Vacuum Fuel Tap

Quite a while back there was a posting where someone said the vacuum fuel tap can be converted to non-vacuum. Not much detail was given. I have just pulled my vacuum tap apart and it appears that this can be done. The steps involved are:

• Remove the vacuum diaphragm valve.
• Plug the vacuum valve seat.
• Plug the vacuum port to the carburetor or make a backing plate (Remember to cap the carburetor vacuum pipe).
• Make some seals to go where the diaphragms were or just remove the o-ring and spring leaving the diaphagm in place.
• Reassemble the vacuum side.
• Turn the tap upside down and possibly remove approximately 2mm from the handle so it does not hit the tank.
• Insert the spring washer and replace the chromed label plate upside down and tighten the screws back up.

I have tested this with air and the position assignment is now:

• Res = Res
• On = On
• Pri = Off

Photo: Tap in ON position.

Has anyone tried this and were they satisfied with the outcome?

Thank you for any feedback.

I think the original "plan" you're referring to was done on the two petcock tanks. It involved swapping the levers from side to side. That way, there wasn't a need to run the lever upside down like you've done. Details on the conversion are on the 650 Wiki site.

Thank you for the background 5twins, it made me think. I will speak to my machinist friend and get his opinion regarding filling the existing channels in the tap and milling new mirror images. It could save we about £57 here in the UK on the price of a new tap. The milling would be free.

Thank you.

xsjohn did the conversion/adaption. Details may be in 650Skulls "xsjohn's mod thread" or the old 650 Rider site.

Paul Sutton said:

Quite a while back there was a posting where someone said the vacuum fuel tap can be converted to non-vacuum. Not much detail was given. I have just pulled my vacuum tap apart and it appears that this can be done. The steps involved are:

• Remove the vacuum diaphragm valve.
• Plug the vacuum valve seat.
• Plug the vacuum port to the carburetor or make a backing plate (Remember to cap the carburetor vacuum pipe).
• Make some seals to go where the diaphragms were or just remove the o-ring and spring leaving the diaphagm in place.
• Reassemble the vacuum side.
• Turn the tap upside down and possibly remove approximately 2mm from the handle so it does not hit the tank.
• Insert the spring washer and replace the chromed label plate upside down and tighten the screws back up.

I have tested this with air and the position assignment is now:

• Res = Res
• On = On
• Pri = Off

Has anyone tried this and were they satisfied with the outcome?

Thank you for any feedback.

Click to expand...

That is interesting. Since you have yours apart, what would happen if you got rid of the diaphragm and the whiteish plastic wafer, then just assembled the two halves with gasket paper between them? Does that give the same pathways you're seeing? With lever and faceplate still upside down of course.

XJ I thought I remember you "fixing" one with epoxy one time?

The vacuum tap from my SH works as follows:

• Fuel gets to the outlet at the back by either passing the diaphragm valve's o-ring at the back or via an independent route from the front as in the prime setting.
• In the reserve position the fuel flows from the reserve intake through a channel in the front of the tap which directs it back past the o-ring of the diaphragm valve and then to the outlet.
• In the on position the fuel flows from the higher fuel intake directly via the diaphragm valve to the outlet.
• In the prime position fuel from the reserve intake is directed by the channels in the tap through a route independent of the diaphragm valve to the outlet.

Xjwmx - If you just remove the diaphragm valve and plastic block and put the tap in upside down this will leave a direct route for fuel to flow to the outlet totally independent of the tap. This is the same situation as when the diaphragm breaks. You must plug the diaphragm valve seat. By plugging the diaphragm valve's seat at the back and turning the tap upside down this forces the fuel via the channels in the tap out through the independent primer route to the back of the tap and to the outlet.

I see three possibilities for this conversion once the valve seat has been plugged with an insert or the original diaphragm valve:

1. Turn the tap upside down as originally suggested, or
2. Cut off the tap lever and fit a new lever in the down position, or
3. Make a new tap on the lathe with the channels cut as per the original tap and a lever fitted in the down position ie. diagonally opposite to where the original lever would have been.

I am going to attempt making a new tap so I can have the tap lever facing down, make a blanking plate for the back and store the original parts - I hope this makes sense.

This may help Paul Sutton?
From xsjohn (RIP)

Thank you for that weekendrider. That seems a much easier conversion and just involves drilling one hole and the plugging the valve seat. I am off to examine just how thick the metal is.

gggGary said:

XJ I thought I remember you "fixing" one with epoxy one time?

Click to expand...

No, but I got rid of the diaphragm and the white wafer and put gasket paper between the two halves. That gives you on=on, res=res, and prime=res. I put an inline on/off valve downstream.

I can't picture the inside of the petcock at the moment. Would the gasket paper do the same thing as the aluminum plug in xsjohn's mod? Might a little screw and nut with two washers work in place of the plug (easier to obtain)?

I went off and measured the metal thickness on the tap and decided that it was too thin for me to risk drilling. Instead I made a new fuel tap lever from aluminium on the lathe. I basically copied the old lever dimensions and drilled the channels in the back of it in the same layout as the original. I drilled and tapped a hole diagonally opposite to where the original lever would have been and fitted a nice little s/steel lever made from scrap. I plugged the diaphragm valve's seat with a brass insert and the same for the hole where the vacuum line from the carburetor is fitted. I removed the plastic block and converted one of the diaphragms into a seal. Fully assembled it gave Res = Res, On = On and Pri = Off.



I am happy, had some fun on the lathe and saved a bit of cash. Thank you for all your thoughts and xsjohn (RIP) for providing an excellent alternative for those who can drill more accurately than me. My bench drill is crap with too much slop in it, I could easily be 0.5mm out and wreck the tap.