Simple things first: catch the fluid you drain out of the carbs so you can see whether there is water present.. if that's not the problem, check the air intake... a rag left there, for example, can do a good job of strangling the power.
<edit> My guess the pilot jets are clear, if it starts and runs at low speed the problem sounds more like air or fuel starvation.
One check you can do when it's dark is check the plug caps, leads and coils for sparks tracking.
<edit> My guess the pilot jets are clear, if it starts and runs at low speed the problem sounds more like air or fuel starvation.
One check you can do when it's dark is check the plug caps, leads and coils for sparks tracking.