Carb fuel bowl dries out on hot days, how common is it?

Maintenance, repair, troubleshooting, etc.
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zoli2750
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Motorcycles Owned Currently: xj600s

Sun Sep 10, 2017 10:51 am

Hi,

around or above 30C/90F the carb bowls are drying out, even the fuel filter is empty.
It happens even in a 20 min coffee stop.
Happens also when the bike placed in shadow.
But starts without hesitation after priming for a while when tank is full, or cranking when it is not so full.
No gasoline on the engine or around, under it.
Petcock is fine, is closed without vacuum.
european carbs

Tried to ask google, but not found even a relevant question on it.

How common it is?
for me it is really frequent

thanks
zoli

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radare
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Motorcycles Owned Currently: '92 XJR600, '92 Seca II
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Sun Sep 10, 2017 1:21 pm

This is not something I've ever heard of or seen. Are you certain its evaporation and not leakage? How hot do your carb bowls get?

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zoli2750
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Joined: Sun Mar 02, 2014 1:57 pm
Region or State: europe
Motorcycles Owned Currently: xj600s

Thu Sep 14, 2017 10:30 am

Hi Radare,

thanks for the reply, it made me more curious.

definitely not sure :) if it is a leak or evaporation,
It happens an all the four pots, on a starting attempt it does not starts on either cylinders, I think it is not dependent on an individual carb.

tried again the google with other search words

some say there could be a vapor lock on hot days, I have to say I have not encountered wit it on my old carburetted cars,
some say the vapor lock symptome can be worsened with faulty gas cap vent.

and there is an other thing
the boiling gas in the bowl can elavate the preassure inside the bowl and pushing the still liquid gas to the venturi where it either evaporates through the airfilter or evaporates through the two float bowl venting breathers if the latter is physically possible
or just pouring down to the intake manifold, but not sure because after a successful start there is no popping in the exhaust.
but to forgo such a pressure problem there is on our carbs the bowl went system.

I have shielded the fuel line, filter with bycicle inner rubber tube, still dries out the line, filter, bowl.
Can not imagine where could it go so many fuel, in such a short time.

when no one other had such an experience, It seems I have a really strange issue.

:)

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