I have a 35 HP Vanguard Go Devil surface drive. It is 4 years old and new to me. I have a few questions and need some help.

The motor is mounted on a 1648 go devil boat. I can only get around 20 MPH out of it right now.
The motor was in meed of some maintenance and I have completed most of it. The only 2 things left to do right now are installing a new kill switch and a new tiny tach. Neither are working.

So I do not know how many rpms I am turning. What should it turn (max) in water and out?

I did just yesterday change out the air filter which looked horrible. Could this cause a loss of rpms and speed? I have not had a chance to run it yet.

My other concern would be the prop. It has a 3 blade on it and it looks a little worn to me. It is smooth and rounded, much different from my boat props. Should the blades be edged and defined?

What is the best prop for this motor?

I would appreciate any input on the above.

Thanks

H