What is the ambient temperature? This has a significant effect on starting time when below 50F (10C).
Have you confirmed it isn't an electrical
issue (e.g. low starting rpm)?
To confirm the electrical
aspects, try starting using the decompression levers. If this improves the staring time, you have an electrical problem.
1. decompress all cylinders
2. spin the engine
over using starter motor
for 5+ seconds while decompressed
3. with starter motor
still engaged, re-compress one cylinder.
4. if it fires quickly, compress the other two cylinders sequentially.
If the start time after re-compressing is significantly reduced, you have an electrical problem which is causing low starting rpm
If the start time remains unchanged, you have a fuel
or air problem.