Air bubbles in petrol pipe/is it causing fuel starvation

[bristolmod]

these "bubbles" are normal! At least they are on the 100+ Lambrettas I've owned since 1968

Chris

[cookie81]

these "bubbles" are normal! At least they are on the 100+ Lambrettas I've owned since 1968

Chris

thanks chris

I should stop reading forums as all it does is make me paranoid about what might go wrong!

[mark]

my problem was nothing to do with tap in end my vacuum feed pipe was blocked and now i have reverted to the cam lam /light tap as it has a faster flow than either of the kace fast flows i have .

[alex_hughes]

Interesting thread... just fitted a camlam rear exit fuel tap on an engine which had run faultlessly for several thousand miles, and its nipped up at 6000 revs.

I checked the fuel flow when I fitted it, and it did a pint in about 40 seconds. So on the face of it you would say that it was ok.

But i didnt make any other change to the setup. And it never once nipped up before.

So you have got to wonder about how the tap performs at speed. When I fitted it I thought that the pipe inside the tank was a bit narrow, might take it out and see what happens

Alex

[gadgetman]

This is a common problem and is due to the fact that on a PWK carb the fuel inlet is from above not below as is the case with DellOrto's etc. Every time the float valve opens to allow petrol into the float bowl air rises into the fuel pipe. The way to cure it is to find a way for the air to escape back to the tank by fitting a 'Y' or 'T' joint to the highest part of the pipe close to the carb and running a 'breather' pipe vertically and back into the top of the tank.

[Andy Pickering]

these "bubbles" are normal! At least they are on the 100+ Lambrettas I've owned since 1968

Chris

Yes Chris its normal to have odd bubbles in the petrol pipe but mine was one long line of bubbles with the rear exit on and did have a nip..now removed and re fitted camlam fast flow tap and odd bubbles in pipe not a long line of bubbles like I had..

[bristolmod]

point taken!

I'm actually concerned when there is no "bubble" as it indicates that the float valve (on a standard carb) isn't working

Chris

[Andy Pickering]

point taken!

I'm actually concerned when there is no "bubble" as it indicates that the float valve (on a standard carb) isn't working

Chris

Know what ye mean Chris..mine was awful TBH bit like going onto reserve..but all the time..

[rps123]

After speaking to Allens Performance in Nottingham regarding the air bubbles i was put right to the fact this is completely normal and affects nothing, when i told them my flow times at a pint then how much i flowed in 5mins the rate is more than double the required amount. So i went back round the roundabouts and after lots of changing of parts i found the problem to be the exhaust. A simple task of taking mine off putting another on and down the motorway at 75mph and no seizes. Should have done that first before changing barrel and piston, new cdi unit, adding augusto, new stator plate, 3 new fuel taps etc etc. All the time it was the exhaust. This was brand new on when i finished the engine. Is now off.

[soulsurfer]

So you're saying your Devtour was causing your siezures? It sounds like your carb wasn't set correctly for your pipe and you've not solved the problem. What pipe are you using now?