I concur with the spark plug replacement. Also probably worth adjusting the valves. Pretty simple for the Rappy 700 (No shims)
+1 adjust those valves... simple....
could be something ignition... stator..... coil... but doubt it. it's only runnin rough for 30 seconds...shouldn't be something too terrible
if it runs fine with throttle for those 30 seconds, not sure Id worry too much.
oh..... just thought of something... when it went from one extreme temp to another winter to summer, Id have to play with the idle screw on mine.... it didnt like to idle cold in the winter, so id turn it up...but then in the summer, have to turn it back down.
Im only talking like 1/4 turn here....Don't turn it alot, but that might help you.