R65 carburation mixture adjustment.

[georgesgiralt]

Hello !
Since my bike can't get leaded 97 fuel any more, I need to adjust for European 95-E10 (with 10% ethanol).
I'm having trouble doing that. I always end with too rich a mixture at 3000~4000 RPM or too lean above 5000 or poor idle...
But I remember that someone on this forum has posted a chart explaining the influence of the various jets on fuel mixture depending on throttle opening. Alas I can't find it any more. I think this would help me understand and find the proper jetting for my bike !
So if someone has it I would be greatly indebted !
Many thanks in advance !

[Barry]

Is this the one you are thinking of.

[georgesgiralt]

Hello Barry,
No it was not this one, was easier to read and "more dumb user friendly". But I think this one will do fine.
As Bing carbs are concerned, I can't change the :
Needle diameter
Needle tapper
Unless the needle diameter is the needle jet diameter ?
I'm puzzled because the bike is wonderful at idle, I can go from idle up to 3000 RPM without any problem, whatever throttle opening I use. Then things become worse...
If I stabilize her at 3500 rpm, and open the throttle up fast, RPM goes down to 3000 before rising up again.
With the stock jetting, I can go like a bullet to the red zone.
Today with modified jetting, the behaviour I describe at around 3500 RPM is less present, but I can't easily go to the red zone, the bike seems to be too lean at 5000 trough 6000 rpm.
Last but not least, stock jetting gives me very poor mileage (6.7~ 6.9 l/km)
So I would like advices and a systematic approach to fine tune her. Hence my request for the diagram.
P.S. : Stock setting is Idle 45, main 145, needle jet 2,64, needle pos #4 soft springs.
Now I run the '83 settings : Idle 45, main 138, needle jet 2.66, needle pos #3, soft springs (I await the stronger springs)

[Barry]

For the purposes of interpreting the chart you can read needle diameter as needle jet diameter. It's the amount of fuel passing through the needle jet before the tapered part of the needle comes into effect.

Different needle tapers can be found but it's probably not a good idea to experiment as the stock settings shouldn't have been far off even with E10.

Starting with the stock settings I would change only one thing at a time rather than move from one years stock settings to another. For example it's near impossible to compare the difference between 2.64 needle jet and position 4 with 2.66 needle jet and position 3.

40 - 42mpg (imp) does suggest you are running rich somewhere so perhaps the smaller main jet will help. You could check the main jet size using this tuning guide for CV carbs which is one of the best. http://www.factorypro.com/tech/tech_tuning_procedures/tuning_carbtune,CV,lower_rpm_engines.html

[georgesgiralt]

Hello Barry,
Actually I did not explain myself properly.
At first I rebuild the carbs and renew all "brass" and rubber parts as they where 30 years old. I'll put new jets, new needle and new needle jets. New diaphragms and new springs, both throttle and choke and piston springs. (the choke was not closing fully because the springs had weakened... )
Then I rode the bike just to find that the spot between 3000 and 4000 was wrong. Seems too rich but I could be mistaken (RPM drop to 3000 and a bit lower when I suddenly open the throttle then the engine takes over and goes as wind... ).
So I tried to reduce a bit the main jet until I get to 138. The flat spot disappeared quite entirely but then the high RPM became bad.
So I thought I could install a bigger needle jet to compensate. Mixture began to become too rich also above 5000. So I decided to move one notch leaner on the needle.. Here I am, quite with the 83 settings.... But the journey was taken one step at a time. And the situation is not good. So I decided to cry for help and ask for a more technical approach...
The site you gave me seems to offer sound advice. I'll try their way of thinking after having returned the carbs to the factory settings.

[Bob_Roller]

By chance did you purchase 'pattern' not OEM diaphragms from Motobins or any other supplier ?

Members here have reported that the 'pattern' diaphragms from Motobins caused carb problems, don't recall what the exact issues were .

I think 'Lucky Lou' installed a set, so maybe he can fill in the details .

