Switching to reserve very early

[Skinner]

1981 GS650GL, stock.

I installed a new petcock from Z1 because the original was completely shot. It works just fine, in that it delivers fuel at all positions. However, I'm quite surprised at how quickly I have to switch to reserve. Last weekend I had to switch at around 115km (70 miles). I immediately pulled into a gas station and filled up but it only took about 8 litres so I know the tank was nowhere near empty. Is this common with a Z1 petcock or is something messed up? I know a 650L has a smaller tank, but 8 litres is just over 2 US gallons. Reserve should be around the 12 litre (3 US gallon) mark. The tank capacity is 16 litres (4.2 US gallons).

Maybe I just have a much larger reserve with this petcock? I'm tempted carry a bit of gas with me, switch to reserve and let it run dry just to see how it goes. At least then I'll know how far I can go on a tank.

Cheers!
K

[Wingsconsin]

Do the math ..

You already know how far you can go on a tank..

Capacity to empty 4.2 gallons
Approx 70 miles on approx. 2 gallons = 35 Miles PER Gallon

So - on 4.2 gallons you should be able to go 4.2 X 35 = 147 miles

Now of course that is be your rough numbers to dead empty . But ...

The point is valid - just do the math -

[Skinner]

Thanks Wingsconsin,

You're right, the math is easy, but that's not my concern. I'm concerned that the petcock might not take me to the bottom of the tank. If I have to switch to reserve that quickly who's to say that the reserve portion of the petcock won't actually take me to empty, or very close to it?

[Agemax]

remove the new petcock from the tank and compare the tubes that go up inside of the tank with the old petcock. the reserve tube should allow fuel flow right to the bottom of the tank. the main supply tube will probably be taller than your original one.
you can always shorten the main tube slightly to give you a better range before switching to reserve

[JTGS850GL]

After market petcocks are not exact replacements and are more generic to fit the most models with the least number of variations. Reserve may be higher or lower then the OEM depending on the tank configuration.

[JTGS850GL]

remove the new petcock from the tank and compare the tubes that go up inside of the tank with the old petcock. the reserve tube should allow fuel flow right to the bottom of the tank. the main supply tube will probably be taller than your original one.
you can always shorten the main tube slightly to give you a better range before switching to reserve

How would you suggest shortening the main tube without damaging the filter screens?

[Agemax]

How would you suggest shortening the main tube without damaging the filter screens?

some models have brass tubes fitted! mine does
or, if it is the other style with the filters all in one, swap it with the old petcock

[JTGS850GL]

Never seen an aftermarket petcock with brass tubes. All the ones I've seen had nylon filter tubes with nylon mesh filters. Swapping may be an option, but not sure if they are all interchangeable. Seem to remember trying it on one of my petcocks that had a damaged mesh filter but they wouldn't interchange.

[tom203]

There are two common petcocks- one has higher main pickup tube than other. My bike came stock with higher one- very annoying on downhills, at 1/3 tank bike would get no fuel. I switched to petcock with lower pickup. Less reserve,but I can run to about 1/4 tank in "on" spot.
This guy sells both types -the cheaper one has lower pickup.Z1 also

http://www.georgefixs.com

[Skinner]

Thanks everyone. It sounds like it's more of a petcock design issue than a petcock problem. I'll remove it and have a look at the pickup tubes just to see if they can be modified at all. Swapping with the old petcock is not possible because it is completely shot after sitting in gas for 21 years. I kept it just so I can show people what it looks like after all that time!

Cheers!
K

[robertbarr]

Thanks Wingsconsin,

You're right, the math is easy, but that's not my concern. I'm concerned that the petcock might not take me to the bottom of the tank. If I have to switch to reserve that quickly who's to say that the reserve portion of the petcock won't actually take me to empty, or very close to it?

That's a reasonable concern. Sometimes I enjoy a long walk, but not the impromptu variety.

I'd suggest a length of hose on the fuel outlet (with the tank still on the bike) and a short length of vacuum hose to attach to the petcock's diaphragm fitting. Suck on the little hose -- it should require less suction than a light milkshake to pull the diaphragm open, and drain the whole tank into a container. When it stops flowing, you can look in there and see how much is remaining.

[BigD_83]

The pickup on both the stock and replacement (OEM) petcock on my 650G kick in at somewhere around 10L used... nothing wrong with it, but it was disconcerting the first time around when I thought I was only getting about 15 mpg

[Skinner]

The pickup on both the stock and replacement (OEM) petcock on my 650G kick in at somewhere around 10L used... nothing wrong with it, but it was disconcerting the first time around when I thought I was only getting about 15 mpg

LOL! That was my first thought too. How the heck did I get only 115km out of 3 gallons of gas?

[Super]

Glad I came across this issue. Just installed a new petcock on the 1100G project bike and it too started chugging for gas way before it should. Switched it to reserve and all was well to get home. Now I know... thanks for posting.