Author Topic: Fuel Starvation When Hot  (Read 191 times)

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BILLINGTON

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Fuel Starvation When Hot
« on: 25 April, 2019, 18:56:27 »
My 1932 BSA 500 cc side valve starts and runs fine now Iíve adjusted the Throttle Stop and Pilot Air Screw so that it will tick over slowly when the throttle is closed. However when on a long run the other day I came to a long downhill section, I closed the throttle because I did not need to increase the speed, when I opened the throttle again at the bottom of the hill the engine simple didnít pick up. The motor died and I pulled over to the side of the road. I had been riding for about 20 minutes in 20 C temperature.

By looking at the Primary Air Holes I could see that no fuel was present. I allowed the bike to cool down for a few minutes and pressed the Tickler on the Carburettor, fuel could be seen bubbling an evaporating through the Primary Air Holes. I waited another few minutes then pressed the Tickler on the Carburettor, fuel could now be seen following out of the Primary Air Holes as normal; hence I started the bike and road the 6 miles home without a problem; however I made sure that I didnít allow the throttle to completely close to avoid a re-occurrence of this problem.

I think what may be happening is that the Carburettor is getting so hot that the fuel is evaporating before it enters the cylinder. Does this make sense and if so how can I prevent this from happening.

DEAN SOUTHALL

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Re: Fuel Starvation When Hot
« Reply #1 on: 25 April, 2019, 20:02:10 »
Tufnel spacers are avialable to offer heat insulation for the carb. See Amal/Burlen site for availability

http://amalcarb.co.uk/pre-monobloc/76-276-series/gaskets/spacers.html
BSA: turning ordinary men into mechanics since 1910

BILLINGTON

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Re: Fuel Starvation When Hot
« Reply #2 on: 25 April, 2019, 21:34:19 »
Thank you Dean. I simply wasnít aware that this solution was available.

Bicycle repair man

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Re: Fuel Starvation When Hot
« Reply #3 on: 25 April, 2019, 22:24:28 »
Are you sure its not something simple like the vent in the fuel cap blocked?

BILLINGTON

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Re: Fuel Starvation When Hot
« Reply #4 on: 25 April, 2019, 23:09:35 »
Itís always worth ruling these types of possible causes out; however I know the fuel can is okay. Thanks for the reply Bicycle Repair Man.

BEVANC

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Re: Fuel Starvation When Hot
« Reply #5 on: 26 April, 2019, 08:17:50 »
The carb on my S29 gets incredibly hot once I have stopped - the top is still hot enough to burn your fingers after 10 minutes; I am not surprised you get fuel boiling away. I plan to fit a tufnol spacer. Cheers, Bevan