Carburettor adjustment for BMW R75                                      H-P Hommes                                                                   

You have to synchronize the engine to make it run smoothly. An absolute requirement for this is a mechanically perfect condition of the carburettor and the correct equipment of carburettor jets. The following items  have to be controlled:

                                 -         Clearance of the carburettor slide  in the housing 0.02-0.06 mm

-         Float and carburettor piston needle undamaged

-         All jet ports clean and in the right size

-         Original equipment of jets

-         No damage on housing

-         The surface where you put the screws has to be absolutely flat

Today it is nearly impossible to get well overhauled Graetzin carburettors. Nowadays you can get carburettors from new production. Visually they look just like the original, but you have to change the carburettor jets and adjustments..

Spare parts for BMW R75 Hans-Peter Hommes Kamphausen 170  D-41363 Jüchen Germany Fax +49 21 66  606670


The basic adjustment of the idling speed ( Do not let the engine run )

- Turn the screws of the accelerator cables completely into the carburettor cover

- Turn the air regulation screw as far as it will go and then 1.5 turns back again 

-Turn out the carburettor slide adjustment screws until the slides are completely

  closed, turn the screw back in again until they touch the carburettor slide and now  further turn

- Start the engine and let it warm up.

- Remove the spark plug connector and turn the air screw as long as the working cylinder is

  true running  and has reached its highest speed

- Repeat the adjustment with the other cylinder

- Put back the spark plug connector

 - The synchronisation of both carburettors is done with the carburettor slide adjustment slide screw. By turning it in or out both carburettors will become homogeneous and the idle speed is achieved. To do this you need a lot of feeling and good hearing.

-Adjust the clearance of the accelerator cables with the tuning screws at the carburettor covers to 0.5 mm

- Accelerate briefly, the engine  should not splutter and swallow

    If the exhaust smoke is soot-black the mixture is too rich: Turn the air regulation screw out.

     If the engine splutters or swallows the  mixture is probably not rich enough.

    You can remedy the matter by turning the air regulation screw further in and you put the piston needle higher.

 If you have taken the above action and you have still not achieved a perfect idling speed then you have to control the adjustment of the engine (clearance of valves, valve timing, ignition).

 This translation is out of the book        Wehrmachtsgespanne gestern und heute          von H-P Hommes ã 1997