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Fuel tank question.
- Thread starter 40427
- Start date
wecm31
Luddite Looney
I have almost the identical results, if the speed is under 65 mph. Plus a total reserve of at least another 20 miles.
Per Kurt's picture of the petcock internal tubes....I cut my reserve in about half to eek out that last few miles. With inline strainers, I'm not too worried about sucking the last few dregs out of the tank. Rather ride that last five miles than walk.
louieskretas
Member
1981 R100CS fuel consumption
Hi guys, I have been measuring the fuel quantity and consumption on my "new to me"1981 R100CS to see how far I can go between fuel stops on longer trips.
Here is what I have found.
On normal commuting on mostly secondary roads doing 80 kph revving approx. 3500 to 4000 rpm I sputter and go to reserve at 300 to 320 km. when I switch to right side reserve and turn off the left side I get another 20 km to empty on that side. I look in the tank and there seems to be about an inch of fuel still in there. If I go to reserve on the left side I get almost 50 km before it sputters but there is still fuel visible in the tank.( different length reserve tubes maybe)
This weekend I went on a longer trip 2 up, 65 % highway at 120kph(114 on the gps) and 35% backroads at 60 to 80kph with stop signs every few kms, here is how it looks:
From a full tank with the fuel 1/4" above the bottom of the filler neck I went to reserve at 350km. I turned off the right side petcock and went on left reserve and continued to the next gas station at 394 km( 244.8 miles). I refilled the tank to the exact same level as before and I got 19.74 litres.
( 5.21 us gallons)
At the same consumption this means that the main tank before reserve has a 17.6 litres or 4.65 us gallon capacity.
This works out to:
19.96 km per litre
46.95 mpg us
56.38 mpg imp
5.01 l/100km
If I assume that I can get at 23 litres of tank capacity my range should have been 23 ltr x 19.96km/ltr = 459 km.( 285 miles)
The specs say it is a 25 ltr tank ( 6.6 us gal) and I am assuming that there is approx. 2 litres of fuel that is below the bottom of the reserve tubes.
cheers
Louie
Hi guys, I have been measuring the fuel quantity and consumption on my "new to me"1981 R100CS to see how far I can go between fuel stops on longer trips.
Here is what I have found.
On normal commuting on mostly secondary roads doing 80 kph revving approx. 3500 to 4000 rpm I sputter and go to reserve at 300 to 320 km. when I switch to right side reserve and turn off the left side I get another 20 km to empty on that side. I look in the tank and there seems to be about an inch of fuel still in there. If I go to reserve on the left side I get almost 50 km before it sputters but there is still fuel visible in the tank.( different length reserve tubes maybe)
This weekend I went on a longer trip 2 up, 65 % highway at 120kph(114 on the gps) and 35% backroads at 60 to 80kph with stop signs every few kms, here is how it looks:
From a full tank with the fuel 1/4" above the bottom of the filler neck I went to reserve at 350km. I turned off the right side petcock and went on left reserve and continued to the next gas station at 394 km( 244.8 miles). I refilled the tank to the exact same level as before and I got 19.74 litres.
( 5.21 us gallons)
At the same consumption this means that the main tank before reserve has a 17.6 litres or 4.65 us gallon capacity.
This works out to:
19.96 km per litre
46.95 mpg us
56.38 mpg imp
5.01 l/100km
If I assume that I can get at 23 litres of tank capacity my range should have been 23 ltr x 19.96km/ltr = 459 km.( 285 miles)
The specs say it is a 25 ltr tank ( 6.6 us gal) and I am assuming that there is approx. 2 litres of fuel that is below the bottom of the reserve tubes.
cheers
Louie
Louie -
Not sure what spec you're looking at or you might have a different tank, but one online site says the R100CS has a 6.34 gallon tank. That's essentially the same as my R100/7.
I've been keeping track of my gas mileage for years. I'm averaging the same 4.6x gallons from full to the first reserve...I don't fill the tank nearly as full as you though. That leaves about 1.6 gallons or so and about 0.8 gallons in each "saddle". My averages for the gallons in the first reserve (I typically use the left half of the tank...easier to get my hand on that petcock quickly when it flames out) is around 0.75 gallons. Generally speaking then, there's going to be another 0.75 gallons in the right saddle...it might be different due to the different shape of the tank tunnel due to the under tank master cylinder. So, I'm guessing that I'd have about 0.1 gallons of "unusable" fuel. Note, that if desperate, I take the take off and tilt it to pool the two small amounts together to get another 10 miles down the road.
Suggesting there's 2 liters of fuel below the lower petcock straw seems like a lot. Either you do have a bigger tank or it could be your lowest straw is significantly taller than most. There are no set dimensions but Snowbum has listed about 83mm for the tall straw and 23-24mm for the short straw.
Not sure what spec you're looking at or you might have a different tank, but one online site says the R100CS has a 6.34 gallon tank. That's essentially the same as my R100/7.
I've been keeping track of my gas mileage for years. I'm averaging the same 4.6x gallons from full to the first reserve...I don't fill the tank nearly as full as you though. That leaves about 1.6 gallons or so and about 0.8 gallons in each "saddle". My averages for the gallons in the first reserve (I typically use the left half of the tank...easier to get my hand on that petcock quickly when it flames out) is around 0.75 gallons. Generally speaking then, there's going to be another 0.75 gallons in the right saddle...it might be different due to the different shape of the tank tunnel due to the under tank master cylinder. So, I'm guessing that I'd have about 0.1 gallons of "unusable" fuel. Note, that if desperate, I take the take off and tilt it to pool the two small amounts together to get another 10 miles down the road.
Suggesting there's 2 liters of fuel below the lower petcock straw seems like a lot. Either you do have a bigger tank or it could be your lowest straw is significantly taller than most. There are no set dimensions but Snowbum has listed about 83mm for the tall straw and 23-24mm for the short straw.
Darryl Cainey
Sir Darby
Louie gave 3 different mileages there, you are thinking in American gallons.
The stock tank is 24L
The stock tank is 24L
mneblett
#32806
With or without the volume reduction from making more room under the tank in the later tanks?
pglaves
#13338
Like I said, I was guessin.
Take the tank off the bike. Empty it completely. Set it - level - on your work bench with the fuel taps accessible. Put the fuel taps to reserve. Be prepared to catch some fuel.
Add measured amounts of fuel in small quantities until fuel flows out of the petcocks on reserve. Now you know how much fuel is below reserve and won't flow out.
Switch the petcocks to on. Again add measured amounts of fuel until it just starts to flow out of the petcocks. Now you know the capacity of the reserve.
Turn the petcocks off and add measured quantities of fuel until the tank is full.
Now you know:
1. the absolute capacity of the tank,
2. the amount of the reserve,
3. the amount of fuel to reserve.
No more guessing. The whole thing might take an hour.
I updated article 1A on the website minutes ago. Clarified some details, etc.
http://bmwmotorcycletech.info/
http://bmwmotorcycletech.info/
