So I do all my own maintenance and have done for decades. Problem solved everything to date.
This one has me stumped right now.
The motor has a bad habit on first startup of the day of dying under throttle for the first power up.
It will either drop a cylinder and run flat out at a max of around 3500rpm, (just up on the plane) until the 3rd cylinder kicks in and it takes off like a rocket. Or it will stumble and die completely. At which point it starts right up and may stumble again, or may power up. As soon as it powers up on all 3 with no stumble, it is perfect all day. Can sit at anchor 3-4 hrs, fires up and powers up straight away. It will only do this first time each day.
I have stripped the carbs - clean as, re set one float level (slightly out). Checked fuel supply (but makes no sense - runs good all day), checked filters, checked for air bubbles in the line. New plugs, even bought a new coil and swapped that around. One carb seems not to tune quite so well on idle mix. Thats the worst culprit/symptom I can find. Cannot find any obvious issue with it. Have checked the timing. Checked everything I can think of. Replaced the thermostat for a warmer one - the shop suggests they run better at higher temp than factory spec.
I can idle the motor for 5 minutes and it will still die on first throttle boost. Then clears and good to go.
I have run out of possibilities.
Alan