Forum bmwbike.com

I am having problems starting a R69/2 after driving 1/2 to 1 hour. There are no problems with the ignition system and when started the motor run very fine. When the motor has cooled down the motor can be started. Could it be the carburettors?

Any suggestions?

Hard starting when hot is typical of a bad coil. I think the varnish insulation on the fine wires of the old coils deteriorated over time, especially if the bike was stored where condensation could form on it. The heat of a hot motor causes a portion of the hundreds of windings to touch each other, so these wires short out, and the coil loses power. It does not make enough spark when hot run the motor, but not start it. Let things cool down, and it will start.

If you think this could be the case with your bike, try replacing the coil. Do not get a black or red repro coil as they are known to fail soon. Get a grey repro coil from either Bench Mark Works in theUS or Huggett - I think they are the same coil. If you have more time and money, send your old orginal coil to Huggett for exchange against a remanufactured original coil. Possibly Bench Mark Works has these in stock, too.

Hallo,
Allan can be right, but it could also be the kondensator. It is cheaper to change the kondensator and trying if she runs now, when not: try the coil.
rolf

I also get hard starting sometimes, and apart from the state of the ignition coil, it seems in my case to be loss of compression on a hot engine-almost as if the oil film in the cylinders has broken down and allowing compression to leak. On a normal running engine I do not think this will happen, but mine runs hot for some reason, and this is what could cause the problem. However, as others suggest, your first check is condensor or coil.

>

Compression is not factor in starting a gasoline engine. Higher compression does not make the 9.5:1 R69S start better than the 6.8:1 R50.

No matter how low your compression was, successful explosions in the cylinders would make it start. A hot engine is easier to kick, and as you keep kicking it with a bad coil or condenser or whatever, it is easy to think that the ease of kicking is the problem. But the actual problem is weak or no spark. Just my opinion.

Had a similar problem when I put my R-50 back on the road after 20 years. Started fine and ran well when cold but would stall at a stop light and not restart when hot. My first replacement coil was also an old coil and the problem persisted. A new coil cured the problem. Now the bike starts on the second kick hot or cold.
Good Luck.
Drew

Gentlemen
Thank you very much for your answers. I will try your suggestions.
Peter

Allan
Interesting what you say about compression.I had thought that the hard starting problems of my R69S were due to loss of compression when hot, but will now look very closely at magneto problems. It is very difficult to be rational about motor-bike starting problems, because there is a comparison with British bikes, and a lot of BMW problems are never matched by the immaculate starting of a good British single. My comment about compression was due to my bike having strong compression when cold, but when returned to after a hot run to be re-started, appears to have virtually no resistance to the kick-starter. As my engine runs very hot(why?) I put this compression problem down to a loss of oil film, but this is not neccessarily a scientific analysis!

hallo,
I think you can save time not to look at your coil, your problem is something with the valves.
1. Not enough valveclearance when hot(if this happens, your engine gets really hotter than normal), check the clearance when your engine is hot(by turning the pushrods(?)).
2. Not enough clearance in the valveguides, so the valves stopped when the guides changed their diameter while getting hot.
3.(rare) your valveseats does not fits (?)strong enough in the head. when it is getting hot, they loosen their fits(?), tumble down a little bit and keep your valve(or valves) open.
Number 3 you can proof : no compression(and starting) when hot, take the bike and run(2.gear). if it had now compression(and starting) :No.3(eventually 2)
rolf

You are right, it was always the same, not only BMW's. The Shellac used as insulation of the layers of wire brakes down by age. Rewinding and replacing the condenser - saves you troubles. And the hot running of the engine is perhaps due to a lean mixture - a BMW should never run hot NEVER !! Grettings to all of you Thomas