Re: 07 9.9 4 stroke having trouble idling
To start with the "20 hours" on a 3 year old motor is a bad thing. They don't like to sit unused - particularly a 4 stroke.
How extensively did you clean the carb? removed it, disassembled everything, soaked it out with cleaner, inspected the needle valves etc?
If not, that is step 1.
A couple of other causes which may not immediately come to mind that will cause a rough idle are old/dirty oil (yes I know, 20 hours, but it's been sitting for the other 26,260 hours that it wasn't running).
Oil/filter must be replaced every 100 hours or once a year (whichever comes first).
Secondly, have the valves ever been adjusted (should have been done at the end of the first season of use) - a slightly out of spec exhaust valve can cause a crappy idle.
The maintenance schedule is designed based on the assumption that your motor would be run 100 hours per year - so your motor would be somewhere in the 300 hour range as far as the designers are concerned.
Even if you do not run it 100 hours a year you have to maintain it as if you did.
So check your service schedule in the manual and anything that should have been done by 300 hours of run time should be completed very soon.
Failing to follow the schedule can turn a 4 stroke into scrap in very short order...
