Re: 1974 Evinrude 9.9 won’t idle at low RPMs, need help

[optsyeagle]

I have two of these motors. A 1975 9.9Hp and a 1976 15Hp. I can tell you from experience that the UL81Cs will foul in a couple of hours of trolling and sometimes you won’t even get away from the dock with both cylinders running. As long as you don’t mind surging and bogging, surging and bogging, they work fine.

Go with the NGKs on that model of motor. Just so you know, with NGK the B6HS is a hotter plug then the B7HS. The reverse information was posted previously. Both will work fine for your motor, but the B6HS work better with the 15Hp models. I am guessing the larger carb throat in the 15Hp causes more fuel to carbon up and cause quicker fouling and therefore they prefer the hotter plug. The B7HS in a 15Hp will work but need to be changed every year. All that being said, use the NGK B6HS plug. BR6HS are fine but not needed on your motor.

OK. Really sounds like a carb problem. I would get a carb kit. Pull out that welch plug. Pull out that slow speed jet bearing (looks like a very small plastic funnel hidden well inside the slow speed jet). Soak that sucker in lacquer thinner or carb cleaner and then blow out the passages with compressed air. Do this a couple of times. Then insert a new slow speed bearing into that jet. Insert a new retainer at the outer end of that jet. The retainer will seal the needle. You do not want an air leak or you will get too much air as you have already mentioned as seeming to be the problem. One last point. Once you insert the new slow speed bearing do not use anymore carb cleaner on that area. The bearing is plastic and plastic parts do not like carb cleaner.

Now dial in the needle to lightly seated and back out 1.25 turns. Make sure the carb sync is good. As Fleetwin stated, there is an indented arrow on the throttle cam that pushes on the carbs roller. That arrow should be in the middle of the roller JUST as the carb starts to open. If it is not, it can be adjusted by the hex nuts on the starboard side of the throttle cam. YES, OMC did not make it easy to adjust. You need a thin 5/16" wrench to loosen those nuts without removing the flywheel. I filed one of mine down with a hand file, but it takes the patience of an incarcerated felon to file a wrench like that, but I had the time one day, and felt lucky that at least I was at the lake on a sunny day with a beer in my hand and not in a 6′ x 8" maximum security prison cell filing through a 1 inch hardened steel bar.

Give that a try, would be my best advice.