Fuel consumption?

[Mainerider]

So I've been loving riding my R65 but I was a little disapointed when I calculated my fuel consumption and it's just over 30 MPG. My '82 Honda Nighthawk gets over 40. Maybe I'm just spoiled by the 100+ MPG I get on My SYM Symba.
So what kind of gas mileage do you guys get?


Steven

[nhmaf]

Mid 40s is typical, I've gotten as high as 51MPG, but usually it is around 46-47 assuming that I am riding reasonably smooth and no more than +5 MPH over the speed limits.  If you are just making alot of short ~2 mile trips around town, it will be worse.

If you hear from the Brits - they will get even higher MPG numbers of course because their British Imperial Gallon is more than our wimpy American Gallon.


Also, if your carbs aren't setup right, or you've got some Mikunis on there, your mileage will be lower and running rich.    What do your spark plugs look like?

~30 MPG is about what you can expect to get on the R65 if it is dragging a sidecar along.

[Barry]

If you hear from the Brits - they will get even higher MPG numbers of course because their British Imperial Gallon is more than our wimpy American Gallon.

I would have to flog mine to get it below 60MPG Imp  (50 MPG US) My average this year is 66 MPG Imp  (55 MPG US) Besides the bigger gallons we have the small advantage of less ethanol in the fuel and possibly higher compression engines.

Lots of things you can do to improve consumption. Start with the carbs as just over 30 MPG US means there is something wrong with them. I would check float levels, wear on the needle jets and my old hobby horse properly set (not overly rich) idle mixture settings which have a significant impact on consumption in moderate use given the idle circuit is still making a big contribution at up to 1/4 throttle. On my back road cruising at 50mph I'm using only 1/8 throttle so it really does make a difference. I'm not talking excessively weak to the point where it affects performance as that doesn't work. Best performance and efficiency go hand in hand.

I also use thinner semi synthetic 10W40 in the engine and semi synthetic throughout the transmission which all helps a little to reduce drag. The whole airhead transmission has bigger losses than a chain driven bike where the gearbox is running in much hotter engine oil. Our bikes take longer to warm the transmission oils and never get to engine temperatures so the oil drag is particularly higher when cold.

Try this little experiment. Spin the back wheel by hand when cold and do the same when you get back from a ride. The difference in oil drag is huge. Now try the same thing on a chain driven bike.

[Luca]

I'm getting about 43mpg out of my LS with combined city and highway riding.  I'm pretty liberal with the throttle both in town and on the freeway though.  When passing (especially trucks) on the freeway I usually approach at cruising speed and try to stay in the driver's mirrors... and then when close whack it wide open to get ahead of said vehicle.

Rider/luggage weight it a factor too.  At about 230 pounds geared up I don't expect to get as good mileage as the test riders.  My front brakes also drag a bit and aren't helping.

[Matt Chapter]

Last time I checked I was getting low 30s in US mpg.. but that was before the transmission rebuild.  I'm very, what's the word, open to using the throttle.. and my speedo is busted too.

[Luca]

Also, if your plugs come up looking OK I'd make sure that your odometer is working.  Plan a route on google maps and see how your meters match up to the calculated distance.

Two other things than can hurt mileage are lots of hills and consistent wind.

The factory manual says BMW's German DIN 70030 standard for measuring fuel consumption requires that the bike be up to temp and ridden on a course with no more than 1.5% grade and wind not exceeding 6.7mph and loaded halfway between unladen and gross weight.  Speed should be 3/4 of top speed but not exceed 68mph and be as uniform as possible, and tires should be of correct size and properly inflated.  Oh, and no brake drag allowed.

Under those ideal circumstances (without ethanol in the gas) the manual says machine should get 51.1 mpg.  They say to allow a 10% deviation for unfavorable circumstances... go figure

[Barry]

The factory manual says BMW's German DIN 70030 standard for measuring fuel consumption requires that the bike be up to temp and ridden on a course with no more than 1.5% grade and wind not exceeding 6.7mph and loaded halfway between unladen and gross weight.Speed should be 3/4 of top speed but not exceed 68mph and be as uniform as possible, and tires should be of correct size and properly inflated.Oh, and no brake drag allowed.

