Author Topic: Why the bubbles?  (Read 564 times)

Offline ghwallice

  • Hero Member
  • *****
  • Posts: 546
Why the bubbles?
« on: January 16, 2020, 10:07 »
I've been mucking around with hoses to check float levels on my 3CL, and decided to use them to drain the tank while they were connected. Referring to the photo the hose on #1 showed bubbles for the whole 8 litres I drained, whereas #2 & #3 showed no bubbles. The bubbles travelled down the tube with the fuel, and loosening and tightening the bowl nut made no difference.

WTF?

Any ideas?
Kubota B7300
'54 Royal Enfield Meteor 700 (basket)
Some Laverda's and Guzzi's and Ducati's, my turbo KTM  & her KTM
Glass door beer fridge

Offline CLEMTOG

  • Hero Member
  • *****
  • Posts: 4582
Re: Why the bubbles?
« Reply #1 on: January 16, 2020, 10:37 »
the two that are solid fuel are draining the vast majority of the tank contents, the one with bubbles is not getting the same availability from the it, and is running partially intermittently, tasking only what the other two cannot cope with.
CLEM

Offline ghwallice

  • Hero Member
  • *****
  • Posts: 546
Re: Why the bubbles?
« Reply #2 on: January 16, 2020, 11:05 »
So does that mean under normal operating conditions the #1 carb may not be getting enough fuel? That was my concern when I saw it.

Why would one run partially intermittently? Maybe the carb strainer is dirty or has a different mesh in it, or the left tap is blocked or the left in-tank filter is dirty. The carbs were ultrasonic cleaned a while ago.

I would have thought even flow would be a prerequisite for a balanced fueling?
Kubota B7300
'54 Royal Enfield Meteor 700 (basket)
Some Laverda's and Guzzi's and Ducati's, my turbo KTM  & her KTM
Glass door beer fridge

Offline Grant

  • Hero Member
  • *****
  • Posts: 17040
Re: Why the bubbles?
« Reply #3 on: January 16, 2020, 11:09 »
Suggests to me that most of the fuel flow is coming from the right tap.
Check fuel flow from each tap and see if they are similar.
Often the internal filters on the taps can clog up with rust and general crap.
Also check the filter on each carb where the 2 way banjo fitting mounts.
Check out my FB page, clublaverda.com

Offline ghwallice

  • Hero Member
  • *****
  • Posts: 546
Re: Why the bubbles?
« Reply #4 on: January 16, 2020, 11:11 »
Yeh, definitely worthy of pulling the system apart and finding out why.
Kubota B7300
'54 Royal Enfield Meteor 700 (basket)
Some Laverda's and Guzzi's and Ducati's, my turbo KTM  & her KTM
Glass door beer fridge

Offline Paul H

  • Hero Member
  • *****
  • Posts: 1247
Re: Why the bubbles?
« Reply #5 on: January 16, 2020, 14:17 »
If your exit pipes are long (and therefore siphoning), then probably the flow/draw is exceeding the flow rate available past the fuel taps. Air is then being drawn into the float bowl zone through the overflow holes. Which then goes down into your pipes, mixed constantly with whatever fuel is getting pas the float vales.

From a distance - I don't think you have a problem

Offline Ventodue

  • Hero Member
  • *****
  • Posts: 1256
Re: Why the bubbles?
« Reply #6 on: January 16, 2020, 15:27 »
<snip> The bubbles traveled down the tube with the fuel

I have to say that surprises me.  You mean, you saw complete bubbles of immersed air going down the tube?  Air being lighter than fuel, someone would need to explain how that could happen ...

I suggest what you actually saw was what Clem and Paul described: intermittent pulses of fuel separated by air gaps. Which isn't quite the same thing.  But, as per Grant, it does point to a partially blocked tap or banjo filter  ;).

Offline Rusty Spokes

  • Hero Member
  • *****
  • Posts: 664
Re: Why the bubbles?
« Reply #7 on: January 16, 2020, 18:11 »
Looks to me like the #1 carb is emptying fuel faster than the fuel entering. The float drain is collecting air, at the bottom. Could be because  the float valve is sticking or the length of fuel line above the #1 carb is longer/shorter? Sound weird for sure. If the petcocks flow evenly then may just a quirk with the hose lengths or float valve?

