Bubbles from fuel pump?

[Falco Frank]

I did ask the same Q on a FB forum first but will delete it after multiple know-all muppets answered...

A bit odd-ball.
I put some fuel stabiliser in the tank yesterday and ran the bike up, no problems at all. I let the fans cut in and all was well.
The fuel level was low so I had a quick look in the tank before shutting off and noticed bubbles coming off the fuel pump and a 'misting' in the tank?
The misting cleared in a while but, the bubbles kept appearing, every 5 seconds or so...
'Just' a function of the fuel pump or could something be amiss?

Just remembered my chemical industry background and pump Cavitation springs to mind!

Regards - Frank

[Firestarter]

Are the bubbles coming from the pump body, or from a fitting? i.e. is it bubbles that have settled on the pump that then get dislodged, or is it a stream? I had a small stream when fitting the carbon tank, which was the potting around the screw fitting not being properly sealing.

I don't think it's cavitation - that's in the low-pressure side of the pump, and the bubbles tend to collapse as they go through the pump and reach the high-pressure side (in this case they would be petrol vapour, so they'll just get re-absorbed into the liquid fuel when the pressure increases again).

The only time I've noticed misting was after filling up, think there was some sediment in the fuel supply. Not sure on that one - could be a contaminant in the fuel, which is also the source of the bubbles as they coalesce on a suitable surface?

[moggyvan]

As I stated on your original FB post- check the immersed fuel hoses inside your tank as they are now commonly failing due to ethanol in our petrol.
Mine failed on my Futura last year….
AP Workshops do a kit consisting of hoses, filters, main oring seal and clamps for a very reasonable price.

[Falco Frank]

Many Thanks guys, its hard to tell the exact source as the fuel level was just above the fuel pump.

I replaced all the fuel hoses with fully submersible a few years ago (and lockwired too!).