Air bubbles in petrol pipe/is it causing fuel starvation

[rps123]

Was that on a genuine Keihin PWK as mine is. cheers

[hotwheels]

are the fuel tanks properly baffled inside, if not the fuel may be frothing in the tank

[fred]

would frothing cause fuel starvation?

[Andy Pickering]

are the fuel tanks properly baffled inside, if not the fuel may be frothing in the tank

Mine is, its a Diablo tank...

would frothing cause fuel starvation?

No thats rabies..

[Bufficus]

A pwk carb needs the float needle jet drilled out to 3mm.I had the same issue with mine on my GP.
Its down to the flow rate coming into the carb.One drilled,you may need to get a cotton bud with a bit of autosol and polish the seat up if it doesnt seal.

Have to agree with Soosh. I've had to that mod to severa PWK carbs.

[rps123]

My carb is a KEIHIN PWK 33MM not one of the cheap PWK ones. I flow a pint of petrol through the float bowl in just under 1 minute. But still seem to get this fuel starvation issue only at 6000rpm and above???????????????????????????????????

[soosh]

Was that on a genuine Keihin PWK as mine is. cheers

No,mine was a bgm but im sure its on the genuine ones too.The engines they go on dont need the rate of fuel a scooter needs and a lot have fuel pumps.They work well when done but the fuel/air ratio aint great as with the mikuni.Got it on my smallie now.
Also try raising the float height to allow a higher level in the carb,I had to do this recently on a brand new VHST Dellorto.Im sure your find that will fix it.

[gadgetman]

Had the same problem on my Quattrini Vespa with BGM PWK caused due to the fact that the fuel enters the float bowl from the top on these carbs instead of from below in the case of DellOrto's so any air in the pipe has to return up through the fuel tap. I have also had a similar problem on my Lambretta ( which does have a DellOrto carb.) After many years of trouble free running the engine started to cut out due to fuel starvation caused by air bubbles in the fuel pipe in turn caused by a partial blockage in the tap( common fast flow type ) . Changed the tap for another common fast flow tap and problem gone.

[mark]

i changed the cam lam fast flow rear exit petrol tap with light that was on my 250lc for a kace fast flow because of this on sunday and the fuel
starvation problem has gone im glad to say

[cookie81]

I havent had any problems with fuel starvation but the scoot is mainly used fo 20 mile round journey to work and back, i did however change my fuelpipe to the clear stuff and have noticed that i to have air bubbles in the pipe that go up to about an inch long air bubble, this is on a 30mm delorto phbh. when i fitted the pipe i noticed the air bubble straight away so i turned on the petrol and then fitted the pipe to the carb end thinking this would stop the trapped air but have noticed on that the air bubble keeps appearing!

if im reading this thread right is it most likely to be caused by the fuel tap being blocked then?