Thread: Bubbles in my fuel :(

Not sure about the volume of fuel, but I would expect a bit more than that in 30 seconds.

Bubbles in the fuel indicates that it is sucking in air somewhere; check all of the fuel unions for tightness and any rubber hoses for splits, cracks, or hardness and check the hose clamps as well,

Cheers Charlie

At that rate, it will do a litre in roughly 1 1/2 minutes. At 20l/100km this means it would take 30 minutes to pump 20l, and even flat out you won't get anywhere near 100km in 30 minutes, and you should get better economy than that, so the answer is, yes, that should be enough - but not by as large a margin as I would have expected.

The bubbles suggest an air leak somewhere, with pipe unions and the water trap bowl gasket on the pump being the main suspects, but it could be, for example, a small leak on the diaphragm of the pump. It is also likely to be exacerbated by any restriction in the supply line, typically the strainer on the fuel pickup being clogged.

John

Thanks for the replys
The rate of fuel (2/5 of a bottle of wine) was cranking from the starter for thirty seconds.
I have spent the day cutting the end off frayed hoses (but no luck)
The hoses are not new but they are fair.
I take it from your replys that it is not normal for air bubbles to be sucked through.
The fuel was being forced into the carby at 4psi and held 4psi when i stopped cranking.
I will checkout the pump ant trap asap. However when i take it off will i need a gasket or Oring kit to do a propper job?
How does the water trap work?
Should it be emptied now and then?

Thanks Steve

4 psi sounds about right, anymore than that will cause the carburettor to flood. If it is holding that pressure, then it tends to discount the diaphragm being holed.

You say it has 3 fuel tanks, so the symptoms suggest an air leak which is common to all three - try looking down-stream of the tanks, such as unions past where the fuel lines become one; or pinholes in the pipe. The fuel volume at cranking speed sounds OK; I thought you meant with the engine idling; which tends again to point to an air leak somewhere.

Check out the pump thoroughly; a new diaphragm and gasket wouldn't cost much; and no it is not normal to have bubbles. Change all of the hoses for new ones,

Cheers Charlie

It's been over 20 years since I sold my IIa (still sorry I did) so a lot of water has flowed under the bridge, but from my memory there wasnt much bubbles at all. I would check your pump diaphram to see if it has any leaks in it or if it is sealing properly and not sucking air.


thats my two bobs worth

Blythe

Bubbles are not normal and I know where they are coming form if you are using either the old school replacement electric solenoid changeovers or the old brass tap fitting., those points.


usually if the diaphragm in the pump lets go you will also pump the fuel into the engine oil and it wont hold or make much pressure

4psi is nominal as already mentioned But you should also test it with the engine running. occasionally they will pump harder at higher RPMS use your same test jig but before you hook it up warm up the engine then restart it with the line off of the carby blocked completely and see what you come up with.

while the engine is running once you get to peak pressure if you have any needle shake on the pressure gauge your pump needs cleaning/rebuilding.

the seal on the filter bowl occasionally goes brittle and leaks but is generally good once replaced for 10 or 12 cleanings of the bowl.

the water traps work on the simple principal that fuel is lighter than and imiscable in water so if you get a flow of liquid moving slowly enough across a bowl any water will simply fall out of the fuel to the bottom and clear fuel can drain off of the top.


cheers.

The water trap took forever to get off, I ended up prising the clips?? The gasket looked fully sealed. Can i buy this gasket by itself or do I require the pump kit??

I have not tried the pressure with the engine running yet?

Does the pump and water trap require priming after having it out to start the fuel moving??