R80 G/S mileage question

[happy wanderer]

Hey all you R80 G/S owners out there. I rode my '81 G/S down to Salem from Vancouver BC and just calculated my mileage. I was getting from 32 to 36 mpg measured over 2,000 kms or so. (Yeah we went the long way round ;-P) The bike is low mileage as in less than 50,000 kms so far.

Is this typical?

It seems low to me for an 800cc bike but maybe I am being overly optimistic?

 

[globalrider]

Is this typical?

It seems low to me for an 800cc bike.

I get better mileage from my R100 GS and I know the R80 G/S gets better mileage than my R100 GS.

I get a consistent 45 to 50 MPG with my R100 GS with a few rare runs from the low 50s to 55 MPG. These numbers based on back roads riding at 100 to 120 km/hr.

 

[happy wanderer]

I get better mileage from my R100 GS and I know the R80 G/S gets better mileage than my R100 GS.

I'll check my fuel log files later and post.

Thanks GR.

I am thinking something must be wrong because Phil Hawksley's BMW specs page states mileages of 5.0 litres per 100 Km (at constant 90 Kph).

The rest of the spec data is totally confusing to me. It says / 47 mpg US or 56 mpg / 47 mpg US.
I think it must be 56 mpg for the UK (Imperial) gallon.

I do ride a little faster than 100 km/hr much of the time but even so, I am way off the mark at 32 to 36 mpg that is for sure.

 

[20774]

When you were cruising (uh, let's say legally), what was your RPM at say 65 or 70 mph? Depending on the final drive, you could be spinning higher which will result in poorer mileage. Specs show a 37/11 final drive. Some general calculations show 4800 RPM would be around 75 mph in 5th. By contrast, my /7 with a 3.0 rear drive is 4300 RPM and 75 mph.

 

[20774]

The rest of the spec data is totally confusing to me. It says / 47 mpg US or 56 mpg / 47 mpg US.
I think it must be 56 mpg for the UK (Imperial) gallon.

Correct...I just did the math and 56 is for Imperial gallons and 47 is for US gallons.

 

[happy wanderer]

When you were cruising (uh, let's say legally), what was your RPM at say 65 or 70 mph? Depending on the final drive, you could be spinning higher which will result in poorer mileage. Specs show a 37/11 final drive. Some general calculations show 4800 RPM would be around 75 mph in 5th. By contrast, my /7 with a 3.0 rear drive is 4300 RPM and 75 mph.

97 km/hr is 60 mph and if memory serves I am spinning around 4000 RPM. About 4200 RPM for 65 mph and closer to 4500 RPM for 70 mph. I doubt the tach is very accurate though. When I tuned the carbs using the Harmonizer which calculates RPM by counting intake pulses it showed it was off by over 100 RPM at idle.

 

[globalrider]

I am thinking something must be wrong because Phil Hawksley's BMW specs page states mileages of 5.0 litres per 100 Km (at constant 90 Kph).

That works out to 56 MPG IMP.

Even though my average on my R100 GS is 47.5 MPG IMP, I usually gas up at the 400 km mark. The best I have gone on a regular R100 GS gas tank was 449 km with 0.9 liters left in the tank (25 or 26 liter tank I believe).

My R80 G/S PD gas tank (32 liter tank I believe) should get me going at least 550 km with plenty of reserve remaining.

The rest of the spec data is totally confusing to me. It says / 47 mpg US or 56 mpg / 47 mpg US.
I think it must be 56 mpg for the UK (Imperial) gallon.

47 MPG US = 56 MPG IMP

 

[happy wanderer]

Correct...I just did the math and 56 is for Imperial gallons and 47 is for US gallons.

The line reads 5.0 litres 100 Km (at constant 90 Kph) / 47 mpg US or 56 mpg / 47 mpg US

I reckon he's got one too many 47 mpg's in there...

Also note it says Kph and not Kmh. What's that supposed to be.. Kilo Pascals per hour? Don't think so!

No mileage data in the original German or US owner's manuals.

 

[happy wanderer]

That works out to 56 MPG IMP.

Even though my average on my R100 GS is 47.5 MPG IMP, I usually gas up at the 400 km mark. The best I have gone on a regular R100 GS gas tank was 449 km with 0.9 liters left in the tank (25 or 26 liter tank I believe).

My R80 G/S PD gas tank (32 liter tank I believe) should get me going at least 550 km with plenty of reserve remaining.




47 MPG US = 56 MPG IMP

Thanks for your data. The original 19.5 liter tank was wanting a fillup at 240 kms so I put a R100 GS tank on it to get more distance out of a tank. It is 24 litres / 5.27 gal UK / 6.34 gal US.

Yep, something not right here. I did have a stuck oil ring last fall which I cleared by putting some trannsmission oil in the motor oil temporarily. Compression was fine after that little fix and the bike runs strong. Maybe the carbs need a good overhaul already. The PO said he put diaphragms in but I will need to go through them I suppose. Check compression again, plugs etc. also might be a good idea.
In another thread over in oilheads there is a guy whose front brakes were sticking causing horrible mileage. Hmmm.

 

[globalrider]

Thanks for your data.

