Re: weak ignition system
The 9.9-15 came out in 1974 and right away had a recall for low speed problems. Upgraded motors got a redesigned cylinder head on the 15 and new carbs for both hp motors. There were several spark plug changes. About a year later they redesigned the driver coil and sent out a bulletin about that. When they went to CD ignition, plug fouling was almost non-existent.<br /><br />Now your motors are up to 28 years old, parts are worn,linkage is loose, and age, use, and corrosion takes its toll. Grab the magneto plate under the flywheel, does it "rattle" or move around on its pivot? Chances are it does. There is a repair kit available but its pretty expensive for an older motor.<br /><br />Decarbon the motor, set the points slightly closer to allow for the "slop" in the magneto plate. Change out the driver coil under the flywheel and make sure there are no cracks or arcs in the external coils. Use the UL81 plug, check the thermostat, rebuilt the carb, and synchronize the linkage according to the manual. Your motor will then run the best it can. On the 15's, the engine must prop out close to 5500-6000 for it to troll well. The 9.9 is not as fussy. There is more than just a carb difference between the motors.