[Werner]

Tach Andreas,

the high consumption is not unusual. >3.3 l displacement, compressed only 4: 1, this results in a large throughput with very little efficiency (about <15%!).

Leaning only helps if the stoichiometric ratio (fuel / air = 1: 14.5) is grossly incorrect (too rich). But that shows you the spark plug face picture (gray insulator tip). However, the engine temperature must also be correct for this statement. Without a thermostat, I've rarely reached more than 60 ° C, so much too cold.

Special test glas plugs are a very good auxiliary tool. You can see whether the mixture is correct (blue flame) or too rich (yellow), etc.