So that's what the figures in the riders manual are based on. At least it's a benchmark so that if you ride moderately as described and don't achieve the prescribed consumption it's a good indication that there is something amiss with the bike.  The figure for mine is 62.8 Imp (52.3 US)  I can achieve that figure ridden like that.

[Mainerider]

Sounds like I have some work to do. That 30 MPG was riding to the Downeast Rally. 10 miles on the interstate, the rest on secondary roads going 50 - 55. Not many hills. I did have some luggage and camping gear.  Maybe another test run this weekend.



Steven

[Bob_Roller]

I've had my '81 R65 since January, '81 .
I lived in the Chicago area at the time and 5% ethanol was in the fuel supply .
I averaged 45 mpg then, speed limits on the rural highways was 55 mph, I could squeeze an occasional 50-52 mpg, with all interstate highway  type riding for a full tank .
I moved to Phoenix in October, '93, there was MTBE in the fuel instead of ethanol, I was getting a consistent 45 -50 mpg then, still 55 mph highway speeds .
10% ethanol was added to the fuel supply and speed limit increased to 75 mph on rural highways about 12 years ago, fuel consumption is now at 38-40 mpg, I hit reserve around 190-200 miles now .
Increased speed and alcohol don't make a good combination for fuel consumption .
I even replaced the main jets on the '81 R65, from 143, to I think 135 or 137 and saw no difference in fuel usage .
Get alcohol out of the fuel, and back into beer, where it belongs !!!!!!!!!!!
My first suggestion, would be to replace the needle jet, it takes a beating from the needle .
Check the float level and condition of the float needle valve, it has a rubber tip and gets hardened with age .
Then a full carb synchronization .

[nhmaf]

BUT FIRST - make sure that the valve lash is properly set before messing with the carbs!

[davidpdx]

I changed out my throttle cables recently and did not do a carburetor balance. I dropped my mileage from the high 40s into the 30s for in town riding. Did a careful carb balance and got close to 50 on the last tank. I would not have believed it could make that much difference if I had not seen it for my self.    

[Barry]

I changed out my throttle cables recently and did not do a carburetor balance. I dropped my mileage from the high 40s into the 30s for in town riding. Did a careful carb balance and got close to 50 on the last tank. I would not have believed it could make that much difference if I had not seen it for my self.  

That is a surprising difference. With out of balance carbs one cylinder is dragging the other one along. The one being dragged will run weak and the one doing the dragging will run rich and neither will be running efficiently.

[Mainerider]

I have an airline pilot friend who lives in Georgia and said he would help me sync my carbs. I'm waiting for him to have a layover in Portland. He owned an R100 for years and told me he'd teach me how to do it.
Latest fill-up was 32MPG

[Tony Smith]

Latest fill-up was 32MPG

In my experience one of the most often overlooked things that can greatly increase the amount of fuel you use is the condition of the carbs generally.

Unless something happens to block them up solid, you simply do not notice the slow deterioration in mileage and performance as carbs wear out.
 
The newest R65 is long past the date where the carb internals should have been completely renewed, especially the floats, float needle and seat, main jet and main jet needle.
 
Caveat, Snowbums article says several times to not us Stromberg diaphrams and also mentions Bing USA in less than supportive tones.
 
Aside from buying a manual from them I have never bought anything from Bing USA, but I find it incomprehensible that BING would manufacture the same parts to two different engineering standards, in fact given that BING USA's (and indeed BING worldwide, main interest is in making and supporting aircraft carbs, the idea of multi-standard replacement part manufacture is up there with "we didn't land on the moon" or "the government has been taken over by aliens". Not I hasten to say that I want to detract from the rest of Snowbum's article, which is 1st class.

The other small difference of opinion I have with him is that I have been using Stromberg diaphragms since around 1983 and am yet to have a problem with one, noting that on average they cost less than one third of the BMW variety.
 

[Mainerider]

The previous owner of my bike had the carbs rebuilt at a shop a couple of years ago. I'd need to check the receipt but I know it had new jets.
Interestingly the Danish motor I have in my sailboat, a Vire 12, has a Bing carburator.