My guess is the fuel filter is dirty/clogged; it is found inside (bottom) the fuel tank. It can only be confirmed by removing and inspect. As suggested by @ADIOS600, something may be floating in the fuel tank and occasionally clog the fuel filter. Note: Pay more attention to the revs when it happens.
Also, Overheating issue? is the radiator fan working when it gets hot? You should be able to hear/see it.
Also, Overheating issue? is the radiator fan working when it gets hot? You should be able to hear/see it.
