Home › Forum › Ask A Member › Pulsating 15hp detuned down to a 9.9 question › Re: Pulsating 15hp detuned down to a 9.9 question
I’m with Mumbles, many of these engines exhibit the symptoms you are speaking of, especially the older ones. If you dial in the idle mix for smoothness, the engine falls on its face during acceleration, or it may even bog out completely when slowly decelerating through this trouble range.
There were several updates on these engines that included carbs, throttle cams, and cylinder heads. Usually, I have to leave the idle mixture a tad rich to avoid the bogging/lean midrange. You might try retarding the cam pick up as well.
The 9.9/15 differences for the 1975 models were a carburetor, cam, and reed shims. Both engines used the sealed exhaust tube in 1975. I usually found the symptom you describe was worse on the 15hp models, so I would have thought the 9.9hp carb would have improved it. Tell us why your customer wants to detune the engine….