Gasline Bubbles

Wondering why the clear gas line would have intermittent large visible air bubbles travelling upwards to the gas tap after a ride and shutting off the engine. Mk 1 Amals. One big bubble each 10 seconds for a minute approx.

Seen it everytime I use clear line, cure is to fit opaque line then it dissappears

Maybe the warm carb is sending gas vapor back to the tank.
Jaydee

jaydee75 said:

Maybe the warm carb is sending gas vapor back to the tank.
Jaydee

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'Zactly!

JimNH said:

jaydee75 said:

Maybe the warm carb is sending gas vapor back to the tank.
Jaydee

Click to expand...

'Zactly!

Click to expand...

If you're running on the highway if you pull off and fill your gas tank quickly with pay at the pump and restart it, it will start easily. If you wait a few minutes the heat from the engine will transfer to the carbs and you get the gas boiling that you're seeing. It usually takes several kicks to start then and the engine runs rough for a few seconds. I've found tickling the carbs a bit seems to help it start then. If you wait ten or fifteen minutes, the carbs will cool off and the bike will start easily again

The vapor pressure of the warm gas in the warm carbs exceeds the column pressure of the gas in the line.