Type of carburators for BMW R51/2

[Goro F]

Hello
i've fixed all leaking point of my carburators.

Now I found this table where is mentioned the types of Bing mounted on R51/2 and the relavant set up / parts

On my bike are mounted 1/22/61 Left and 1/22/62 Right and I noticed that the main jet is 85 (as shown in the picture i share)

I do not find these types of carburators in the list and i also see that 85 main jet is never used.

Anybody can tell me which main jet i should choose for my carb (or 85 are the right ones?) and on which model of bikes were used 1/22/61 and 62?

[schrader7032]

The Bing manual only shows the 1/22/39 and /40 carbs for the R51/2. Suggests main jet of 90. The 61/62 are for the R51/3.

[Seek]

The number just indicates the setup as sold from Bing. It is the same carburettor with different jets. So I would use the settings from the manual.

[schrader7032]

The slide is a critical element to the functioning of a carb. Slides have different shapes and ports on them. So, mixing and matching jets should take into account the basic similarity of the slides.

[R68]

..22mm Bings are hard to find; your lucky to have them. If the float bowls are rotted out they can be repaired; if the flanges are warped they can be trued..although expensive, wear parts, slide needles, jets, etc. can be replaced...

[808Airhead]

Yes, you have the later carbs for R51/3. I have a early R51/3 which came with the same carbs you have,the incorrect, later ones. This early 1951 came originally with the same 39/40 carbs found on R51/2, so the search was on, and found a nice set of 39/40 out of Europe. They are rare, so if you want the correct carburetor, make sure you snatch them up if you come across a set. These cost me $1200.00 6-7 years ago and were mint, EXCEPT for the main jet seat which cracked apart rendering one carb useless, which was a terrible situation, I went in there and welded it up and reshaped it with a pencil grinder and voila! It’s been perfect ever since… good luck !!

[Bmw1950-1969]

1/22/29 and 30 also is for a 51/2. I may have 1/22/39 if you are interested.
Bill

[Goro F]

thanks all for replies and informations

i will try 90 and 100 both, accordingly to the other setting, and listen how the engine runs. (105 seems to be the reccomended one in case of side car)

questions for carburator setting: this procedure is also valid for my bike, i assume. Am I wrong or shall i take some specific attentions?

I seriously hate the practice of balancing the two cylinders by pulling the plug wire. It is crude and in my opinion is not the best way to perform this task.

I have used the procedure as highlighted at Duane Ausherman's website available at https://w6rec.com/adjusting-the-2-bing-carbs/ under the "BMW motorcycle carb tuning procedures, by ear" section. It works VERY well and is quite exact.

My crib notes are below, but you really should read Duane's full writeup as its very detailed and good.

1) Start with both air screws at the suggested setting (1 turn or 1-1/2 turns out)
2) Turn the left carb idle screw in 1/4 of a turn to increase the idle slightly.
3) Turn the right carb idle screw out slowly until the motor is almost ready to die and then go back in 1/8-1/4 turn until it a consistent, but very low idle.
4) Turn the left carb air screw in and out until you find the locations where the motor runs rough and then adjust the air screw roughly 1/2 between the two points and then turn a bit more in (1/8 turn in). This richens the mixture to help get the motor to rev off idle easier.
5) Turn the right side (the other side) idle screw back up and the left one down repeating #1-#3 above but reversed.
6) Repeat step #4 above but for the right carb.
7) Bring the idle screws back to where you think they should be.
8) Get on the floor behind the motorcycle and listen to both sides. You will be able to clearly hear one side that is stronger than the other. Adjust the idle screws so both side are the same. I have found that using a piece of cardboard to block the sound of one side helps fine tune it.
9) Adjust the throttle cables so they have the SAME free play on both sides. This is important to ensure the slides are pulling at the same time!
10) Go for a ride and enjoy.

I can guarantee that Duane's method works wonders and will let you find out if you have a bad side. I have been able to debug dirt in the carb by getting on the floor behind the motorcycle and listening. It looks strange but it works.

By the way, my motorcycles tuned using this method will idle all day long on one cylinder beautifully. You almost don't know the one cylinder is not firing!

Good luck!!!

James

[Goro F]

i will try 90 and 100 both, accordingly to the other setting, and listen how the engine runs. (105 seems to be the reccomended one in case of side car)

errata corrige: with carburators types 1/22/61-62 no diffences for "solo" or "side car". 105 in both cases