Fuel consumption

[bangpaul]

I've worked out that my bike is doing about 14 kms to a litre. I know these bikes are far from efficient, but that still seems a bit rich. Is this normal? How can I improve efficiency?

[Dizerens5]

My 79 is doing exactly the same. It's not ideal.

[Barry]

That's roughly 40 mpg (UK) which doesn't seem very good to me unless you are flat out all the time.

I average 64 MPG overall and have been regularly hitting a best of 70 mpg this summer and although I have a smaller engine there is almost no difference R45 vs R65 in the official fuel consumption figures.

Besides the usual issues of correct float levels and unworn needles and jets, my secret for good fuel consumption is to tune the idle mixture screws properly with a hot engine. That means turn them in till it stumbles and out again only enough for smooth running which is likely a screwdriver width - none of this "and another 1/4 turn out" nonsense that you may read about.  Although I've never read it I believe the Bing manual advocates a trial and error method of ride and adjust leaner to achieve the best possible idle mixture. The idle mixture setting has a much bigger impact on overall fuel consumption than most people imagine. This is because the majority of the time we only use 1/8 to 1/4 throttle where the idle circuits still have a big influence. This has worked for me to achieve 60+ MPG on every bike I've had in the last 40 years with one exception and that was a Z900 which had no earthly hope of getting near that figure.

[Bob_Roller]

The final drive ratio is a main cause for the not so great fuel consumption .

The 1000cc bikes of the same era get about the same or a little better than the R65 .

You can try different jets and what not, but it won't result in much better fuel consumption, I've tried it .

[Justin B.]

I flog the Dawg pretty hard and get right around 40 miles per US gal.

[tvrla]

Thanks Barry, interesting advice!

I'd imagine with fuel consumption like that you ride conservatively? And you haven't geared the bike taller?

That's one thing I've heard - the R65 can handle 3.20 gearing just fine.

My beemers tend to get anywhere from 40 - 50 mpg, but I'll have to try your trick and see what happens.

[Bob_Roller]

I don't know if you noticed his signiture, Barry has an R45, not an R65 .

[Barry]

I'd imagine with fuel consumption like that you ride conservatively? And you haven't geared the bike taller?

My figures are UK gallons so they will be approx. 20% higher than US gallons. Also in the UK we have only 5% of the evil ethanol in our fuel so far which may make a few % difference.

I get 70 MPG riding quiet country lanes at typical 50 - 55 MPH maybe occasional 60 MPH so that means I'm not exceeding 4500 RPM.
I don't often ride or enjoy 70 MPH type highways but even then I get 60- 65 MPG.

My R45 is not geared taller in fact quite the opposite I'm revving more than any R65.  The carbs are 28mm so maybe a bit more efficient than the 32's at small throttle openings. Although the BMW official consumption figures in the riders handbook are very little different R45 to R65 I think that's based on 62 MPH. I probably do better than an R65 at lower speeds. .

60 MPG should be easily in reach of an R65. I'm sure Lou got that figure recently.

[tvrla]

Thanks for that Barry - makes for a better base to compare.

My last fill up (today) took 4.4 gallons (though I did fill it higher than usual - normally I fill to the bottom of the filler neck, this time to the hole half way up) and I went 215 miles for 49mpg.

My bike's far from stock though - with the CC products 850 kit, head work, 34mm flat slide Mikunis, and a taller 3.36 final drive. This is a combination of highway and backroads riding. On the highway (in town) it's 55 to 65 and 35 to 45 in town.

So let's see - to convert to UK mileage I'd need to multiply that by 20% which gives about 60, and then there's the alcohol to factor in as well. I guess I'm not too far behind you.

[Barry]

I calculate consumption measured from reserve to reserve which I think should be fairly accurate and repeatable. I note the mileage when the bike goes on reserve and typically add 15 litres. I have a record of all fuel used. There is a very obvious winter summer cycle due to cold starts and short commutes in the winter and it's interesting to see how average consumption has improved  from roughly 60 to 65 MPG over the last 4 years as I have gradually dialed in the carbs. Looking at the poor result in 2007 I can cross check with my service records and the big improvement the following year resulted from cleaning out a clogged emulsion tube on the LH carb.   

[clonmore1]

Interesting stuff Barry,

I am sure that Lucky Lou said recently he was getting circa 60mpg. I shall be checking mine as I build the history of the bike once it is back on the road.

Chris

[RSMike]

I have not actually scientifically checked mine, but I have a feeling its pretty bad, I'm sure my carbs could be tuned better, but as the bike runs and feels well, I'm loath to go messing.

Probably come winter I will do a carb rebuilds and work on a good tune after that.

[Crossrodes]

Last time I checked mine I got 64 mpg on an Imperial Gallon.  That would equate to approximately 43 mpg in US gallons.

[clonmore1]

According to the BMW brochure of 1981, the fuel consumption of the 65 is 61.4 imp gal.

[Air4Life]

Roughly 45 MPG '83 mix riding.   I've done nothing to the metering.

[size=8]1983 R65 Monmouth County, NJ[/size]