Modern Vespa

Am I barking up the wrong crack pipe, but is it possible (or even desirable) to add reed valves to a rotary valve engine? Thought I read somewhere that some people had done this. Bad juju or what?

People do that all the time. Either because they want more power, or because there rotary pad is shot. Or both.

But you better swap the crank for a full circle one. Otherwise I don't think there is much point.

+1 on that and don't forget to port the inlet

I don't think reeds yield more HP. My understanding is it is more of a snappy throttle response and improved fuel efficiency, because of the more effective opening and sealing of the intake. Am I wrong on this?

adding reeds dont give more power, the only real reason to switch is if yr rotary pad is shot or if on a tuned engine and you want better throttle response and some other shit too.

adding a reed to a working rotary valve will not improve performance and will most likely reduce it.

If the rotary valve is damaged then adding a reed can help but you don't get the full benefit of a reed unless the flow to and from the reed is unobstructed by the rotary valve or anything else.

Thanks for the answers. This is getting more interesting-er and interesting-er.

Don't know the condition of my motor other than it runs at present. Will tear the entire scooter apart in a week or so...and I do mean ENTIRE. Fix it right or don't bother at all.