Johnson 120 missing at mid-high rpm

[mmffpm34]

1989 Johnson 120 VRO V-4 missing at mid to high rpms. It will get on plane fine, starts great, idles good but at high RPM or WOT will miss badly. Here comes the weird part. If you hit the power trim it will run properly as long as the button is held. I have tried a new battery, spark plugs, new fuel lines and primer bulb, looked for a crossed wire or short unable to find one. Any ideas. Sorry I do not have the manual yet boat is new to me.

 

[Joe Reeves]

Re: Johnson 120 missing at mid-high rpm

Check for a loose powerpack to powerhead ground wire.<br /><br />Remove the black/yellow wire from the back of the ignition switch. If this cures your problem, replace the switch. Note... with that wire disconnected, the engine can not be shut down via the ignition switch.

 

[mmffpm34]

Re: Johnson 120 missing at mid-high rpm

 

[mmffpm34]

Re: Johnson 120 missing at mid-high rpm

Joe,<br />I got a 1/4 turn out of the screw behind that switch will run tomorrow and check thanks.

 

[mmffpm34]

Re: Johnson 120 missing at mid-high rpm

Well it wasn't the screw. I bought a new ignition switch haven't put it in yet. I double checked the plugs, 1 looks fouled. The other thing is they are the wrong plugs(never trust the person that owned the boat before you to put the right plugs in). So I installed the proper ones at the proper gap. Now I need to take it out for a spin. <br /><br />Should I change the ignition switch anyway?

 

[Joe Reeves]

Re: Johnson 120 missing at mid-high rpm

Apparently I did not explain myself properly or my reply was misread. The ground wire of the powerpack I mentioned would actually be at the powerpack on the engine, not at the ignition switch.<br /><br />The black/yellow wire I spoke of on the ignition switch is another matter. I did not mean to check that for being loose.... I meant for you to remove it temporarily to see if that corrected the problem.

 

[mmffpm34]

Re: Johnson 120 missing at mid-high rpm

Didn't find any other loose wires. Cleaned up 1 connection where 2 wires joined. (lt blue and lt green?). Need to take it out with the black/yellow wire pulled or should I just replace the switch since I have a new one?

 

[mmffpm34]

Re: Johnson 120 missing at mid-high rpm

anyone else have an idea?

 

[mmffpm34]

Re: Johnson 120 missing at mid-high rpm

Anyone? Anyone?

 

[ob]

Re: Johnson 120 missing at mid-high rpm

I assume that you meant that the powerpack ground is not loose but clean and tight by your post on the 17th.Does your boat have the OMC throttle controller with the rubber cap type lanyard kill switch? If so the rubber could be stretched causing the switch to momentarily ground the ignition.I have no idea why pushing in on the trim button would allow the engine to pickup,but the trim motor wiring is the next place I would check for loose grounds or shorts.Probably not much help ,but I gave it a shot

 

[Bradster941]

Re: Johnson 120 missing at mid-high rpm

Perhaps if you would read, (carefully), what Mr. Reeves suggested and then did it, we could move forward. Otherwise, it's just sort of like waisting bandwith.

 

[Bradster941]

Re: Johnson 120 missing at mid-high rpm

Perhaps if you would read, (carefully), what Mr. Reeves suggested and then did it, we could move forward. Otherwise, it's just sort of like waisting bandwith.

 

[mmffpm34]

Re: Johnson 120 missing at mid-high rpm

Thanks OB, I'm afraid this motor is gonna have to see a real tech. I can't find anything that looks loose or shorted. Still looking for time to run it again like Joe wanted me too I just don't think its an ignition switch problem. One of the dealer techs said it may be the "brain box".<br /><br />Bradster thanks for your valuable input.

 

[Walker]

Re: Johnson 120 missing at mid-high rpm

Your trim switch should be plugged into the wiring harness somewhere. Find that plug and unplug it. If you still have the same problem that will rule out a shorting trim switch or trim wire north of the plug.

 

[mmffpm34]

Re: Johnson 120 missing at mid-high rpm

Thanks Walker I will try that too. I replaced the ignition switch, fuel filter, fuel lines primer bulb, spark plugs, looked for shorts and such. Gonna take it out tomorrow (doesn't seem to miss on the muffs at idle and just above) hopefully I've found the problem but if not I'll try the trim switch/wiring.

 

[mmffpm34]

Re: Johnson 120 missing at mid-high rpm

Well after all of the work it is still missing like a champ. I replaced the ignition switch, checked for shorts and loose wires, replaced spark plugs, fuel lines, fuel filter, primer bulb, unplugged the trim wires still misses. So she's in the shop, I give!

 

[ob]

Re: Johnson 120 missing at mid-high rpm

Did you check out or attempt to bypass the lanyard kill switch on the throttle controls?

 

[mmffpm34]

Re: Johnson 120 missing at mid-high rpm

No, I hadn't really "checked" that but it seemed to be operating normally. Any way I took it in to the shop should hear something today.

 

[mmffpm34]

Re: Johnson 120 missing at mid-high rpm

Some things aren't as they seem. It needs a complete overhaul. Cylinders are scored esp. #3. So Dealer I bought boat from about a month ago is going to rebuild for no more than $1100. Bored, new pistons, gasket set, carbs, fuel pump and water pump. VRO is going. Switching back to good ole dependable mixing. So if it messes up again it's on me not a mystery pump.

 

[mmffpm34]

Re: Johnson 120 missing at mid-high rpm

Oh yeah, its also getting a new overheat alarm. The one it had was not operating.