Forum bmwbike.com

My question isthis : When BMW went to the large non-choke air filters on the R50/2
late in the '60's, did they change any of the the carb jet sizes from what they were
using previously? I wouldn't want to run too lean and burn a hole in my piston.
Similarly, I wouldn't want to run too rich and lose all gas economy.

Does anyone know the answer?

This may not be the answer you want. The Bing catalog lists such things as jet sizes, needles and settings. They vary by the Bing carb number.

The carb number is toward the outside between the flange and the slide. There are several different carb numbers for R50/2. The differences seem to be in the slide, and not in the jets or needles.

I see nothing in the catalog about air filters. It appears that the type of filter is not something that affected Bing.

Hallo J.,
BMW had changed the jet(Hauptduese) in dependence with the airfilter.Do you have the last edition?there are 2 types with paper airfilter.If you answer me I will look at home and send you the jet size.On the other hand,you have always try to find out the best
size by the the highest speed you can achieve with this jetsize(normally, you must take one number[ f.e. 105 to 110]higher as wriiten by BMW.Never the less, if you write me your airfilter"edition", I will sent you the BMW jet size.It could be helpful to sent me your carb-numbers.
Rolf

Carb No and Main Jet Size for R50/2
1/24/45-46 is 105
1/24/131-132 is 105
1/24/145-146 is 105
1/24/149-150 is 120

I think you have answered my question. I have "upgraded" my bike to the post
1967 large non-choke airfilter housing and Microstar filter. These were previously
used only on the "S" bikes, but after August 1967, BMW standardized.

I was hoping to get a little more umph out of the bike. Knowing the jet sizes is
a big help.

So in conclusion, even though my carbs originally took 105 jets, it looks like they
should now take 120s


Thanks.

Hi , I think you can get the answer in the site
www.beemergarage.com (BMW bulletins) , looking for the service bulletin JUNE 1968.
this bulletin talks of the main jet setting when changing the carbs or teh choke / non-choke air filter.
I have the paper choke air fiter (that one shown on the R60 in the front cover of the R. Slabon book How to restore your ..... etc), I have also the 1/24/149 -150 carbs (/2 kind) which should mount the 120 main jet; with the non choke air filter, and, if I am not wrong from the service bulletin, the 125 main jet if you have the choke air filter I have.

Let me know your thought.
Michele

dear friend,
I have a R50 1960 (not a /2 , but one of the last R50s) , with the following items on it:
Paper (micromic) Air filter with sliding choke (old BMW Number 0043033)
Carburators 1/24/149 - 150 with main jet 120
(BMW N° 13 11 0 039 073 / 4)

Is this combination correct ? do I need to change the main jet ?

thanks

hallo michele,
you have the latest edition of Bing carbs(for the latest airfilter, without choke), the only difference is the the mainjet size, for all(!) the older types of airfilter Bing and BMW prescribes mainjet 105.Normally the prescribed mainjet are too little, because BMW tried to get a minor consumption of fuel(it looks good in the advertisings).I think you will need a 110 or 115 mainjet, you have to try the best combination(best highspeed,acceleration , color of sparkplug and so on).your jetneedle(?) should be on position 3 by mainjet 105. It could be better using position 2 or 1 when you take mainjet 110 or 115(see above).
rolf