[Jakub]

Last winter I installed new pistons and had cylinders rebored. Between March and November did ride occasionally, altogether about 2400 miles. For whatever reasons have taken the head out and discovered huge amount of carbon deposit.
The bike was running pretty well, no smoke, easy start, fuel consumption at 5,76 l/100km or 49 MPG. Every so often I check spark plugs, nothing to complain.
Ignition was set at 11 mm which is basically 7/16 or exactly as manual advices.

Obviously there are no valve stem seals like in modern engines so perhaps there might be some small amount of oil getting in, than again there is no blue smoke to report.

My suspicion is modern fuel is not in line with old engine. On my other classics I usually change for bigger ignition advance. Modern fuels are of better quality, higher octane number hence they burn more slowly and need more time to burn.

Since changing the ignition advance is not straightforward job I’ll be glad for advice, observations, conclusions.

[Jakub]

Got magneto back. Thanks to global warming I could take bike for a test ride yesterday. During my young years bikes would be locked up from Halloween till Easter. Not so much those days.
Anyhow, the coughing is gone. I have increased ignition advance. From 11 to 14 mm. It seems to improve acceleration.

As for magneto the workshop magnetize it and cleaned up the distributor ring. What might be important, they have also shorten the pickup carbon brushes springs. They claim brush should only lightly touch the ring and aftermarket pickup spring is too strong.