Carburetor experiment

[georgesgiralt]

Hello Gals and Lads !
I own an '82 R65  (I'm the first owner...) and also the factory manual with the updates up to 1985.
I can't use less than 6,1 l/100 km of European 95 or 98 gasoline.
So some time ago I started wondering if BMW had done something to improve this situation.
I started looking at the factory manual and saw that they changed the jetting in 1982 and another time in 1983.
So I decided to try the '83 setting. But this involve exchanging the air filter cap and the springs in the carbs in addition to the jetting.
initially I had a 145 main jet and a 2.64 needle jet with the needle in 4th notch. Soft springs and  symmetrical   air filter cap (the one with two  identical tubes).
Today I installed the "new" filter cap with one large  and one small "trumpets", then I put the  stiffer springs , put the  needle in 3rd position and replaced  the main jet to go  to 138.
I  don't  know if it is real or not but it seems the bike  runs better at every throttle position. There is not he flat spot around 3000~4000 RPM and she want to go fast !
It is too early to see if I improved gas usage but we will see !
If you are interested I can compile the various jetting and part numbers needed. (I wonder if these settings are valid in the USA or Australia ?)
All in all I'm an happy customer !  Tomorrow morning, washing time for the bike and extensive test on small roads around my town.

[Bob_Roller]

I experimented with different jet sizes with my '81 R65, it had 145 main jets from the factory, I got numerous different sizes with the spare parts when I got my '84 LS and saw no difference in fuel consumption or engine performance .

10% ethanol has been in the fuel here, for about 12 years, that alone cost me a 13% loss in fuel economy .

Before ethanol, I could get 46 miles per US gallon, 5 liters per 100 km, now I get 39 miles per US gallon, 5.7 liters per 100 km .

Your 6.1l/100km is a bit high for an R65 .

Have you replaced the needle jet

How accurate is the odometer

[nhmaf]

I'll have to check the numbers on my 82 LS carbs, which are still stock as far as jets and needles go.   I seem to recall talking to a number of airheads a few years back and we had generally agreed that the 138 were the best size to use with the stock airbox.   My airbox has the asymmetric nostrils, too

[georgesgiralt]

Hello Bob,
In 2013, I refurbished  the two Bing completely. A thorough cleaning,  all new rubber and all new brass.
It was funny comparing the old needle to the new one...
At one time I tried to dial in the jets for the 10% ethanol fuel we have in Europe. I was able to make the bike running quite fine but the gas usage was terrible ! (above 7.5L/100 km) It was offsetting more than twice the lower cost of this fuel ....
in France (and I guess in Europe) all fuel include up to 5% ethanol, 95-E10 is at 10 % and E85 is at ... 85 % ethanol. I run 98 rated fuel in the R65 and if not avail, 95 rated.
As far as I know, my odometer is  fine. I live in a "big" city (4 or 5th in France). So I've to ride quite a lot in the city before reaching either small roads or the highway.
This morning I tried to run the bike hard at high speed and high load. The 138 main jet seems  a little too small. If I can, I'll try a 140. 

[Bob_Roller]

I've had the 138 size jets installed for 4 years with a 2.66 needle and bike runs no differently, than when I had the stock 145's installed .

If you have a lot of city riding, that's going to have a negative effect on fuel comsumption .

[georgesgiralt]

Bob, I use the 2.64 needle jet and 3rd position for the needle.
She is running quite fine. Will see what the gas mileage is.

[mrclubike]

Thank you George for starting this thread
It is very good information to help me sort out my flat spot between 4k and 5k rpm

In case some searches into this thread and wants to read my thread
just search for the thread titled
"Flat throttle response and surging below 50f"