Chummy fuelling problem

[Rogerchummy]

Yes, Bob, I see your point. However, the vapour causes a blockage because the pipe from the tank to the carb is relatively narrow which allows a small vapour bubble to block it.

By the way, I should have mentioned that the open-ended vent pipe should be long enough to take the venting end above the top of the fuel tank. If it's shorter (eg below the fuel level in the tank) then fuel will come out of the vent tube when the level in the tank reaches that height.

[David.H]

Does the vent pipe act as a sight glass for fuel level?
I fitted a modern in filter on the RK saloon with 22FZ carb & it had the same effect of apparently restricting the flow...I tried it vertical & horizontal  without improvement. I found a small Wipac glass bowl filter the same as fitted to another car & this solved that problem..It didn't stop  the fuel tap getting blocked though, it was totally blocked on one occasion and removing that on my own by the side of the road with a tank full of fuel was interesting, amazing what a head of pressure three or so gallons generates! Stopping the flow while trying to clear the tap was a job that needed more hands than I had available! The FZ was still incontinent on a random basis (usually when stopped at lights!). I have replaced it with a 24T2...excellent choice!

[Terry McGrath]

Those cheap plastic in-line fuel filters are intended for a pressure-fed system. When fitted to a minimum gravity-fed vehicle (with little drop between tank and carb) they can stop the flow at the most awkward times. In my case it was on a busy French motorway.

[Steve Jones]

Those cheap plastic in-line fuel filters are intended for a pressure-fed system.  When fitted to a minimum gravity-fed vehicle (with little drop between tank and carb) they can stop the flow at the most awkward times.  In my case it was on a busy French motorway.

In my case it was in one of those Dutch motorway tunnels that have a minimum speed limit when we were trying to press on to catch a ferry. Escorted out by the cops who were most upset

Steve

[Rogerchummy]

Hi David

Yes. An added bonus of the vent pipe is that, by using transparent plastic fuel line tubing, you can gauge the level in the tank as the level in the vent pipe will be exactly the same as in the tank.

As I mentioned in another of my replies, make sure that the vent pipe is long enough to go higher than the maximum tank fuel level - if it's shorter there is a risk that fuel could come out of the open vent pipe when the level in the tank is high.

[Robert Leigh]

I have read all the previous replies, but none mentions the way the fuel pipe is routed. Copper pipes frequently have a loop or two in their run to provide a small amount of flexibility. It is important that any such loops allow venting of air or vapour: they should only be formed to be near horizontal, so that there is a steady rising route for any bubbles to get back to the tank.

[Rogerchummy]

Hi Robert

The attached shows how the open-ended vent pipe is installed in the fuel line

[David.H]

Thanks for the picture...very helpful.
Looking at other people's arrangements is always interesting! I like the use of a spare 135 jet to hold the Carb top lever in place! And what is the other Tee piece & pipe assembly lurking in the gloom on the right side of the picture....?  !!
Happy New Year to all the readers!

[Rogerchummy]

Hi David

I've never noticed the "phantom t-piece" before !! It is in fact a reflection of the fuel line t-piece - possibly reflected in the open nearside door.

[David.H]

They are breeding !
D