Considering that your engine came from Ralph, I would suggest that you contact him directly for advice regarding your query, as to the best of my knowledge all engines from him are run and tuned before being sent out.

The rpm you quoted on an 18x6W is about normal if the engine is being run with the stock muffler which is quite restrictive. Fitting a less restrictive muffler should show an rpm gain of about 800.

Ralph's number is 928 635 2455.

Karol