Fuel Reserve - is it really a reserve?

I have read a recent post about a fuel reserve sensor that made me think; what is, and where is the 'reserve'?

Does not the mighty ST have a mega 29L fuel tank, running from full to empty, no reserve?

Thank you.

No reserve. Its 7.2 gallons, I think, and when you get down to one bar it starts flashing and if you hit the fuel rocker switch on the left side of the dashboard the mpg switches over to how many miles you have left based on your immediate history of mpg. it's of varying accuracy - some have reported here that their bike is optimistic regarding miles of fuel left, others not so much. But, since the fuel in the lower tank cools the fuel pump, and heat shortens its life, you might consider filling up at two bars.

I almost ran out of gas, once. Between 20 and 30 miles left in the tank, the readout goes blank. So the last 20 miles to engine cutoff is 'living on the edge'.

It's 7.7 gallons total with 5.5 are in the upper tank with 2.2 in the lower tank. 2.2 gallons left corresponds to two bars of fuel. 1 flashing bar is at least a gallon left in my bike, closer to 1.5 and I consider that reserve. It starts counting down remaining miles that last gallon and at .5 gallons any miles left then switch to zero. This could be at 20 to 25 miles.

Thank you everyone. Very helpful information.

Cheers

Fuel reserve?
Anybody remember ( I know you all do ) reaching frantically under your left leg for the reserve tank switch whilst riding amongst traffic. The good old days when a RD400 was considered a powerful bike.
Upt'North.

I had a 1981 cb750c from 83 to 07 and yes I do remember reaching and remember running out of gas at 2am back in 1984 about 5km from home. We had no 24hr stations back then. It was stay tge night or go for it... I lost. Long walk

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Upt' North said:

Fuel reserve?
Anybody remember ( I know you all do ) reaching frantically under your left leg for the reserve tank switch whilst riding amongst traffic. The good old days when a RD400 was considered a powerful bike.
Upt'North.

Click to expand...

IIRC, my old Moto Guzzi had two petcocks. The fuel lines joined in an 'X' fitting and then went to both carbs. One was the reserve - and I could never remember which one it was.

My BMW has 2 petcocks that are joined to run to carbs. Practice is to open one petcock till it sputters, open other till it sputters, then turn first one to reserve, then if you are STILL stoopit and haven't got gas....turn last one to reserve and pray!!!!
I've never gone beyond opening 2nd petcock.

dduelin said:

It's 7.7 gallons total with 5.5 are in the upper tank with 2.2 in the lower tank. 2.2 gallons left corresponds to two bars of fuel. 1 flashing bar is at least a gallon left in my bike, closer to 1.5 and I consider that reserve. It starts counting down remaining miles that last gallon and at .5 gallons any miles left then switch to zero. This could be at 20 to 25 miles.

Click to expand...

Dave, I know the specs say 7.7 gallons but I actually ran out of gas once (faulty sensor in lower tank) and coasted into a gas station. I put her on the center stand and filled it to the top.... 7.4 gallons was all I could squeeze into her. So, there must be 0.3 gallons of the listed 7.7 that is unusable.

I don't know, I've never run dry and the most I've ever put in was 7.2 IIRC. The gauge had just flipped to blinking zero.

My FJ600 had a reserve petcock but that did not keep me from running out of fuel. The bike was modern enough that it wasn't necessary to shut the fuel off when parking so I never did which made it easy to forget to turn it from reserve to run position and I did run out fortunately pretty close to a gas station. In those days the gas stations would lend you a gas can, now they sell you a gas can.

This is summer we rode from Wawa to the Soo and once you leave Wawa the next gas is 150 plus km, the gas station east of Wawa had a gravel drive filled with potholes and I figured the next place must be better. A 100 plus km later the low fuel light had been on for 60 or 70 km and I see a sign that says next gas 39 km, pretty sure that if the rest of the way is downhill with a tail wind I will run out 20 km short of there. Started looking for a place that might help me out and saw a campground near the Montreal River Provincial Park pulled in and for $5 got 4 litres of gas, the fellow that ran the place was real nice and his daughter had lived in our town. He kind of looked like Grizzly Adams.

