Fuel taps

[VAL. H.]

Has anyone tried fitting Vacuum fuel taps to an airhead?

SWMBO is a little concerned about forgetting to turn on/off the taps.

Is it generally acceptable to just leave the taps on like we did in the old days on our little Jap bikes, or will they simply fill the carbs and then over flow like the Italian mopeds did.

Val.

 

[steveo]

allways turn mine off everytime i stop ( just part of the routine) those floats do stick, espesh on side stand!

 

[(RIP) Proff]

I turn fuel off, I always have done
I have forgot to turn it back on very occasionally tho'
If it's on center stand it's not to critical to turn fuel off, on side stand it can flood the engine as well as leak out of overflows so essential IMHO to turn it off...
It will become 2nd nature very quickly

 

[Colt]

yes it becomes a habit
or learn the hard way with the flooding or overflow.

oh and remember to use the reserve tap properly.
i learnt that when i left my triumph bonnie on reserve.
next time i took it out ,i ran out of petrol

 

[Valker]

yes it becomes a habit
or learn the hard way with the flooding or overflow.

oh and remember to use the reserve tap properly.
i learnt that when i left my triumph bonnie on reserve.
next time i took it out ,i ran out of petrol

YEAH" did that too few years ago, on my R100 RT, 0600 M6 south RAC man was not to happy with me. Never did it again..............

 

[John Armstrong]

Personally, I use the RH tap in the vertically down position, and the left if the off. So if I need reserve it'll be the LH tap I'll use. But I also have the zumo set up so it'll remind me near to reserve time.

And then you only have to switch on / off one tap.

Worked so far

 

[VAL. H.]

yes it becomes a habit
or learn the hard way with the flooding or overflow.

oh and remember to use the reserve tap properly.
i learnt that when i left my triumph bonnie on reserve.
next time i took it out ,i ran out of petrol

I did that on a Honda 100

 

[Voyager]

Has anyone tried fitting Vacuum fuel taps to an airhead?

I suspect vacuum taps wouldn't work as there is only a short distance from the tap to the float bowl and therefore insufficient 'head' to create suction.

There is probably more pressure from the petrol in the tank than there is vacuum in the fuel lines - so the fuel could still leak. The carb doesn't actually suck the fuel from the tank, it relies on gravity to fill the float bowl.

If you had a fuel pump that was sucking fuel from the tank it would be OK (one hears stories of car tanks collapsing when the breather pipe gets blocked ). But these arrangements don't need taps


Someone will now tell us that it is possible

Bob.

 

[D6]

vacuum is taken from the inlet to hold open a spring shut diaphragm, when the engines off, surely the petrol wont flow?, wont matter how long the pipe is?

 

[Voyager]

vacuum is taken from the inlet to hold open a spring shut diaphragm, when the engines off, surely the petrol wont flow?, wont matter how long the pipe is?

The metering needle will block the main jet (actually the spray bar) when the engine isn't running - but it isn't designed to seal the fuel off completely. And the idle jets are still open.

The problem is with the float bowl which can overflow and run fuel out of the overflow pipe. If the bike is on the sidestand the float needle won't always shut the fuel off completely, allowing it to flood.

This is why there is less of a problem when the bike is on the centre stand and everything is level as the float needle should seal the system (until the float drops through evaporation).

Bob.

 

[bumpmuncher]

I think val means another type of fuel tap similar to the one here http://www.gpzzone.co.uk/gpzzone/technical/fueltap.html this type is mainly found on rice grinders. i think they could be made to work, far easeyer to get used to the standard ones

 

[John Armstrong]

vacuum is taken from the inlet to hold open a spring shut diaphragm, when the engines off, surely the petrol wont flow?, wont matter how long the pipe is?

That was / is my perception. The carb only provides the motive force ie reduced pressure to move the tap into the on position, and this occurs on engine start up. So as long as the starter works, the needles etc etc is immaterial as long as the throttle venturi provides sufficient reduction in pressure due to:

http://home.earthlink.net/~mmc1919/venturi.html

to move the tap in the fuel line.

 

[Voyager]

I think val means another type of fuel tap similar to the one here http://www.gpzzone.co.uk/gpzzone/technical/fueltap.html this type is mainly found on rice grinders.

OK that makes more sense - having a separate vacuum pipe connected to the inlet tract

Just a lot of added complexity though.

I was thinking along the lines of the "Anti-wet Sumping Valves" found on some dry sump motors (typically old British iron that doesn't go out much ). These rely on the suck from the oil pump to get the oil flowing.

Some people fit manual stop valves to the oil pipes . . . which means they have to remember to turn them on . . . . which is almost where we started (but the reverse, and with more dire consequences).


Bob.

 

[Voyager]

That was / is my perception. The carb only provides the motive force ie reduced pressure to move the tap into the on position, and this occurs on engine start up. So as long as the starter works, the needles etc etc is immaterial as long as the throttle venturi provides sufficient reduction in pressure due to:

http://home.earthlink.net/~mmc1919/venturi.html

to move the tap in the fuel line.

Apologies to Digger . I thought you were referring to the diaphragm in the top of the Bing carb and thinking that the throttle slider and needle valve would prevent the engine being flooded.

Doh !

All clear now.

(Note for future . . Engage brain before operating keyboard).

Bob.

 

[steveo]

mate of mine years ago had a gsx750 (vacuum tap) the tap snapped off in prime position. left over night the crank case filled with petrol, went to start in the morning , big bang , jets of flame out the base gasket result- bent crankshaft

 

[VAL. H.]

I think val means another type of fuel tap similar to the one here http://www.gpzzone.co.uk/gpzzone/technical/fueltap.html this type is mainly found on rice grinders. i think they could be made to work, far easeyer to get used to the standard ones

That's it! Just what I was thinking. I'm not worried about the distance between tap and carb. The gap is easily similar or longer that that on most Jap bikes (or rice burners if you prefer).

Something I've also thought of is fitting a solenoid fuel shut off as fitted to diesel engines.

However the biggest problem would be getting the correct flow rate. This is because most of the m/cycle taps aren't a straight fit. So I'd need to find a remotely fitting type. However these are more commonly found on Mopeds/Scooters of the Chicken Chaser type and are likely to have tubing that's too narrow.

Val.

 

[John Armstrong]

Could the carbtune fitting orrifice be used to generate the suction needed to open a "vacuum" tap?

 

[VAL. H.]

Could the carbtune fitting orrifice be used to generate the suction needed to open a "vacuum" tap?

Yes it could, and is probably the easiest place to put it.


Val.

 

[D6]

Apologies to Digger . I thought you were referring to the diaphragm in the top of the Bing carb and thinking that the throttle slider and needle valve would prevent the engine being flooded.

Doh !

All clear now.

(Note for future . . Engage brain before operating keyboard).

Bob.

no probs