[Barry]

I rode the bike just to find that the spot between 3000 and 4000 was wrong. Seems too rich but I could be mistaken (RPM drop to 3000 and a bit lower when I suddenly open the throttle then the engine takes over and goes as wind... ).
So I tried to reduce a bit the main jet until I get to 138. The flat spot disappeared quite entirely

I think your too rich diagnosis was correct as the reduction in main jet will have had some effect on leaning out the mixture below 3/4 throttle.  But correcting the mid range with the main jet leaned out the top end so I would put the larger main jet back in and try to weaken the 3000 - 4000 range by dropping the needle one slot. It might take some experimentation with needle jets and needle positions but this is the right way to correct the mid range not by changing main jet sizes.

It's important to get the main jet correct first because all the fuel that passes though the needle jet has to go through the main jet and so a smaller main jet cannot leave the needle jet flow unaffected. As a result in spite of the main jet curve in the diagram showing little effect below 3/4 throttle my experience is that it has some effect all the way down to 3500 RPM and I think you have found the same.
 
It would be worth confirming the larger main jet size is correct  by carrying out the following test:

When cruising in 4th or 5th at 4500 RPM or more apply full throttle for a few seconds then roll off the throttle quickly to 7/8ths. If the engine pulls harder, the main jet is too small.  If it hesitates the main jet is too large.  If there is little or no difference in power the jet is near enough correct.

[georgesgiralt]

Thanks for your help, it's a relief.
The diaphragms are form BMW. The one installed are, I think, a bit old as the dealer had them in stock and with dust on the boxes.
I've  bought new one which should be at the dealer in a week or so. I'll see if they are as stiff than the one I own. (the original old ones where very supple, had no leak, so I was surprised when I got the new ones to see that the make has changed somewhat. (but I wonder if that makes any difference !)
It would be easy for me to swap the 138 main jet to the 145 and ride the bike at 2.66 jet needle and #3 position on the needle. It is the setting it has now. Just have to remove the bowl and swap main jet. Not a big deal !
So if the weather permits it, I should be able to experiment this very soon !

[georgesgiralt]

Played a bit this afternoon. Got to the highway with a set of jets and an 8 spanner in the pocket.
It appears that the main jet which gives the best high end response is the 145 (I did not try the 148 I forgot at home...)
Now, with the needle at position 3 and the needle jet at 2.66 she suffer between 4000 and 5000. Then she fly like a rocket up to the red zone.
So I guess I've got the main jet correct and I've to concentrate on needle and needle jet.
Will try this soon !

[georgesgiralt]

Found the picture I looked for !
It is near the bottom of this page :
http://www.stephenbottcher.net/BMW/jetting.htm

[Barry]

Yes that's a good one. I like the fact that it shows the straight section of the needle which you can read as "needle jet size".  

[georgesgiralt]

So this morning I had her with a needle clip in position 3 and a needle jet of 2.68. Seems to make a difference !
Looks like every clip position is worth 3 sizes in needle jet size.
(I went from a little too rich at position 4 and 2.64 to seems correct at position 3 and 2.68, the 2.66 being not enough)

[Barry]

Sounds like you are getting there.

The one clip position being worth 3 jet sizes has been reported many times.


It would still be interesting to do the calculations. I found a very old post on the airheads list that suggested the Bing manual contains data on needle dimensions or perhaps interprets the needle part codes.

Could some one with Bing manual have a look for me ?

It's supposed to be on page 27 although that might have changed. There are the BMW codes for the needle like 46-241 and Bings own code like 6H6 where the first digit indicates the tip diameter and the 2 digit indicates the needle taper length.


Anything like that in the Bing manual ?

[georgesgiralt]

Hello Barry,
I spent the lunch time circling around town. It was dry so best use it !
I'm a bit disappointed by my settings.
When hot she has a lot of tiny flat spots all around the place. The bike runs fine but, IMHO can run better. Not bad, though, it is miles better with the 2.68 than it was with the 2.66.
So I think this week end I'll restore the stock jetting and try your washer trick.
In the meantime, I'll try to put the stiffer springs to see if it changes something...