I’ve had to get back to the B31 - this lack of performance is really bugging me, especially after all the money it’s had spent on it (way more than it’s now worth). I’ve taken the head and barrel off again and again, after less than 50 miles, the piston crown has thick carbon deposits on the spark plug side/middle but nothing on the opposite side (see photo). The scratches are where I have been poking a screwdriver through the plug hole before lifting the head and the loose bits on the farside are where I have scraped some carbon off.
To me it looks like incomplete/poor fuel burn in the combustion chamber but I just can’t see any reason for that. As stated previously everything is bog standard with a new 276 carb, a really strong spark from a newly reconditioned mag, new rebore, piston and rings, new valves, springs and guides. Valve and ignition timing has been rechecked and is correct.
Any thoughts anyone?