Sorry, we have been away racing a lot this past month.
You want to set the pinion tight but not so tight that it grinds. Sounds like to me you have set the pinions (engine) at an angle, be sure when you mesh the gears that the engine is sitting straight and not at an angle. This will cause you to have one pinion correct and the other loose of tight.
When setting the mesh I always check both pinions for correct mesh.