Vintage BMW Motorcycle Owners

Hi everyone, very new to the community. I have something of a strange problem that I cannot find an answer to if any ideas please chime in. My R60/7 was running fine last year then suddenly without warning after warming up a few miles it started to backfire, starting slowly when accelerating then even more to a point it was almost impossible to ride. My guess was bad coils. I since then moved back stateside and bought a new set of coils and replaced the plugs. On my second long trip today I started to get the same thing. Slowly backfiring at acceleration and progressed worse to a point of almost complete power loss unless I was at a high rpm. So now I'm completely stumped. Owned the bike for 30 years and never had an issue until now. Does anyone have some ideas what could this be? What should I check?

Welcome to the forum! That does sound pretty strange to just start doing that for no reason. I think the best thing to do is to start with the basics. Do a valve clearance check, then do a tune up, checking points gap clearance and timing. You might find that the rubbing block on the points has worn down enough to completely change the timing.

So, try doing those basics and see how the bike performs.

There are various things to check:
First thing that comes to mind is to check the carb diaphragms, does one have a hole in it?

Then float bowl level, and how old are the plug wires and spark plug caps? They can be checked for proper resistance, but if old I'd just replace them.

Hi, thanks for some of the ideas I appreciate it. I have not been Stateside long enough to rejoin a BMW riding club. I learned so much just riding with the experienced and good BMW owners in my early riding life, so the forum here really helps. I will recheck all the gaps, points, and tolerances. I replaced the spark plug cables last year but I bought another set just in case. I will look my electrics over and check the slide carbs. It was pretty disappointing as I thought I had successfully fixed the problem and now it's back again, ughhh.

Since it runs decent when cold, most things are eliminated. Somethings are affected by heat and metal expansion.
The coils are a good guess; but I'd think it could be your valve clearances are too tight. Then, when heated the valves may not close causing poor running and backfiring. You may have original valve seats that are failing due to Lead free fuels.

Mike

I went through the bike looking at everything in basic tuneup. I replaced and re-gapped the points and condenser. I checked the plugs. I looked at the valve clearances and found the intake side very tight on both cylinders. There was some minor end play but checked that too. I will do static timing next and once that is done, I will do a test run and see where this goes. I'm hoping there was some problems relieved. With the Bing slide carbs I can't think of any potential problems related to the previous symptoms that will cause a need for replacement parts. So far so good.

Tight valves in my opinion tend to result in poor idle performance, so finding the intake valves tight might be a step in the right direction.

People get hung up on the requirement that the gap be exactly 0.016" but that can really vary quite a bit on our two-cylinder bikes. Get the gap set, check timing, and regap if you run out of rotation on the points plate. I think you can go down to 0.012" or up to 0.022" if needed. Small gap changes makes big differences on timing.

I sincerely hope so. There is a big variance in valve clearance as well as the points. I couldn't find my Clymer so I referenced my Haynes. I was reading in my Ignition section that a faulty condenser can cause backfires and are notorious for doing this when hot. This could be one component that was contributing to the greater of the problem. Once I complete my Static timing I'll know more later. In the process of appropriating an analog multi-meter.

The condenser could very well be the problem. My friend had one go bad on his 79 RT. Had the same symptoms. St.