I'm replacing the tank on my baby drag with one from a 1950s triumph tiger cub. I know the stock tap on the draggie is vacuum operated, and has three hoses connected to it. One of them will obviously be the vacuum line, the other one must be fuel, but does anyone know what the third line is for? Is that the prime supply? I haven't really had a chance to have a good look at where all these lines connect to the carb.

As far as I'm aware, there isn't any reason why running a standard free-flow tap would be an issue, so long as the float does it's job - I believe the tiger cub tank's tap has an "off" position anyway just in case I park on a hill or at some silly angle. So I guess I'd have to blank off the vacuum line. I'm wondering though which of the two fuel lines I'd connect to the single fuel line from the tiger cub tank's tap? Or if it even matters which one? I'm assuming that one or the other would need to be blanked off.

Would very much appreciate any assistance.

I dont't recall there being 3 lines to/from mine.

Fuel feeds into the petcock from the tank direct by gravity

One line from the carb rubber to operate the vac and open the valve

Second line feeds into the carb

Prime operates by permantly opening the valve and by-passing the vac

On your new tank/petcock, you'd have to blank off the outlet on the carb rubber. You should be ok with the cock in "open" while running, but remember to switch to "off" when stopped or the carb may flood

I dont't recall there being 3 lines to/from mine.

Fuel feeds into the petcock from the tank direct by gravity

One line from the carb rubber to operate the vac and open the valve

Second line feeds into the carb

Prime operates by permantly opening the valve and by-passing the vac

On your new tank/petcock, you'd have to blank off the outlet on the carb rubber. You should be ok with the cock in "open" while running, but remember to switch to "off" when stopped or the carb may flood

I'll have another look then, maybe I'm remembering it wrong. If it's just a single line for the fuel and a vacuum line then it will be a simple matter of blanking off the vac line. Also I've noticed that wemoto and a few others sell a part listed as a "fuel pump" - not sure why the xvs would even need one since it's a gravity fed traditional single carb motor. I'm sure it will be a fairly simple swap anyways.

As for flooding, far as I know the carb would only flood if the float stopped working, so no risk of that hopefully.

wots all this talk of petcocks...yeah I know were kinda fond of them but......!