Forum bmwbike.com

I have had my R27 for 30 years, although it has been in storage for the last 5 until just recently. I have cleaned out the carby and blown out the jets and find that:
It is very hard to start and the revs take a while to die down after blipping the throtle, or the revs start to increase from idle and the engine starts to race even though the throttle has not been touched or the cable accidently pulled by turning the handle bars. I remember this as a problem before I stored the bike, in fact it was probably why I put it into storage in the first place.

The Bing carburetor has the markings 1/26/68. I remember fitting an accelerator pump, which was recommended at the time I bought the bike. I also remember adding some solder around the centre of the float to increase its mass. Apart from that it has not had anything changed, although a new slide and jets were purchased and installed several years ago.
My questions are as follows:
Does this sound like a carby problem or should I look at the coil and the advance unit? - the timing is OK.
Was the addition of solder around the perimeter of the middle of the float a reasonable thing to do to increase its mass (the new weight is 11 g and was 7 g -this is the spec given in the Clymer manual), or does the heavier float have the float needle catch in a different position?

Can anyone explain the revving symptoms I have described?

I don't know of any other owners of R27s in Australia so I would be very grateful for any suggestions anyone may have. Thank you for your help.

Hello Holger,

I think you are on the right track in diagnosing your problem. I would first completely rebuild the carburetor, cleaning out all the internal passageways, and I'd replace the float with a correct unmodified part. I've never heard of adding weight to a float, and I would expect this to cause the needle valve to stay open all the time, causing a flooding problem. Even small float weight differences can cause problems with maintaining a correct fuel level, and you've added a LOT of weight. I'd get the carburetor right before starting on the ignition.

Regarding the advance unit, I had a similar problem with my R26 not wanting to return to idle. I found that a new advance unit solved the problem. The original advance was worn out and didn't move smoothly, and the springs were stretched, allowing the ignition to advance too rapidly and stay advanced too long. This can also contribute to hard starting. You can observe your advance mechanism in action by watching the timing marks with a strobe light while revving the engine.

Regarding the coil, if yours hasn't failed it eventually will. The best insurance is to have Mark Huggett rebuild your original coil, or replace it with a new German coil. Most of the reproduction coils on the market are junk. I'd also recommend replacing your condensor and carrying a spare with you, because they are the weak link in these ignition systems. Also be sure you have a non-resistor spark plug cap.

Good luck and let us know if you solve your problems.

Dave

I do not know what float is in my R27, but I do know that my R60/2 has 7-gram floats. Also, the following is copied from the Huggett catalog:
   13 11 0 039 186  Bing float 11gr (35-073) R24 - R25/3; R27        
   13 11 0 039 187  Bing Float 7gr (35-072) 
It sounds like the R27 uses 11 grams and the twins use 7 grams, and that is why weight was added to the 7-gram float in this person's R27.

Hello Dave,
Thanks for your reply. I've ordered some parts from Mark, so hopefully this will solve my problems.
The T-122 Bing exploded parts diagram gives the parts number of the 11 gm float bowl, but for the carby model without the accelerator pump. The Clymer manual lists the 7 gm float for carbies without the accelerator pump and 11 gm for later models with the pump. There appears to be a contradiction between the two. Also, the rubber connection tube between the air box and the carby is supposed to have a hole at the bottom, according to a BMW service bulletin, presumably to counter any flooding from the heavier float - mine was a bit of rubber tube which wasn't perforated.
My automatic advance unit wasn't returning correctly as you suggested - one of the springs appears stretched. I will replace the springs first to see what difference this makes before forking out for a new unit.
Holger.