. (caution in selecting the material for insulation it should be fire proof ). One more doubt do any car have a under cover for fuel tank .
The fuel tank filler cap assembly on my motorcycle doesn't sit quite flush. I'm assuming its from the previous owner's wreck.
Anyhow, on hot summer days, with the caps secured tightly on my fuel cans for the lawn mower, I can smell lots of evaporating gas in the garage. I realized last night its coming from the cap on the bike.