Petrol reserve tap – how does it work?

#1
When the reserve function is activated, is the normal fuel pipe blocked off? The reason I ask is that I'm contemplating designing an auxiliary petrol tank for my two-stroke Saab (in which oil is mixed with the petrol in the tank), which will contain a super-expensive lubricant that doesn't produce smoke when the engine is cold, and I want to be able to switch from this to the normal tank once the engine has warmed up. I'm hoping to find a suitable changeover tap and am wondering if the P6 reserve tap would do the job.

Thanks

John
 

chrisw

Well-Known Member
#2
Hi John.

There are two fuel lines going from the engine bay down to the tank. One sticks into the tank more than the other, giving you a reserve capability.

When you pull the cable, the tap in your engine bay - look straight down from your brake reservoir and you'll see it - changes the feed from one line to the other.

The only issue with them these days is the rubber o-ring and ethanol - like anything else rubber and ethanol really.
 
#3
Thanks, sounds promising. So the reserve feed is instead of, rather than additional to, the main feed when the cable is pulled? That's what I would need for my proposed Saab arrangement.
 
#4
Another possibility: Ferguson petrol/tvo tractors have a split tank: small part for petrol to start off then larger part for tvo supply once the engine is warm. They have a changeover valve to accommodate the different feeds, usually available from classic tractor parts suppliers.
 

colnerov

Well-Known Member
#5
Hi, Yes it works on a either/or basis. The only other thing that occurred to me is as the precious stuff will be little used will it drop out of suspension in its fuel and cause problems?

Colin
 

cobraboy

Well-Known Member
#6
Hi, Yes it works on a either/or basis. The only other thing that occurred to me is as the precious stuff will be little used will it drop out of suspension in its fuel and cause problems?

Colin
Surely driving the car will keep it mixed, the same as the 2 stroke oil ?
 

colnerov

Well-Known Member
#7
Surely driving the car will keep it mixed, the same as the 2 stroke oil ?
Hi, Yes I suppose so, but with it taking so long to use the fuel up it could go stale. I have never had any dealings with two stroke so I shouldn't really start asking stupid questions I know nothing about.:oops:

30fjrf.jpg

Colin
 

sdibbers

Well-Known Member
#18
To answer your question I’m not sure it shuts off the other tank when switched to reserve. As for the o-rings, use Viton o-rings as they will stand up to ethanol well.
 

roverp480

Active Member
#19
I believe it does shut off the main going to reserve and vice versa . If it were open the fuel pump which is sucking would be able to suck air or fuel could leak out. . When on main the reserve is disconnected and shut off and the opposite on reserve
 
#20
I believe it does shut off the main going to reserve and vice versa . If it were open the fuel pump which is sucking would be able to suck air or fuel could leak out. . When on main the reserve is disconnected and shut off and the opposite on reserve
That makes sense. Sounds like the P6 reserve tap would do the job perfectly.
 
Top