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Got my 74 R90/6 running this weekend. Gunk in the jets and the floats were too high, think they were bottoming out on the base and not closing hard enough. Plugs were bad, put a used set of NGK in there, fired right up. The ignition key positions are a bit confusing, what is the difference of position 3 and 4 as the ignition lights up, I do see the tail light operate in 4 and headlights in 5.

Got it warm and took a compression test when warm. Not wonderful. Just around 110 in each cylinder. Book is in KG but I figure I am in the area of poor to just below normal. Figure I may have to rebuild the motor. So what is the consensus, have a pro do it. Do it myself ( I do have extensive mechanical experience) and farm out processes like valves and boring?

The bike starts easily, no smoke, no leaks, everything appears to be original, including the tranny. I did find one obnomily on one carburator, just couldn't find a wrench to fit the nut on the choke lever, tried everything in metric and 'merican, turned out someone sneaked a whitworth nut on there Luckily I do have English iron and a supply of those wrenches.

Whats the trick on getting the tubes back onto the air cleaner snouts, haven't learned the BMW secret yet. Thought about removing the stop tabs on the tubes, but then the hose has a step in it, so that was out.

thanks,

gg

jagarra wrote:Whats the trick on getting the tubes back onto the air cleaner snouts, haven't learned the BMW secret yet. Thought about removing the stop tabs on the tubes, but then the hose has a step in it, so that was out.

The trick is to loosen the clamps holding the carb on the head side. With the rest of the clamps loose on the air tube, you can then maneuver the carb and tube much easier to make the connection. Then slide everything back in place and tighten the clamps. Note: that the air tubes are handed...they go on one side and one side only. It has to do with the offset spacing of the cylinders and thus the carbs.

Kurt in S.A.

Did you do the compression test with the carbs off - or at least with the slides blocked open and the throttle open?

If not, then your compression is actually higher than the measurements you got. Just holding open the throttle on CV carbs is not enough.

On the compression test I removed the left carb as in the picture in my service manual and held the throttle wide open. Hope that was correct.

gg

jagarra wrote:On the compression test I removed the left carb as in the picture in my service manual and held the throttle wide open. Hope that was correct.

gg

Uhm, if you only removed the left carb, then, no, that would not give you an accurate reading when you checked the right side. If you always removed the carb on the side you were testing, then you're fine.

jagarra wrote:On the compression test I removed the left carb as in the picture in my service manual and held the throttle wide open. Hope that was correct.

gg

If you remove the carb, you don't need to hold the throttle open.

I guess it goes without saying that you want a good, strong battery for the compression test?

It is important to count the compressions while watching the gauge. The way the compression increases is indicative.

OK, I will do it over with both carbs removed. Funny how the official service manual neglects to mention that. Ordered a bunch of stuff for it to replace all the flackey items, carbs kits, new plug wires, all the ducting for the air cleaner and a replacement for that whitworth nut. Also got new steering head bearings, these are so clunky it is hard to turn the thing, it would be a real handful on the road. After I replace all those items, I guess I will license it and start using it to check out what else is wrong. The turn signals light up, but they don't blink, unusual to have the switch on the right side, will take a while to get used to that.

gg

BMW blinker operation is designed by ex CIA headgamers. Toggle UP for LEFT turn, toggle DOWN for RIGHT turn...WTF???