Seafoam.
We had problems getting the boat in the water for awhile, and had one motor start popping and sputtering. The seafoam cleared it up.
They recommend getting it into the carb via the fuel system, and when it starts to smoke, shut the motor off for abit.....15 to 30 minutes. Then start the motor up and run it until it doesn't smoke anymore.
I changed out the fuel filter on the problem motor(spin on in the cockpit), and filled the new filter with seafoam prior to installing it. I added a couple of cans to the tank also.
You can get it at auto parts stores. I buy mine at O'reilly's
Dump the old fuel in the lawn mower, refill the tank with new fuel and add some seafoam to it. Try and figure out away to get the seafoam directly into the fuel system....if a guy had an extra fuel line with a primer bulb, and the fitting that hooks to the motor, you could drop the other end in the can of seafoam and use the primer bulb to suck the seafoam out of the can thru the line and into the carb.
You could start the motor on the seafoam, when it runs and starts smoking shut it down, hook to the regular tank, and when your done waiting, start it and let it run.......don't forget the muffs.
Here's a vid
http://video.google.com/videoplay?docid ... 726229173#
A young man painting my eaves on the house last year recommended it to me.
Gordon