Re: trouble with 9.8 MODEL 110
I have a '78 Merc 110. My advice, rebuild the carburetor. Just take it apart and clean it out, there is probably all kinds of gunk in there that has built up over the years. I would be careful when disassembling the carb and try to same the gaskets so that you can reuse them if they're not in too bad of condition. Put the carb back together and see if that fixes the problem.
I had the same problem with my 110, a small piece of trash had clogged up the jet and it would only run with the choke pulled.
Good luck