please help me

[Johnnykat]

Good morning all. I have a 1992 120 HP Johnson v-4. New water pump, new thermostats,new lower unit, new power pack. It is sort of hard to start. Always have to give it a little throttle to get it going. It used to top out at wide open at 5200 rpm but seems to have lost something. Wide open throttle now is about 4800 rpm and yesterday, it sounded the alarm and shut down to about 2500. pumping water good and idles ok. checked compression on it and 1 cylinder is about 5 to 7 lower than the rest. Got caught in a storm and had to idle back to ramp if i tried to speed up it would spit and sputter and not go past about 2500rpm. Lower than that it seemed to run smooth. Parked and shut off the boat, walked to truck and backed in to load. Fired up boat and it ran fine, loaded and revved back up to 4 grand like nothing. please tell me motor is not trashed.

 

[malta]

Re: please help me

Not an expert, but it sounds like you may have a burnt plug. I used to run a 90 hp nissan - 3 cylinder - and once in a while, one of the plugs would burn out. When it happened, it would idle nicely, but as soon as i needed that bit of power, it would spit and sputter (quoting you) and refuse to go beyond 2,500 revs - absolutely no power, which was a headache if i happened to be out in a bit of a lumpy swell. Sometimes, the plug would clean itself and run fine, but who wants to take that risk? I learnt to always have a spare set of plugs and that the culprit was always the lowest of the three plugs that would go, so i'd simply change that one, and it would run fine. This would happen every month or so. never found out what the culprit was (maybe the oil mixture was wrong for that cylinder). Hope this helps.

Cliff

 

[Johnnykat]

Re: please help me

Good morning all. I have a 1992 120 HP Johnson v-4. New water pump, new thermostats,new lower unit, new power pack. It is sort of hard to start. Always have to give it a little throttle to get it going. It used to top out at wide open at 5200 rpm but seems to have lost something. Wide open throttle now is about 4800 rpm and yesterday, it sounded the alarm and shut down to about 2500. pumping water good and idles ok. checked compression on it and 1 cylinder is about 5 to 7 lower than the rest. Got caught in a storm and had to idle back to ramp if i tried to speed up it would spit and sputter and not go past about 2500rpm. Lower than that it seemed to run smooth. Parked and shut off the boat, walked to truck and backed in to load. Fired up boat and it ran fine, loaded and revved back up to 4 grand like nothing. please tell me motor is not trashed.

Another addition to the saga.................cylinder with slightly lower compression.....tiny water droplets on plug.....