You can use a dizzy with the vac advance dashpot...just dont hook it up to anything or remove it as it serves no real purpose in a jet boat. You figure a jet boat engine is at full advance by 3,000 RPMs and most jets don't ever run below 3,000 anyway.

Yeah i dont want to buy something i have to fix..

I will find something

2sav

Here is where it would help. Cruising the channel. Pulling the kids on a raft. Idling at the dock.

This would give it more of an advance at part throttle light load and give it better mileage and throttle response there. 

If you are the never see below 4000 RPM and always full tilt, it won't buy you anything.