vacuum bypass on fuel tap

Hi people,

I’m having big problems with the vacuum diaphragm that doesn’t allow fuel from the tank. As I have the bike sitting at work I need to bring it at least home, about 7miles.

I read on internet that some people bypass the vacuum making the tap with free flow(mostly on trackbikes though).

My question is: if I manage to do this modification is there any risk that the fuel will overflow the carbs???

Otherwise i will open the tap for few seconds and then close it for few minutes and so on till i get home ???

oh, it’s a 1991 cbr 600

cheers guys

no you won’t have to keep turning the tap off, the carb’s will only overflow if a float gets stuck open…

Stick it on prime I think

Common fault … I have 2 fuel taps now . One for on one for off . If you do go to a constant flow tap and you park on your sidestand switch it off or the angle can cause it to fill your low side carb and backflow out the air filter . I think the angle maybe affects float perfomance in some carbs .

maybe maybe i sorted it out,

changed the diaphragm properly, covered the vacuum hose with black tape (as it looked a bit worn so could have some air leak) and yes!

It didn’t starve and I managed to go home… i will monitor it next few days for leaks and stuff…

Martin you are right, it shouldn’t but it’s an old bike you never know…

Alex my tap only has on, off, reserve. My mod would have turn it to a permanent prime, which is a bit risky…

Numnum, how do you have 2 taps? I would have switched it off when stop, my concerne was not to empty the carb bowls quick enough having a costant fuel jet, for trackbikes is fine 'cos they are full trottle most of the times but definetely not my case…

thanks anyway guys

There is my twin tap setup … The original tap has ON or reserve no off , The second tap has on and off . Carbs dont overflow from constant fuel, many bikes were made before someone put a vacume tap on them. It’s there as a health and saftey device as much as anything to try and prevent fuel spills in event of hose burst or crash .

I think Peppiiino has done the logical thing and half sorted the problem.

The usual problems with vacuum fuel taps mostly come down to a dodgy diaphragm or an air leak in the vacuum hose.

Both are pretty cheap and easy to change once the tank is drained which gives a good chance to do that often neglected task of cleaning the fuel tap/tank filter. (If fitted.)

Oldguy, luckly i have the off position so it wasn’t necessary to drain the tank…

looks like a nice bike Numnum…I love these old machines

I recognise that bike, thought that might be you numnum :smiley:

Yeah it stands out a bit from the plastic coated crowd :smiley: