Vintage BMW Motorcycle Owners

New to forum. Power loss consistent after bike warms up - 12 to 15 miles of riding. Recently cleaned magneto, installed new coil, points, condenser (from Vech, who has been great.) Properly set gaps, timed ignition. Also changed rings on one cylinder with low compression. New plugs, good spark. Starts on one kick cold. Bike will re-start if left to cool some, but exhibits pretty immediate power loss when up to temperature. Bad coil? Condenser? Both? Any way to test either?

I would check the compression cold and hot. I would guess that you have low compression when the engine is hot.

Did compression when bike was warmed up, first dry - showed low compression on one side. Did again wet, which brought up compression, so replaced the rings on that side. If compression is now significantly different between sides, can that result in power loss?

What are your compression numbers? Have you considered a leak down test?

Dry they were 125 and barely 100. Have not re-tested with new rings. And, have never done a leakdown, but maybe should?

Did you ensure that the carb slides were completely pulled up when doing the check? I'm thinking that 125 psi compression is not that horrible...better if both sides are the same. If your compression numbers are something you can't live with, then a leak down test will tell you were the air is escaping to. That way you know if the problem is the rings or if it's the valves.

Did you check both Carbs to make sure they both had enough gas in them after running. I like to hook up a timing light to the plug wires. Point at my face and pull the trigger for both sides, see if there is any difference in the firing of each. No it wont blind you if you hold at arms length.

Did not check carb slide position. Will retest compression, and check firing with timing light. Still thinking about new coil/condenser if all else checks out.

Retested compression while hot with slides open. Numbers topped out at 120, even on the new ring side. Went for another ride after above mentioned compression (2 kicks to start), lost power at top of 2nd, into 3rd. Turned around and went home.

Do you have fuel filters in the fuel lines? If so get rid of them and retest.

Could also be dirty filter in the petcock. Anything slowing fuel flow.