...about the Fuel Reserve

[corey]

I know I just posted a question yesterday, but another one presents itself:

I was riding my '79 XS11 Special yesterday and the fuel light came on. After running with the light on for a few minutes I went ahead and switched her on over to reserve. The bike didn't seem to like that, however. The tone of the exhaust changed, like not all the cylinders were firing. I also noticed a severe loss in power except for under great amounts of throttle, and even then it was hit and miss. Shortly thereafter I pulled up to a gas pump and quenched her thirst. Of course this made everything right again.

So I'm assuming she wasn't getting fuel. A dirty fuel screen on the reserve line, perhaps? What do you XS/XJ gurus think it might be?

Thanks again!!!!

[John]

Ok, now let me ask you a question...When you say you switched to reserve, which way were the handles of the petcock pointing? Reserve has the handles pointing up. On the XJ petcocks, the selector handle will cover the function that is written on the chrome retainer. ie, the handle will be hanging down when it is in the on position. To the rear is prime, and to the front is off.

[corey]

The handles were over the marking "RESV"... or whatever it has signifying it is on reserve operation. That is right, right?

While we are at it, what is the function of the prime setting on the petcock? Forgive my ignorance. It's just to prime the carbs, right?

[randy]

Lessee..

All of the XS models (and I assume the XJ's) have vacuum actuated fuel systems. Engine vacuum is fed to the petcock, opening a valve to let fuel will flow if the lever is in either the ON or RESERVE settings.

When the engine is off, the fuel is off, regardless of the petcock setting with one exception -- PRIME.

PRIME will flow fuel without engine vacuum. In case you've run the carbs dry, or rebuilt them, use PRIME to fill the bowls.. In case you've let the bike sit for a long time and the fuel in the carbs has evaporated, use PRIME to fill the bowls.

After the bike is running, switch to ON. Don't ever leave it on PRIME or you risk running out of gas. Let me reiterate. If you run out of gas on PRIME, YOU ARE COMPLETELY OUT OF GAS, YOUR RESERVE IS GONE.

Don't ask me how I know this

[Dragonrider]

If you were truely on reserve, (handles over the "res") then I would expect that there is some water/sludge in the bottom of your tank . . . reserve just draws lower in the tank and water goes to the bottom . . .

This happens to bikes that people don't use the reserve on much . . . ANY contamination picked up goes to the bottom . . . and when you finally do need reserve, you get a dose of bleck . . .

[randy]

Good point, Dan.

Maybe it's a good habit to use reserve for a few miles after each fill-up? Just to keep the bottom clean.

[skids]

Other than possible water at the bottom of the tank,
or maybe plugged screens at the reserve part of the petcock filter towers,
there is a slight chance that one of the filter towers has become detached from the petcock and you were actually out of gas. Next time you have the tank off and without much fuel in it, shake it around and see if you can here it clanking against the sides of the tank...

[dpotter58]

Speaking of reserve, how many miles you figure might be in there? Road speed stock bike, about 35 mpg... I thought about carrying a quart with me one time when low just to run it dry and see.

[thumperjsa]

There is one other thought. Pull out your petcocks and see if the filter is there. Under it is the tubes for the petcock. On one of my petcocks, a PO removed all the top parts (Filter, tubes) so I have no reserve on one side. Possible both are missing. No reserve tubes= no reserve.

I put in line filters partially because of this.

In some ways, I like one reserve. This way, when I get down to it and I am running, I only lose two cylinders and not all 4. I switch them both to reserve when that happens.

My mileage kind of stinks on my bike. I get to about 90 miles before I have to go on reserve. I have a standard with 5.5 gallon tank and am on reserve after about 4 gallons. Once I get the valves re-done because the clearances are to tight, I hope that may fix it a little. If not, then it is on to the rings.

[randy]

Dpotter58;

I had an 81 SH which is mechanically identical to your LH. I ran it on reserve until it dried up just to see how many miles I had available. I got 30. So there's about a gallon in the Special reserve.

Has anyone done this with a Standard?

[dpotter58]

Thanks Randy. I have been meaning to run it dry. I think i'll give it a go and see how far i get.