Sometimes you try to be smart, yet you do something stupid (and that is aimed back at me).
When all the problems started , I found a fouled spark plug in that "dead" cylinder. Cleaned it a little, spark returned. But still it was fouled inside the electrode and needed replacement. Did I do it? Of course not, got all my nerves jammed with cylinder head take off issues, I simply forgot.
So yesterday we left for a weekend ride with my wife. 400 kms, no issues with overheating (air temperature around 27C, temperature gauge at 10:30 o'clock max). BUT - acceleration didn't feel right. Some horsepower was missing, especially on lower RPMs.
As we have no intercom in our helmets, I had time to think it over: did I put the carbs back in and left an air gap on the boots? But they seated so well and boots are new. Did I break the coils/plug wires somehow? Did I miss the timing? No, no no... triple-checked everything... And then Dang! that damn spark plug!
Went down to the garage today after returning, took it out - almost no spark. Cleaned it a little, spark came back, went out for a ride around home - all power is back!
What a stupid thing to ignore!! And yet I remain calm - at least I found what was wrong. New sparks to come in next week, then inspect if they don't get fouled again.
Conclusion - seems that I fixed my first engine issue, I hope it will last some tens thousands of kilometers. And yes, head gaskets on ST11's can break - even if it is documented as very rare all around forums.
P.S. a rare pic of my ST with all tupperware on
