If you remove the cover that holds the generator in place (left side of engine if you look at it from behind) you will find that there is a serie of cogh wheels conecting the electrical starter to the crank case behind the fly wheel there is a "one way" bearing.That bearing locks on to the crank when the electrical starter is running,and will "slip" once the engine is running.Some times when that bearing gets worn(like on my old 86´Tenere) it might lock it self completely and the por starter will be forced to spinn after the engine has started up.

As for starter turning slowly: Have you had jumper cables connected too it when trying to start? in that case what kind of battery did you hook up too it? I have seen starters that have been "fryed" when a big car battery or similar have been used to force them in to action.
OR: Remove the smal cover on the end of the starter (where it connects to the engine,left side) There shuld be a gasket between that cover and the generator cover, if not buy one or make one out of gasket material( 1mm thick) If this gasket is missing the cogh wheels inside it will be pressed too tight and it will be like running the starter with brakes on.

Carbs shuld work just fine,chek the color of the plug when you get it running,shuld be light brown. If it´s black the engine is running fat, and if its white/grey it´s running lean.

good luck hope you will get it running!

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Places to be and things to do, see you all out there!!

Cheers.

Tom.