Reverse Thrust Kit?
Ray,I had a Johnson 9.9 on a boat many years ago, and suffered from the same problem. I could achieve full throttle in reverse, but because the exhaust is thru the hub of the prop, there was too much cavitation in reverse. I vaguely remember a reverse thrust kit I bought from OMC (now Bombadier?). I can't remember the details, but one part of the install called for drilling out three holes on each side of the lower unit, just below the cavitation plate. I remember thinking I'd ruin something by drilling into the gear casing or something, but by following directions it worked out perfectly. In forward, no difference. In reverse, most of the exhaust came out of the six new holes, leaving the prop biting into clean water, and giving a lot more thrust. Maybe call Bombadier and ask them about it???