Gerhard

I have a old 1976 Honda CB 750 that has the switch from off, to run, to reserve. I have owned this bike for many years and have only used the reserve a few times. What a mistake. I usually take this bike with me when I want to ride when I am out of town and I am driving my pickup. I was visiting my sister and brother in law. My brother in law has a bike so we spent most of a Saturday riding around where I grew up. When we got back home my sister showed interest in riding. But my brother in law was afraid to let her ride because he had never ridden with a rider all those years of riding. So I told her to hop on. We rode another 15 miles and she loved it. About a mile from home the bike ran out of fuel. So I reached down and turn the switch to reserve and we went home with no problem. Back at my home 2 days later, after I unloaded the bike I headed to the gas station to fill up. The bike stopped on top of a long river bridge 2 miles from home. Not because I had run out of fuel but because of all the trash that was in the lower part of the tank. On this old bikes there is no fuel pump it is just gravity flow. And all the trash just sits there until you open the reserve and them it runs out into the filter. The fuel filter was completely full with stuff. The old Honda tool kit came in handy. I got it running and headed back home since it was much closer. Then I went back to the station with a 5 gallon can.

My 305 Scrambler and CB750 had petcocks with the Reserver Lever. While I never ran out of case with either I came very close a few times.

But I did have a problem always remembering to turn the lever back to On from Res. Every so often when I wondered about gas and saw the odd or trip odd reading higher than normal for a fuel interval I'd check the lever and find in still in the Res position. Head for the pumps and find that I almost completely filled the tank.

I'll add one more to the mix. My FZR1000 had an electrical toggle switch that was the 'reserve' switch. Originally I thought it turned an electrically operated petcock to the reserve setting and back. But then I later realized the petcock had no wire attached to it. Apparently there was a low fuel sensor in the tank which would interrupt the ignition when the fuel level dropped below it, and create a sputtering like you felt when going on reserve with a normal petcock. When you flipped the switch the sputtering went away. So it was nothing more than a mental reminder that you were now on reserve.

Upt' North said:

Fuel reserve?
Anybody remember ( I know you all do ) reaching frantically under your left leg for the reserve tank switch whilst riding amongst traffic. The good old days when a RD400 was considered a powerful bike.
Upt'North.

Click to expand...

For me it was the 76 XS500.

@Rob20111, this thread is 5 years old. No problem here, we all post to an old thread sooner or later.

SMSW said:

@Rob20111, this thread is 5 years old. No problem here, we all post to an old thread sooner or later.

Click to expand...

Hey, I'm 60 now, I'm allowed. LOL

my Yamaha stays in reserve; my XL stays in reserve; only in highway traffic at 110 / 70 mph, done with that.

STumped said:

Dave, I know the specs say 7.7 gallons but I actually ran out of gas once (faulty sensor in lower tank) and coasted into a gas station. I put her on the center stand and filled it to the top.... 7.4 gallons was all I could squeeze into her. So, there must be 0.3 gallons of the listed 7.7 that is unusable.

Click to expand...

The whole problem with fuel level is the sensors will not be accurate if you don't take the level down after about 5 fills.
I noticed the reserve feature started tripping earlier and earlier, so I tested it.
I took a Rotopax can off another bike and stuck it in my top box when I was able to time the reserve to kick on when I was home.
When I first got the bike I measured around 340 miles before the reserve light went on.
Then it started kicking on around 300 miles.
Granted I started riding a lot more aggressively, but that was a big drop.
I took off and went for a ride with the spare gas and the reserve was showing 42 miles.
I didn't ride out the tank because I didn't have time but it stayed at 42 mile range for several miles before dropping to 41 mile range.
I rode a 20 mile loop but it still showed 35 miles.
I called the dealer's service dept the next day and was told the level sensor "recalibrates" itself and if never run low it will have errors indicating less gas than what is actually present.
They said the best practice is to run it partway down on reserve.
I've noticed about every 5 or 6 tanks the levels seem wonky.
That reserve flash and miles left feature is automatic on my bike.
Don't know if that's a setting, I got mine with 1500 miles on it in mint condition.