The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Amal, Carburation, Fuel => Topic started by: Greybeard on 05.08. 2014 19:33
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I set off to the annual BSAOC Hampshire branch camp on Friday afternoon; a distance of some 95 miles. Just before I left home the bike was drenched by a heavy downpour of rain.
Off I go with a massive rucksack to carry my camping gear and a map in a polythene bag bungied to the top of the tank. After about five miles the engine just died; no spitting or coughing, both cylinders just stopped as though someone had pressed the cut-out button. When I pulled off the road I turned on the reserve tap and she started again. I was pretty sure that I wasn't that low on fuel and when I turned the reserve tap off the engine kept going, but after another few miles, same thing again; and again; and again! I decided that the problem must be dirt or water in the carb. I removed the pipe union below the float chamber, (pre-Monobloc carb) and cleaned the nut/cover and flushed the pipes through. No dirt was found. Great; no more trouble. The club Saturday ride out went without a hitch.
Sunday; pack up and start on the long (bum aching on the single seat) journey home. After a few miles the engine cut out. I drained the carb float chamber again; and again; and again!
After a while I was on a part of the route that I knew so removed my map from the petrol tank. No more trouble for the remainder of the trip!
My theory is that I may have been causing a partial vacuum in the fuel tank because my map bag was over the tank and although not pulled tight may have been blown onto the cap causing a seal. What do you think?
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I'd say your probably right Greybeard.
I had the same problem with my '51 years ago when I made a pad for my dog to sit on the tank. The pad was made with a plastic base then foam and hessian. Took me a while to work out the problem, fixed by replacing the plastic with more hessian. Muskydog did over 100,000 miles on my bikes.
Cheers