reserve gas capacity - 74 roadster - how far can you go?

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First and only time I ran out of fuel was partly my fault for riding with both taps open, but I didn't realise that was why I'd died as the right side of the tank still had plenty sloshing around and visible through the cap opening. Having tested the plugs were sparking only then did I pull the fuel pipes... both dry.
All the leaning and jerking couldn't get that petrol 'over the hump' to the other side, short of unbolting the tank (four on the Mk3... oh how I miss those rubber bands!) it wasn't going anywhere..
Fortunately a very nice man (step forward and take a bow, Michael from Purleigh Vineyards) emptied his chainsaw into the tank and away I went. My call to the RAC is still unanswered (two years on!)
Vowed to carry a short siphoning tube from that day forward.... though I never have!
 
Well you guys stirred things up. Decided to ride mine after a 3 week rest.... did cursory checks found no reasons why it shouldn't run, but it wouldn't... too damned hot to dig into it so out on the wing... No class or primal thrills, although 5 gal. US in the tank & pushing the button shall make the hog wallow on demand.... I just need a cruise is all. It's okay because she turned 41 this year.
 
I'm a bit new to Nortons but not a mechanical novice. Just finished a restoration and would like to verify my understanding of the tank and reserve system. The bike is a '75 MKIII Roadster and these are my assumptions. Any input appreciated.

1. The tank is ~2.5 Imp gal or ~ 3.0 US gal
2. On the MKIII according to the owners manual, main tap is on the right, reserve on the left (sitting on the bike).
3. At least on this model, the fuel taps are just on or off.
4. Neither tap should have a standoff pipe. You obviously do not want one on reserve or you leave fuel in the tank as you sit on the side of the road. You also don't want one on the main as you also possibly leave fuel in the main side of the tank when the reserve runs out because the tank sides are separated as the fuel gets lower. You would then have to get off and lay the bike over to get the fuel to the reserve side.
5. If you are in the twisties and doing aggressive leaning when your fuel is getting low and then straighten out, you may or may not have much fuel remaining in the reserve side.
6. After two refuelings, this one appears to get in the mid 30s for mpg (US). Is this about average?

Curious why Norton did not just fit a bridge pipe at the tank bottoms and go with a single three position petcock. You would at least have a reasonably consistent reserve capacity.
 
4) The main tap has a standoff pipe, reserve does not. I think the assumption with the factory tanks is that both sides will have equal fuel level due to sloshing while riding. That's a guess on my part, and I've never verified that.
 
maylar said:
4) The main tap has a standoff pipe, reserve does not. I think the assumption with the factory tanks is that both sides will have equal fuel level due to sloshing while riding. That's a guess on my part, and I've never verified that.
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Possibly so, but in the real world when levels drop not always the case :-(
 
springs75 said:
2. On the MKIII according to the owners manual, main tap is on the right, reserve on the left (sitting on the bike).
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That doesn't necessarily mean they still are unless they are the original Mk3 taps which have marked plates as previous models had the reserve tap on the right so if you don't know then I suggest you drain the tank and/or remove the taps if necessary to be sure.

springs75 said:
3. At least on this model, the fuel taps are just on or off.
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Yes.

springs75 said:
4. Neither tap should have a standoff pipe.
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Not correct but the main tap standpipe can either be removed or a second reserve tap fitted in its place.

springs75 said:
You obviously do not want one on reserve or you leave fuel in the tank as you sit on the side of the road.
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Correct.

springs75 said:
You also don't want one on the main as you also possibly leave fuel in the main side of the tank when the reserve runs out because the tank sides are separated as the fuel gets lower. You would then have to get off and lay the bike over to get the fuel to the reserve side.
Click to expand...

However, there is normally a standpipe on main, and yes the bike does have to be laid over (or the tank removed) to tip the remaining trapped fuel over to the reserve side.

springs75 said:
5. If you are in the twisties and doing aggressive leaning when your fuel is getting low and then straighten out, you may or may not have much fuel remaining in the reserve side.
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As the bike leans then so does the fuel. It's accelerating and braking that sloshes the fuel around.
 
'As the bike leans then so does the fuel. It's accelerating and braking that sloshes the fuel around. '
If the tank is baffled does this have that much of an effect??
 
springs75 said:
6. After two refuelings, this one appears to get in the mid 30s for mpg (US). Is this about average?
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This seems to vary considerably among our members. My 74 850 gives me 55-58 mpg US. Others only get 35. Riding style, perhaps?
 
springs75 said:
Curious why Norton did not just fit a bridge pipe at the tank bottoms and go with a single three position petcock. You would at least have a reasonably consistent reserve capacity.
Click to expand...

The main argument against such a pipe is that it has to be disconnected in order to remove the fuel tank.
 
Don't feel left out mid-30's perhaps a little more when the old gods are pleased is the best mine has ever seen. I'm pleased the old beast gets that.
 
L.A.B. said:
The main argument against such a pipe is that it has to be disconnected in order to remove the fuel tank.
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As you say, the disadvantage of a bottom cross pipe is when removing the tank. Removing the hose would be easy - just a clamp but having to drain the tank would be a pain. The advantage is no guess work about pockets of fuel in the tank, consistent reserve capacity and I suspect a single 3 way as opposed to two two way petcocks would have been cheaper, even with the bottom hose. Anyway, it's academic as that's not what they did. Just wondering.
 
Well, a standpipe on the main tells me the Norton engineers weren't thinking of places like the Western US. Even off the interstate, the norm is long straight stretches. With a main standpipe, if you empty reserve on one of these, you can be sure there is fuel still on the main side of the tank. I'll either remove the standpipe or figure there is another small reserve, although I would have to get off the bike and lay it over.
 
springs75 said:
As you say, the disadvantage of a bottom cross pipe is when removing the tank. Removing the hose would be easy - just a clamp but having to drain the tank would be a pain. The advantage is no guess work about pockets of fuel in the tank, consistent reserve capacity and I suspect a single 3 way as opposed to two two way petcocks would have been cheaper, even with the bottom hose. Anyway, it's academic as that's not what they did. Just wondering.
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Agreed, it could have been better thought out but seems it just wasn't considered to be all that important.
 
...and again they were too cheap to add a trip odometer and give the poor owner a chance at avoiding a long late night walk.
 
I usually reckon on 90miles , but start looking for a garage at ~75m. Late night garages can be far and few between in rural areas.
 
daveforty said:
I usually reckon on 90miles , but start looking for a garage at ~75m. Late night garages can be far and few between in rural areas.
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That really says it all.

With the closing down of rural gas stations there are many places in NZ after 6 pm where you can go 140 miles plus without a station.

A Roadster tank is useless off the main highways after 6 pm and weekends down here
 
Not entirely different here. One must be well supplied. Therefore, the Interstate trim now.
 
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