Johnson 120 V4

[knuuttila]

Can anyone tell me what the trim tab on the back of my Johnson 120HP outboard is for.<br /><br />My boat leans a bit to one side under power. Does the trim tab have any effect?<br /><br />Also, I,ve noticed recently my engine sort of jumps momentarily under power, like is has hit something under the water or has lost drive for a split second. Then it carries on ok and does it again a few minutes later. <br /><br />Any ideas anyone?<br /><br />Rgs<br /><br />Brian

 

[Spidybot]

Re: Johnson 120 V4

The trim tab on the antiventilation plate is there to compensate for the torque produced the the prop turning in the water.<br /><br />This torgue forces the engine to one side and to make steering neutral, you adjust the trim tab.<br /><br />As the prop turns it will put a counter force on the boat which may make it lean to the opposite side - most noticeable when at high speed (the hull planing, less hull width in water).<br /><br />Trim tabs (on the transom) would help a lot. Do a search here and you'll see plenty of oppinions on it.<br /><br />The cutouts sounds like ingnition problems. A systematic troubleshoting will tell - a manual will walk you through it.

 

[JRJ]

Re: Johnson 120 V4

UU is correct on the trim tab. As for your "engine jump", another possability I read here some time ago, is your shift linkage is worn out of adjustment. My 1990 Johnson 120 did what your's is doing. (i sold it) Good luck

 

[Spidybot]

Re: Johnson 120 V4

Yez, right. If your gears pop out and in while running it is under tremendous stress and you need to fix it before further running.

 

[bob58]

Re: Johnson 120 V4

Could also be Prop Cavitation

 

[Spidybot]

Re: Johnson 120 V4

Agreed - but if the cutout is hard, it's not a prop cavitation/ventilation thing. That would feel more like a softer dis- and engage action.<br /><br />If it is hard (snappy) with some sort of sound (ratchet) it's gears.. if not sound, only motor dieing shortly, it's more like ignition. If it dies not like a snap, I'd suggest a fuel supply fault.<br /><br />Ignition is obvious and easy to check for - any lose or bad connection could cause it.

 

[LubeDude]

Re: Johnson 120 V4

Maybe a spun hub on the prop? Just guessing!!<br /><br />LubeDude

 

[OBJ]

Re: Johnson 120 V4

I would have to agree with UU on this one. Just the way knuuttila described the symptom tells it all. Knuuttila, you should get the linkage checked and find out if that is the problem. You do not want to operate the rig with this problem. If the linkage is out of adjustment, have it corrected. You will be saving the money on a large bill for new gears.

 

[knuuttila]

Re: Johnson 120 V4

Thanks for your replies.<br /><br />Looks like a call to my trusty mechanic.<br /><br />Rgs