I've been keeping a fuel log on MS Excel since I bought my 1990 R100 GS new in October 1991. At the bottom of my spread sheet column for MPG and l/100km, I'll have Min, Average and Max. Same for my R1150 GS Adventures.

It is 24 litres / 5.27 gal UK / 6.34 gal US.

Damn oil companies. No wonder they are stinkin' rich; their pumps are off. I put over 25 liters into that tank a couple of times and as much as 25.81 liters when dry.

 

[lkchris]

Don't think mileage achieved is unrealistic.

BMW R80s typically get poorer mileage than 100s. Too many revs. Rear drive of G/S is 3.56

It's also hard to find worse motorcycle aerodynamics than a G/S ... upright position, arms wide, big, high front fender.

Early R80 carbs were pretty rich and were leaned out in '85. Most of the time I can start mine cold with no choke.

In addition, published figures weren't with ethanol.

 

[globalrider]

BMW R80s typically get poorer mileage than 100s. Too many revs.

They do? Everything I read tells me I can get as much as 600 kms with my PD tank...that works out to 5l/100 or 56 MPG IMP...and I only got 55 MPG IMP once with my R100 GS.

I had an R65 for ten years and some of us know how much of a rever it is (short stroke motor - same crank as R45), yet it regularly got over 400 kms on a much smaller tank than my R100 GS.

Anyways, his gas mileage is way down.

 

[Woodgrain]

They do? Everything I read tells me I can get as much as 600 kms with my PD tank...that works out to 5l/100 or 56 MPG IMP...and I only got 55 MPG IMP once with my R100 GS.

I had an R65 for ten years and some of us know how much of a rever it is (short stroke motor - same crank as R45), yet it regularly got over 400 kms on a much smaller tank than my R100 GS.

Anyways, his gas mileage is way down.

I switch to reserve at around 200 kilometers on my '83 R80G/S and have for over 130,000 kms.I've had the bike since new. Ichris is on the right track.

Woodgrain

 

[globalrider]

I switch to reserve at around 200 kilometers on my '83 R80G/S.

I expect to get a lot more than that.

 

[happy wanderer]

Don't think mileage achieved is unrealistic.

BMW R80s typically get poorer mileage than 100s. Too many revs. Rear drive of G/S is 3.56

It's also hard to find worse motorcycle aerodynamics than a G/S ... upright position, arms wide, big, high front fender.

Early R80 carbs were pretty rich and were leaned out in '85. Most of the time I can start mine cold with no choke.

In addition, published figures weren't with ethanol.

Thx Chris, All good points. I have certainly noticed higher revs at typical highway speeds than those of my RS which eats up miles like candy. Both these bikes were built in 1981, the G/S in March and the RS in July so the RS is registered as an 82. Have never really tested the mileage of the RS but it seemed reasonable when traveling with other airheads.

Your comment about starting cold fits exactly with my experience also. I reach for the choke all the time by habit but it starts with it off most of the time other than much colder days. Even then I can almost immediately turn the choke off and just advance the throttle a wee bit and it will run smooth. So it must be running fairly rich from the get go.

Still though, 32 to 36 mpg seems very low.

 

[PAS]

This may be of interest, http://bmwmotorcycletech.info/R80-fuel-mileage-problems.htm

 

[sdpc2]

I'd like to know how you folks are getting such good guel mileage

I had my GSPD for 4 years and about 30k miles, and averaged mid 30's for US MPG. No where NEAR 50....

 

[cycleman2]

Don't think mileage achieved is unrealistic.

BMW R80s typically get poorer mileage than 100s. Too many revs. Rear drive of G/S is 3.56

It's also hard to find worse motorcycle aerodynamics than a G/S ... upright position, arms wide, big, high front fender.

Early R80 carbs were pretty rich and were leaned out in '85. Most of the time I can start mine cold with no choke.

In addition, published figures weren't with ethanol.

Good answer.

Check the color of spark plugs and it will tell you if you are running rich or not. Also make sure the choke goes all the way off, they can stick on slightly which will affect your gas mileage.

 

[globalrider]

Also make sure the choke goes all the way off, they can stick on slightly which will affect your gas mileage.

Standard practice for me is to confirm that the levers are at their stop after I switch the choke off and I stop at the next light or intersection. A tired old rusty return spring doen't help either.

 

[happy wanderer]

This may be of interest, http://bmwmotorcycletech.info/R80-fuel-mileage-problems.htm

Snobums' article is interesting. I don't really understand the physics of the four holes at the front of the snorkels but it prompted me to take a look at mine. The bike I have was bought in Austria and built in March 1981. So not an 80 but anyway the snorkels are plastic and appear to be of equal length as I peer under the tank. There are no holes in them.

I made some erroneous RPM comments earlier. On a freeway ride the other day I noted that the engine is turning 4500 RPM at 60mph and 5300 RPM at 70mph. With a red line of 7000 that is pretty high revs. I recall reading here that when airhead motors of any kind start turning more than 4000 RPM fuel consumption increases fairly dramatically. I've tried putting around at 55mph and some days and on some roads that is just nice but the bike is very smooth and just so much fun to ride that sooner or later I'm moving somewhat quicker.