Hi
The engine in question is a SPE 26cc and has been tested quite a lot. After first startup the engine was running for abt. 90 min on various load. Next start the problem arised. Engine can run on speeds up to approx. 2500 RPM, but stopps immediately [no "fade" ]before reaching 3000RPM. Following has been done without solving anything:

1. Tested with different gasoline brands, Aspen and unleaded 95 octane between 2-4% synth oil. Gasoline used has been bought the same day.
2. Different needle settings, from 1/2 turn to 4 turn open. Result: engine will not run at all with less than 3,5 turns on H/L needles.
3. Cleaned carb. three times, blown all drillings with air, confirmed open. All membranes in carb. in good cond. Did not make any difference. This was done by two engineers. The pipe J.R. referred to is not leaking. There is no air leakage between carb and engine block.
4. When choke is on, the engine will flood and does not start or stopps immediately when choke is activated.
5. Adjusted plug gap to approx. 1,2 mm and the engine will not start at all. Back to 0,8mm and it starts again with the same problems. Tested with 4,8v and 6v supply with no difference. I have opened CDI box and there is nothing abnormal on circut board, e.g. sign of moisture, corrosion, sign of overheating...

If anyone has any constructive input, I'll appreciate yours...