Commando Fuel (Tank) Issue

I have a 1974 Commando 850 Roadster in a glorious Royal Blue Flake. The bike runs like a top, but on the freeway this weekend I began to experience a loss of power related to an obvious lack of fuel. When I pulled over after a harrowing 4-lane change, I still had a significant amount of fuel in one side of the tank.

I have noticed before that the Norton tank does not have any crossover pipe that permits the tank to drain evenly, yet I have not heard complaints from other riders that they cannot get gas from their reserve tap when the gas is on the other side of the tank. Has anybody had a problem getting the gas to distribute evenly in the tank (without having to wiggle around on the bike) and do you have any advice for solving this issue?

Thanks!

nomadwarmachine said:

I have a 1974 Commando 850 Roadster in a glorious Royal Blue Flake. The bike runs like a top, - any advice for solving this issue?

Thanks!

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run with both taps on if it bothers you and just keep an eye on the level

Both taps were on when this happened. The problem was that the reserve fuel was in the side of the tank opposite the reserve tap, but below the level of the main tap. The fuel is getting trapped in one side of the tank and there is no crossover pipe/hose to equalize the levels.

you sure both taps flowing at the same rate then? sound like one is more plugged up than the other

Does your main tap have a standpipe? I don't think it should have one but I have seen them for sale for Commandos.

Must pull the taps to see if one has lower stand up or both are non
reserve higher taps.

hobot

nomadwarmachine said:

Both taps were on when this happened. The problem was that the reserve fuel was in the side of the tank opposite the reserve tap, but below the level of the main tap. The fuel is getting trapped in one side of the tank and there is no crossover pipe/hose to equalize the levels.

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A certain amount of fuel does get trapped on the "main" tap side of the tank, and this small amount of fuel can be regarded as an emergency reserve. When the normal reserve supply is used up, simply stop, and lean the bike over far enough for the trapped fuel to spill over from the main to the reserve side of the tank, but note that you won't get very far on that emergency amount, maybe a few miles, but it might be enough to get to a gas station or at least get off a crowded highway.

Alernatively, use two "reserve" taps, (or remove the stand pipe from the main tap) as then both sides of the tank will fully drain.

Previous discussion: post31687.html

As noted, on the roadster tank and the fast back tank (don't know about the interstate), once the fuel level gets down a bit from full, there is no way for fuel to move from one side of the tank to the other. Typically you have a standpipe on your left petcock and none on the reserve side. But actually, this doesn't work on these bikes because once the fuel drops below the top of the standpipe, that fuel can't get to the reserve side of the tank anyway.

SO...what you want to do is use all the fuel on one side of the tank and THEN switch to use all the fuel on the other side as the reserve. So remove the standpipe from (probably) the left side petcock. Run with that petcock open and then, upon stuttering, open the reserve (right) petcock. You will then be able to run on the fuel trapped on that side of the tank.

On my fastback tank with no standpipes on either petcock, after the left side is empty, there is about 2 1/2 quarts "reserve" in the right side.

You should check this after removing the standpipe. Fill the tank, both petcocks closed. Fit a hose from the left petcock to a gas can and drain that side. Then transfer the hose to the right petcock and do the same, noting how much fuel drains out - that is your reserve.

Removing the standpipe tap on a Roadster gives about a pint tankard full of fuel. If it's carefully poured back in the reserve side, it will give about five miles.

Disadvantage to this technique is that pewter does indeed absorb the fuel taste and it will be two or three rallies before the beer tastes good again.

I love this forum. Thanks!!!

Yes, very helpful guys! I just had the tank off because my reserve tap has gone gummy, and I was wondering about this while draining the fuel from the other tap. Had to keep tilting the tank. I can see how it would work on the road for that last bit of "emergency reserve." Nice. Didn't think about this before...

Yes, very helpful guys! I just had the tank off because my reserve tap has gone gummy, and I was wondering about this while draining the fuel from the other tap.

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If ya ain't got a steel tank then this could serous bad news, ugh.

About 3 wks ago rode '71 with small fiber glass HyRyder tank to
a rally 60 miles. On return, 5 miles after a gas up it fuel starved on
freeway but opening other tap brought normal power back
in a few seconds. 50 miles later topped off tank yet same thing
in a few miles, had to open both taps. This tank is a pint
low of capacity because of the thick Caswell epoxy sealer.
Its not been ridden since so no findings to report yet.

hobot