Can't Empty The Fuel Tank - Valve and Stand-pipe question

I'm having a problem with fuel flow and the reserve. When the main tank empties and I switch to reserve, I'm not able to run faster than about 60 MPH or the engine quits. What I found (and what you are already suspecting) is low fuel flow through the reserve petcock. Today, I pulled both petcocks and found a bit of grit on the finger strainers, but nothing awful. Looking through the petcock reveled that the opening was indeed partially blocked. I took the valve apart and discovered that the hole punched in the rubber seal sleeve (where fuel is supposed to flow) was way too small. It looked like it had been punched with a dull tool giving it a rather small and ragged hole. I reamed it out best I could, but it's still smaller than the inlet. Bottom line, though they look great on the outside, the valves appear rather cheaply constructed inside. Has anyone else noticed this problem. (for all I know, these are after market valves. . . They sure don't look 35 years old). Is there a replacement valve that someone can recommend that is higher quality?

My other question involves the reserve side of the tank. I thought that the reserve system worked was that the hump in the bottom of the tank caused two separate compartments to form as the fuel level dropped and that the trapped fuel on the right became the reserve. Upon removing the petcocks I discovered the main valve has a stand-pipe. This seems like a reasonable way to make a reserve system, but because of the design of the tank it would appear that fuel below the stand-pipe would never make it to the reserve side. Is the tank supposed to have a stand-pipe? And if so, how does the fuel ever get to the reserve side?

I replaced both of the valves on my MK III with a set from Old Britts. Ella told me these were Italian (I think) and were about the best they could find on the market. I have had no problems with them so, but they are still fairly new.

The main side has the stand pipe, the reserve side does not. The hump on the tank does leave fuel on each side as the fuel is used. The main side (the one with the stand pipe) will run out of fuel when it starts to dip below the top of the pipe. You then switch open the reserve side. Since there is not stand pipe on that side, you have more useable fuel. I have been told, and experienced, you can get about 10 miles on the reserve side. I am also told that if things get grim, you can possibly tilt the bike with the reserve side down and get the left over fuel in the main side to drain over to the reserve side and get a few more miles out of the reserve side. Fortunately I haven't had to do that --- yet. Good luck

Bonwit said:

but because of the design of the tank it would appear that fuel below the stand-pipe would never make it to the reserve side. Is the tank supposed to have a stand-pipe? And if so, how does the fuel ever get to the reserve side?

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You're not leaning into the corners enough

RennieK said:

Bonwit said:

but because of the design of the tank it would appear that fuel below the stand-pipe would never make it to the reserve side. Is the tank supposed to have a stand-pipe? And if so, how does the fuel ever get to the reserve side?

Click to expand...

You're not leaning into the corners enough

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This is one way to activate the second reserve. Primary reserve is that amount of fuel on the reserve tap side. Once this runs out, you can tip the tank to the reserve side to get what remains on the main side over to the reserve tap. Kinda handy when you think you abosolutely have no more gas. To work correctly Norton should have made allowance for a balance tube between the two tank halves.

There are or were some Taiwan made fuel taps out there with a design having a rubber insert surrounding the shaft with a hole that turns with the lever. Phil at Fairspares won't stock these anymore as that rubber insert rotates closing off the hole eventually. The BAP taps as supplied to later 70s Triumphs are probably the best solution. I bought these after experiencing the Taiwan taps about 10 years ago.

Make sure your air vent on the gas cap is working. Fuel starvation is also caused by this.

I have switched all my bikes over to the Italian BAP taps. All the others I have tried seem really flimsy and I don't trust them. The BAPs seem very good and are not super expensive. Some people think they are ugly. I just bought a bunch from an eBayUK vendor. Still a good deal even with airmail postage. There are some other taps that are sold by British Bike Connection in Rochester, NY that look awesome. Billet alloy bodies. They are pricey though, about 65 bucks each. I have seen them being sold on eBay now as well so it looks like their distribution has widened out. I'd like to try a pair of these someday.

Bonwit said:

Has anyone else noticed this problem. (for all I know, these are after market valves. . . They sure don't look 35 years old).

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It's a fairly common problem with these cheap aftermarket tubular seal taps,-unfortunately. The original taps would have had conical brass (later plastic!) valves, and a British-made slightly improved (with an O-ring seal) version of these brass cone taps is available. These taps also have a much better flow rate than the tubular seal type.

Bonwit said:

My other question involves the reserve side of the tank. I thought that the reserve system worked was that the hump in the bottom of the tank caused two separate compartments to form as the fuel level dropped and that the trapped fuel on the right became the reserve. Upon removing the petcocks I discovered the main valve has a stand-pipe. This seems like a reasonable way to make a reserve system, but because of the design of the tank it would appear that fuel below the stand-pipe would never make it to the reserve side. Is the tank supposed to have a stand-pipe? And if so, how does the fuel ever get to the reserve side?

Click to expand...

As others have said, the bike can be tipped over to allow the small amount of fuel trapped in the 'main' side to slosh over to the 'reserve' side and this gives you a small 'emergency' reserve.

Alternatively, two reserve taps can be fitted, (or the main tap can be modified by removing the stand pipe?) so that all the fuel on the main side will be completely used up first, but this will not leave much fuel left trapped by the tank's frame tunnel in the reserve side (of a Roadster tank) so the range on reserve will be reduced.

illf8ed said:

RennieK said:

Bonwit said:

but because of the design of the tank it would appear that fuel below the stand-pipe would never make it to the reserve side. Is the tank supposed to have a stand-pipe? And if so, how does the fuel ever get to the reserve side?

Click to expand...

You're not leaning into the corners enough

Click to expand...

This is one way to activate the second reserve. Primary reserve is that amount of fuel on the reserve tap side. Once this runs out, you can tip the tank to the reserve side to get what remains on the main side over to the reserve tap. Kinda handy when you think you abosolutely have no more gas. To work correctly Norton should have made allowance for a balance tube between the two tank halves.

There are or were some Taiwan made fuel taps out there with a design having a rubber insert surrounding the shaft with a hole that turns with the lever. Phil at Fairspares won't stock these anymore as that rubber insert rotates closing off the hole eventually. The BAP taps as supplied to later 70s Triumphs are probably the best solution. I bought these after experiencing the Taiwan taps about 10 years ago.

Make sure your air vent on the gas cap is working. Fuel starvation is also caused by this.

Click to expand...

Thanks everyone for the information. What you describe is what I have, though there is a tab molded in the rubber that is trapped in a groove machined in the valve body. Still, it's pretty cheesy. Think I'll check out the BAP valves.

Thanks

One of the issues with the Emgo taps with the tubular rubber seal is that it is rubber, not neoprene, and subject to swelling if it comes in contact with alcohol, thus closing up the aperture.

Another issue with these taps is the hole punched through for fuel flow is offset slightly from the ridge that locks the seal in the housing. What this means is if installed one way, hole lines up pretty well with the body; if installed 'backwards', the hole - at best - only 1/2 lines up with the body.

I gave up on mine after a month and put my originals back on, which had been leaking. No leaks since I reinstalled them (9+ months).