Offline Paul Marx

  • Hero Member
  • *****
  • Posts: 4680
    • Les motos de Paul
Re: Why the bubbles?
« Reply #8 on: January 16, 2020, 18:35 »
How was the bike running is the question.

Paul

Online sfcpiet

  • Administrator
  • Hero Member
  • *****
  • Posts: 8017
  • NRW, Germany
Re: Why the bubbles?
« Reply #9 on: January 16, 2020, 21:00 »
Is the drain tube of the questionable carb tight on the spigot/barb?  Looks like it's sucking air at this point.  No way the air would get into the fuel on its way through the float chamber.  I'm with Haggis, no great problem.

You're using the hoses to check float heights?  Float height has fuck-all to do with fuel level in the float chamber, there is a huge difference.  Granted, the fuel level should be equal in all carbs, showing the floats all close at the same time, but this says nothing about actual float height setting.

piet
180s feel quick, 120s are...      If it ain't broke, fix it till it is.

"A motorcycle is a bicycle with a pandemonium attachment and is designed for the especial use of mechanical geniuses, daredevils and lunatics"  Georg Fitch 1916

Offline Dellortoman

  • Hero Member
  • *****
  • Posts: 12583
  • My wolf mate 6/5/1996 - 3/1/2011
Re: Why the bubbles?
« Reply #10 on: January 16, 2020, 22:35 »
I don't think you can draw any meaningful conclusions from the bubbles. With float bowls draining and all float valves pretty much fully open, the fuel flow is very different to normal operating conditions. I suspect the breather in the fuel cap wasn't allowing sufficient air into the system, so it could be as simple as Haggis mentioned. Two carbs were acting as drains while the third was being an air relief inlet.

If the bike was running OK, don't lose sleep over it.
Location: Tasmania, Approx 4253S 14723E

Offline ghwallice

  • Hero Member
  • *****
  • Posts: 546
Re: Why the bubbles?
« Reply #11 on: January 16, 2020, 23:05 »
Spigot were tight, using tubes just to get a visual of what was happening, petrol cap open, currently working on rejecting 36mm carbs set up for 108 back to 98/95.bike was level on race stand.
For whatever reason it tells me the system is not balanced.....
Kubota B7300
'54 Royal Enfield Meteor 700 (basket)
Some Laverda's and Guzzi's and Ducati's, my turbo KTM  & her KTM
Glass door beer fridge

Offline CLEMTOG

  • Hero Member
  • *****
  • Posts: 4582
Re: Why the bubbles?
« Reply #12 on: January 17, 2020, 11:19 »
Moto Laverda had identified a problem , since the 180's have two fuel taps feeding the outer carbs and the inner carb being fed from double banjo's on those two outer carbs, but on 120's there is a "fuel rail" under the carbs which is fed by the two fuel taps and each carb has its own individual connection to it via single outlet banjo's, this has been fitted to quite a few 180's and may have been stock for the last ones. it would have been better still if the fuel rail had been (say) 25mm diameter, but its not.

we are all talking bollocks here because very likely there is nothing to cause any concern, but I can state that several times when running flat out and approaching the time to switch to reserve, my carbs have shown signs of low fuel level,, making me think that I am low on fuel but in reality not low enough to switch to reserve, but switching to reserve early has solved this, due to an increase in available fuel head (height) the best way (as I have done when racing in 86/87, and with my 42 litre very long distance tank is to have 3 fuel tap outlets on the bottom of the tank.
CLEM

Offline Paul Marx

  • Hero Member
  • *****
  • Posts: 4680
    • Les motos de Paul
Re: Why the bubbles?
« Reply #13 on: January 17, 2020, 17:23 »
We still don't know if it was running properly.
If it was, it could have pink flamingos coming down those tubes which wouldn't signify anything apart from an abuse of alcohol.

Paul

Offline Schurminater

  • Sr. Member
  • ****
  • Posts: 279
Re: Why the bubbles?
« Reply #14 on: January 17, 2020, 19:42 »
We still don't know if it was running properly.
If it was, it could have pink flamingos coming down those tubes which wouldn't signify anything apart from an abuse of alcohol.

Paul

and most probably no leg to stand on  :D ......not even 1 :D