Forum bmwbike.com

At 2300 rpm , and only at this, ( yes , I have a rev counter on my bike) in the 3° gear , and asking for power, my right cylinder seems to detone and I can feel more vibrations.
Is this detonation possible?
Could that be rocket arms clearance ?
passing that rpm , the motor retuns running smooth and well.....
Mark, please , give me an advice.

Hi Michele,

I own a 1958 R50 and had a similar problem.

Areas to check are: Make sure you have good compression in both cylinders. Low pressure caused by a sticking ring, worn cylinder, etc. will give rough running, a lack of power and detonation.

Make sure the timing is spot on, both static and dynamic. Static at the 'S' mark, dynamic to the 'F' mark . As you know the advance/ retard unit can wear badly, the springs can break, the cam can seize on the mag rotor, so do check everything through. I made an adjustable bobweight stop to prevent too much advance and it works a treat.

Finally, be sure to balance your carbs with a vacuum gauge, this is the only way to get them accurate. Cheap but effective gauges are available. Check out the carbs for correct basic settings and as a precaution fit new jets exactly according to BMW. They know best!

I always use Bosch W4AC plugs, do the same.

I hope this helps.

Best wishes,

Gerry

I have a vacuum gage I find that electrode extenders work much better for adjusting and balancing carbs.

Could you be feeling a miss? A miss at low rpm under power can be caused by a bad spark plug cable or cap.

What relation between a vacuum gauge and electrode extenders ? can you explain your process for tuning the carbs ?

Two kinds of vacuum gages can be used on a /2. If the carb body is drilled and a tap is screwed in, you can use a mercury stick. This is how the later airheads are tuned - their vacuum carbs have a tap.
Or you can buy a dial gage that you hold over the carb intake. You remove the air tubes, and hold the gage on one side, then the other. There are several problems and disadvantages with this, which I can explain later.

Electrode extenders perform the same function as pulling off a spark plug cap, but you can do it instantly, on one side then the other, and it does not force the spark to jump the safety gap, so it preserves the coil. The electrode extenders are the best way to adjust and synchronize the carbs. I can explain the use of the electrode extenders, but I think I already did it one time here.