Gilbert put a 4 step reversing unit in the early 346 and later 343 and it didn't work smoothly so the later changed it to the 2 step reverse unit. Both were mounted on the back of the motor. If you have a 4 step unit don't expect it ever to work pretty good. A two step can be repaired but it too is hard to work on. Replacement of the two step is what I commonly do.
If you have an engine with a 2 step compare it with the one on the 346 so you know what you have. If you have a 4 step and are not an expert with repairs maybe a new electronic E unit would be a good option.