No fuel delivery....Air in fuel pipe

[johnny650]

i am at a loss to discover how so much air is entering my fuel pipe and not venting back to the tank ?

Every time i come to start the scoot I have to disconnect the fuel pipe from the carb then drain the fuel and air to remove the air and even then the fuel doesn't always flow ?

its driving me nuts . Anyone any ideas where the air could be getting in and why its not venting?
It occurred to me that fuel might be leaking from the fuel pipe when left overnight with the tap off but how and where is air being drawn in ?

I have left the tank cap off but the cap must be venting ok because when I finally get it started it goes like a rocket ......

[garry inglis]

Is your fuel inlet or banjo pointing down or up as it should be up or try a new fast flow tap

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[johnny650]

sorry gary could you explain banjo up or down I'm particularly dim today .

The tap fitted is a new fast flow quality tap but because the knuckle joint has been fouling with the Jetex slide pivot I have bent the petrol tap knuckle joint at quite a sharp angle so its now really hard to turn the tap on and off.

I have been thinking about removing the tap and giving it an overhaul and making sure that it is fitted tightly into the tap and tank to prevent possible air ingress. I am wondering if the air in my fuel pipe is getting drawn in via the petrol tap because of the treatment I've been giving it.

[johnny650]

duh! its finally dawned on me you are referring to the inlet banjo on the Jetex carb .
The inlet is facing out ie horizontal. It won't fit any other way as the banjo would foul on the engine mount or the mag housing

[Daggs]

Johnny, I think you're confusing yourself. The apparent air in the fuel pipe is perfectly usual. To prove it, remove the Jetex float bowl and with the fuel connected and turned on operate the float manually and watch what happens
It sounds to me like you have a starting problem and you are erroneously blaming it on 'air in fuel pipe'

[johnny650]

thank you for your suggestion daggs but I don't think that 4" column of air in a 8" fuel pipe is normal . I certainly never had this previously with my original engine and setup. its not like a few air bubbles !...

This excessive amount of air must be getting in somewhere .......... I believe it is at least a contributory factor in my fuel delivery problem which may include the petrol tap and fuel bowl float/ valve

If you had been following my recent posts you'll see that when my engine doesn't start ,the fuel pipe has a long column of air and the plug stays completely dry. Once I remove the air and bleed the fuel system the engine will start and run but the following day the same problem is back.

When I am able to I will remove the existing fuel pipe and attach a separate fuel bottle with direct fuel pipe and test that. If the engine then starts and runs consistently i'll replace the fuel tap and see if I can get a better arrangement for the petrol tap knuckle joint.
At the moment I have had to shove the petrol tank over 1" just to fit the jetex carb on the maniold and even with that, the knuckle joint has an almost 140 degree kink

[Scooterdude]

Sounds like the vent in the petrol cap is blocked, take the cap off and listen for a rush of air entering the tank and also observe if the column of air in the pipe reduces/disappears.

The position of the banjo wont make any difference what so ever as it is lower than the tank exit in whatever position its in.

You could check the circular gauze that sits behind the banjo just to make sure thats clear.

I’ve had problems with jetex carb banjo’s touching the engine mount, simple solution i found was to stuff some rubber between the tank and the strap raising it up slightly.

[Lambretta67]

My fuel pipe is always about half full of air. Starts & runs no problem

[rosscla]

Why is your fuel pipe 8" ? If it's standardish carb and tap it shouldn't be much more than 4".

[Lambretta67]

Mine is only about 5