Re: hello ! ( and about engine temps...)
while I am no expert in anything in life, I think common sense would apply here.
No motor is designed to run at Wide Open throttle for long periods of time.
2 stroke or 4 stroke. so if your question is, can you or should you run a two stroke or 4 stroke at top speed at max RPM for more than 30 minutes then all is well after a 5 minute break. I would have to say no.
I would further go out on a limb by saying a 2 stoke motor if ran in the ideal rpm range for that motor could run much longer than 30 minutes at a time as long if the air fuel-oil mixture was at the correct mixture- ratio.
many things come into play for example how much of the air flow to your air cooled motor gets obstructed by the front forks tire and frame.
also the cool down period needs to be based on other factors than just time as the motor should be cool to the touch if your letting the bike rest.
lets say for argument sake your running your bike on a banked race course at an angle that is equal to or more than your bike resting on a kick stand this could leave your engine starving for oil as the oil has the potential to puddle where is does no good.
I guess where I am going with this is, to answer your question we would need know more about your riding habits and bike setup to know what would be best suited for your specific application.
if your like most people that bolt on a Gas powered engine kit and desire your bike to perform like a motorcycle but run with the RPM maxed out no engine 2 stroke or 4 stoke will be good enough or last long enough to make you happy.
many kit manufactures will claim their motor will do xx miles per hour and get XXX MPG
But many wont tell you that your not supposed to drive it at that speed all day.
or even for 30 minutes at a time.
Honda Motors has a great 4 stroke at a reasonable cost but they clearly state that the warranty is void if used in a Bicycle. Because they know it will be subject to operational parameters that the motor just wasn't designed for.
again I am no expert this is just my opinion based on many years of experience with 2 stoke and 4 stoke motors.
to further add to this a 2 stoke motor will require more work and maintenance
than a 4 stroke motor.
I have used many small engines in equipment from Generator-welders pressure cleaners bicycles mopeds ETC both two stroke and four stoke and in none of the equipment that I have used some all day long some days and days for weeks on end with the only break was to change the oil and top off the fuel none of them even came close to Wide open throttle operation like these bikes experience often.
Heck my first Moped was built by Tomas I think, it was great but I burnt the rings up in less than 4 months as I would hop on it and go wide open throttle at 40 MPH
or better as the roads I traveled were long and straight that seemed to go on forever. this was a case where I should have had a car or motorcycle for those trips as I expected way too much from that poor little moped.