This post may help someone.My 1985 20hp started surging up and down as I "tried" to race back to the ramp up river as a storm approached.It would not go very fast and kept surging up and down.I made it and at home checked the spark gap test and compression and all was good.The motor was starting to be alittle hard to start the last two trips out.The carb. had been removed this winter and all seemed good till now.After a closer inspection I saw one of the carb. flange nuts was very loose and a big gap at the gasket and the other nut was slightly loose.I try not to over tighten carb. nuts on any type of motor.Now I know what a motor sounds like sucking in too much air.I did get a acouple backfires also or lean sneezes maybe from this.Back out and it ran fine.
