A good description of the symptoms is always helpful. Liek the doctor ask, "Can you tell me what's wrong?" Me, " I thought you went to med school
for 12 years!"
BTW - My 2 stroke
experience is primarily with dirt bikes but should be pretty similar.
1/ First start of the day - No problem, starts right up, idles fine and makes full revs in neutral, forward and reverse. It blows no smoke, burns no oil
and makes appropriate sounds.
2/ After 2 minutes it still runs smoothly in forward, reverse and neutral with no smoke, stuttering or any other condition except it is power limited to approximately 1/2 to 3/4 of full power. It revs fully in neutral (no load)
3/ It will run as in condition 2 indefinitely although I have run it for 45 minutes to 1 hour in this condition
4/ If I park it for 2 hours it will restart cleanly with no trouble as in condition 1 and the cycle will continue as through condition 3.
5/ The engine
is 10 years old has been trouble free until now and has never had any major overhaul
6/ The ignition system, fuel
system has not been worked on other than routine spark plug
and wire changes and fuel filter
needs Fuel/Air in the right ratio, a spark at the right time in the right place and compression
- I view this as a low possibility. Low compression indicates bad cyclinder sealing and I would expect smoke and oil consumption
to be reported. If yuo have the tools a compression leak donw check is very cheap
Fuel/Air of the right ratio - The carb is probably dead simple and the mixture should not change, however the time element does not make sense. Why would the fuel
air mixture change over time or temperature.
Dirty fuel system - Very cheap
to clean and inspect and flush the fuel system. There have been cases I know of where debris dislodges at rest and floats out of the way or sinks to the bottom but underway or after time the debris migrates to partially block the fuel system. A fuel filter
and a cleaning
of the fuel system is very cheap. It could be debris in the carb fuel bowl. Dirt in the carb may be harder to sus out requiring carb removal
and disassembly but it is still virtually free.
I assume the carb has a float system. We have had partially sunk carb floats before. They allow the engine to actually flood as the fuel eventually fills the bowl and flows out the carb vent into the intake. This however seems to manifest usually as an engine that bogs down when throttle is applied off idle.
Reed Valves - I like this one very much. Again this is an inspection
Air filter and filter box clean? - Nuff said.
Spark at the right time -
Electrics can have all kinds of different failures and often exacerbated by heating
- Ceramics fail and sometimes can show up when hot "bleeding" a spark to ground or the spark breaks down and is not full strength.
Coils - I have had al kinds of weird failures with coils from low power
to complete failure when hot and working fine again when cold. Coils can be checked for resistance when hot and cold but you will need a manual to get the specs.
Plug wire - Insulators and conductors can both have failures.
I guess that's about my brain dump. I don't post it to suggest anything. Simply hoping that something might spark a thought.