I ran my bike out of gas while taking a spin around the block in my subdivision the other day. Luckily I only had to push it a couple hundred feet to the top of a hill then was able to coast the rest of the way home. But this got me wondering about reserve fuel on the Commando, since the petcocks only have "on" and "off" positions. Am I right to assume that one tap is shorter than the other and that's the reserve side? I've normally been opening both valves, thus leaving myself no reserve fuel. I wasn't aware that the two petcocks were different when I installed them on my new tank; so not taking notice of them, I have no idea which is which. Was just wondering if there's a way to identify which tap is which just by looking at it from the outside? I guess I can just leave the valves both open and see which side fuel comes out of first next time I fill it, but I'm curious if there is any physical difference between the two valves (other than the part sticking in the tank).
reserve fuel
- Thread starter Robb2014
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The inlet for the reserve tap is lower down so it's able to draw fuel from a lower level in the tank. Most are marked, but if yours aren't, most people would install the reserve on the left side, so you don't have to take yoUr hand off of the throttle to turn it on. To know for sure you could disconnect both fuel lines and try draining the tank with the right on only, then when it stops dripping, turn on the left and see if you get more.
Brendan
Brendan
The reserve or short tube is on the right side of my tank and the main or long tube is on the left side. I always run on the main tube only and switch to the reserve after the fuel level falls below the level of the main tube pickup height.
Ther is no physical difference between the petcocks externally that I can see. Now that you have drained the tank you can pull both petcocks and determine which one is the reserve and place it on the correct side of the tank.
Ther is no physical difference between the petcocks externally that I can see. Now that you have drained the tank you can pull both petcocks and determine which one is the reserve and place it on the correct side of the tank.
I use the same no riser (stand pipe) on both sides too. My thinking is the hump in the tank over the frame effectivly divides the tank anyway. If one of the petcocks has a stand pipe, the ammount of gas in that side of the tank that is not used because of it will be trapped on that side never getting to the side with the regular petcock. Obviously this reduces the ammount of usable gas in the (not huge Roadster anyway) tank.DogT said:
[/quote]
I use the same no riser (stand pipe) on both sides too. My thinking is the hump in the tank over the frame effectivly divides the tank anyway. If one of the petcocks has a stand pipe, the ammount of gas in that side of the tank that is not used because of it will be trapped on that side never getting to the side with the regular petcock. Obviously this reduces the ammount of usable gas in the (not huge Roadster anyway) tank.[/quote]
I believe that both sides of the tank are connected internally and are not separated.
I use the same no riser (stand pipe) on both sides too. My thinking is the hump in the tank over the frame effectivly divides the tank anyway. If one of the petcocks has a stand pipe, the ammount of gas in that side of the tank that is not used because of it will be trapped on that side never getting to the side with the regular petcock. Obviously this reduces the ammount of usable gas in the (not huge Roadster anyway) tank.[/quote]
I believe that both sides of the tank are connected internally and are not separated.
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OldBalz said:
If you remove a Commando fuel tank and look at the underside you will see that is not the case.
Some fuel always ends up trapped on the side of the tank tunnel that has the 'main' tap, however if the reserve side is completely drained, then leaning the bike right over allows the trapped fuel to slosh to the reserve side, so it acts as an 'emergency' reserve.
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On Triumph/BSA, the reserve tap is normally on the left. Norton is normally on the right, and originally there was a small 'reserve' decal on the tank to avoid confusion. There is no difference between the taps except the main tap has a brass tube inside the pickup screen. Once fuel level falls below the top of the tube, flow stops. Some reserve taps have 'R' stamped on the lever.
If you run the standard main tap/reserve tap setup, you actually have two reserves:
Once the engine falters from fuel starvation, switch on the reserve tap. It will drain the fuel out of the reserve side down to the final 1/2 inch or so.
If you run out of fuel before reaching a station, get off the bike and lean it way over to the reserve side. The couple pints of fuel on the main side will splash over to the reserve side, where you can use it and get another 8-10 miles.
I like the main tap on the left, as its right next to the key - easy to remember to turn fuel on/off. If I run out will riding, I can take my left hand and reach around the right side to open the tap.
If you run the standard main tap/reserve tap setup, you actually have two reserves:
Once the engine falters from fuel starvation, switch on the reserve tap. It will drain the fuel out of the reserve side down to the final 1/2 inch or so.
If you run out of fuel before reaching a station, get off the bike and lean it way over to the reserve side. The couple pints of fuel on the main side will splash over to the reserve side, where you can use it and get another 8-10 miles.
I like the main tap on the left, as its right next to the key - easy to remember to turn fuel on/off. If I run out will riding, I can take my left hand and reach around the right side to open the tap.
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On the fastback tank and maybe the roadster, I can't remember, the tanks are essentially divided and there is no passage from one side to the other once the fuel level drops to where the "hump" separates them. So a good bit of fuel is trapped on either side. Therefore, in order to actually be able to use the fuel in the tank, you need both petcocks to be "reserve" types - with no extension tube. You use one petcock for the main fuel which then allows you to use fuel from both halves until fuel drops below the hump. Then it continues to use fuel from that side of the tank until empty. You open the other petcock and you have the fuel from that side of the tank. On my fastback tank doing this gives around 3 qts of fuel as a reserve. If you do the extension/no extension (normal/reserve) petcocks, you will essentially lose that reserve unless you do as others suggest and tip the bike far enough to get the fuel to spill from one side to the other. But two "reserve" petcocks eliminates the need to do that.
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BillT said:
Depends on year. By 1975 the reserve tap had been moved to the left.
http://britmoto.com/manuals/Manuals/Riders_4.pdf
batrider
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Odd setup then in '75 - On my '72 roadster the reserve is on the right (has a decal indicating RESERVE). But the standpipe is on the left (main) side. This makes sense to me. I have had to tip the bike over on the right footpeg to get the excess on the MAIN side to go over to the RESERVE side when the RESERVE ran out. It worked well enough to get me to the next gas station. It is good to have a reserve reserve sometimes.
Russ
Russ
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So much safer ,reserve on the leftside.
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Torontonian said:
Unless you forget to turn off the main tap, and your fuel bowl inlet valves don't seal, and your crankcase fills with gas, and it leaks through the crank seal into the primary, and you go for a ride three weeks later, not realizing your full fuel tank is now 1/2 full.
Don't laugh - I saw the effects of exactly this happen.
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This is a very old topic that's been around since the dawn of Commandos...before personal computers, internet and chat rooms exited. Norton put the reserve on the right side. Conventional wisedom has been change it to the left as when you start to run out of gas you need to have your hand on the throttle to keep the engine running while using your left to turn on the reserve.
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