Have a new(er) to me Johnson 90 hp 1986 MY boat engine on a ski boat. Probably has 200 to 250 hours on it total, my parents bought it used in 1987 or 88 and I bought from them spring 2018. I have done some repairs and maintenance (new gauges, trim/tilt sensor, fuel filter, plugs and wires, thermostats, rectifier/regulator, a power pack, seafoam treatment, and "engine tune" treatment spray in the carb throsts, impeller).
Seems to run pretty well now, but not sure if something is an issue or not... if I give it throttle and keep the handle so it should stay at say 1600 rpm, it will jump to 2000 rpm for a few seconds before dropping back down for 15 or 20 seconds. Rinse and repeat.
It does this when warmed up, not just cold. It also does it at idle (but only changes rpm about 100). This is as tested in my driveway with the hose on it, have not had it on the water in over a month so not sure if it does it there since putting in the new thermostats (was running cold) and power pack.
Is this even a problem or is it typical of these engines? If not typical, any thoughts on what it could be(air in fuel lines, carbs problem, etc)?
Seems to run pretty well now, but not sure if something is an issue or not... if I give it throttle and keep the handle so it should stay at say 1600 rpm, it will jump to 2000 rpm for a few seconds before dropping back down for 15 or 20 seconds. Rinse and repeat.
It does this when warmed up, not just cold. It also does it at idle (but only changes rpm about 100). This is as tested in my driveway with the hose on it, have not had it on the water in over a month so not sure if it does it there since putting in the new thermostats (was running cold) and power pack.
Is this even a problem or is it typical of these engines? If not typical, any thoughts on what it could be(air in fuel lines, carbs problem, etc)?