Fuel tap logic??

Laverda Bomber

Laverda Bomber

Hero member
Call me stupid but what is the PRI (presume prime) position for on my fuel tap and why is it that fuel won't flow out when on the other two settings?
Is it working properly or am I missing something??
Someone put me out of my misery!!
 
Not sure what you mean by prime, but on the rgs it's forward or horizontal for off, vertically down is on, vertically up is reserve. Not sure what taps you'd have on the motard though....
 
Drills, down says on. Back says reserve, forward says PRI.
Have seen it before but don't understand.
I thought one of you clever chaps will know for sure.
 
Some bikes have vacuum operated taps,never had it on any I have so don't know anything about then other than they can be problematic.
 
Doesn't sound like standard Lav tap , more like a jap vacuum tap, two hose connections large one for fuel and a one smaller one for vacuum hose from Carbs 
 
Prime allows fuel flow without vacuum to the tap. Fuel will flow from on and res when vac is provided from the manifold. If no flow with vac, diaphragm in tap is not sealing.
 
Thanks Tippie.
I knew someone would shed some light on it.
Pretty sure there is no vacuum hose.
There is the remains of a tube on the tap but nothing back on the carbs.
I'll have a closer look.
Regards
 
I'm pretty sure this type of fuel tap is only used on CV type carbs - well I have only ever seen it used on CV's
 
Prime function is found on vacuum taps only.  Is used to get fuel to the carbs on initial start-up without having to run down the battery and relying on the vacuum to commence fuel flow.

OFF-ON-RES only on Laverdas.

piet
 
Probably not an Italian tap then. My Ducati has a vacuum tap (probably Dellorto) but it has no prime position. In fact it has no handle at all. It's just on when the vacuum is sucking and off when it's not. There's a reserve tap on the other side of the tank which is the only way to prime the carbs.
 
Thanks Cam.
At least I know what's going on now. Not likely I will change it as the base has been cast in the glass tank.
Cheers
Bomber
 
So if you're not using a vacuum line and running on the Prime position, you've got no reserve available. Prime is either drawing from the main feed or reserve feed.

Whach you don't run out of fuel... unless you have a gauge?
 
Bomber, there's no reason not to use the vacuum function, just run a vacuum hose to one of the vacuum ports on a convenient inlet stub. 10s of millions of Japanese bikes do this very happily. Will restore your "on" and "reserve" functions,  and will turn off the fuel for you so you don't have to hope your needle valves always seal perfectly (they don't).
Given the tendency for Laverda triples for hydraulic locking/ bending conrods/ breaking conrods this would be a good thing, especially since your conrods are now over 30 years old.

Ken
 
You must log in or register to reply here.
Back
Top