Generally full throttle on the governor 3300 is about the norm, or at least where there set from the factory, what its actually running at now will need the use of a photo tachometer

Typically small engines run at approximately 3500RPM as their stock maximum.

Your engine has a set no load speed of 3300RPM.

I couldn't find the RPM on that engine, BTW the model is 28Q777. I did find the manual and parts list but that won't help you - http://www.briggsandstratton.com/us/en/s...

The other 15.5 B&S runs at 3300 max governor speed -http://www.briggsandstratton.com/~/media...

Now that you have the right model #, call a small engine shop the verify it in their cross reference book.

I have a 15.5 hp briggs lawn tractor engine model # 280777 type 0668 A1. I am trying to use it to turn a hydraulic pump so, I need to determine how mant rpm the engine turns. Does anyone know thanks