115 Johnson misses at idle but not WOT???

[DMAN1968]

Hello all,

First off let me give the available information:

1974 115 Johnson...Compression is 100-105 on all 4 cylinders, tank, gas etc... all new, all good. Even replaced engines fuel hoses and used real stainless steel hose clamps instead of the zip ties that came on it. New fuel pump, 4 new coils, wires and plugs. New rectifier and power pack as per previous owner (well, only about 1 year old, they sure look new). Replaced the sheared keyway, cranked down on the flywheel bolt with a torque wrench to above 125 ft/lbs...more like 150 ft/lbs as I didn't want that to happen again. Rebuilt the carbs twice as I had one of those little freeze plug looking plugs come out after my first attempt. The second time I rebuilt them with OMC kits including floats...let them soak in Seafoam prior to cleaning and cleaned them to within an inch of being able to eat off them...every hole, orifice, crack and crevise. Linked and synched to the best of my abilities using the manual that I have.

Now the problem...It idles well until it warms up...then it drops a cylinder, maybe 2. In gear or not you can hear the miss...no cough...no sneeze just misses enough to kill at low speed idle. Just in time to screw up docking or loading it on the trailer. When I hit the gas she goes fine, the missing goes away and WOT is perfect. With the cowling off I can hear a intermittent tick so my problem is probably arching somewhere, probably in the boots or the spark plug to the block. I haven't been able to run it at night to look for it yet.

My question is why would it only miss at idle? Why would it arch out when under a light load and is this likely a bad new coil, wire or a plug?

Any suggestions would be greatly appreciated and thanks in advance.

 

[CharlieB]

Re: 115 Johnson misses at idle but not WOT???

You said that it idles well until it warms up.

Leads me to think that the idle mixture is a bit rich, by the time it warms up that's too rich and starts to foul plugs until you throttle it and it clears out.

Once warmed and starts the missing, shut it off and look at the plugs carefully, which ones are blackened?

Sorry but you are going back into that carb again, is it an adjustable idle or is the air bleed restricted?

 

[crb478]

Re: 115 Johnson misses at idle but not WOT???

Have you tried to clean all of your connections and grounds to all of your electronics? For what ever reason they seem to be very finicky. It may be making a better ground when you speed up the engine but not at idle. Just throwing out ideas.

 

[DMAN1968]

Re: 115 Johnson misses at idle but not WOT???

I'm not sure what "air bleed restricted" means...The carbs only have low and high speed jets with no adjustments possible as far as I can tell.

 

[ezeke]

Re: 115 Johnson misses at idle but not WOT???

May not be the problem, but worth checking:

In 1973 and part of 1974 many V4 engines, choke solenoids had two wires running positive current, one from the choke switch at the helm, and the other from a temerature switch located next to the lifting eye. As late as 1976, the wiring diagrams in the service manuals still showed the temperature switch even though it was not installed on the engines.

Subject to a 1974 Service Bulletin from OMC, most of the choke temperature switch controls were disabled or removed from the engines by service departments because they caused the engine to run as yours does. If yours is still wired, you may want to disable it. If you find that it is, please report back and I will try to get a copy of the bulletin to you so that you can correct it and rewire the terminal block.

 

[DMAN1968]

Re: 115 Johnson misses at idle but not WOT???

Thanks folks for the ideas. I did clean the connection on the battery, starter, coils etc with my dremmel and a small wire wheel attachment. I will go back and check them out again.

Would an intermittently fouled plug cause this? I still wonder about the arching?

I'll also check to see if the choke is wired as ezeke says...I seem to recall that it has a double wire running to the solenoid and then a very short one to the block right under it.

The boat is at the camp right now about 45 minutes away...wish it was as easy as stepping into the garage to check it out.

 

[newtong_ware]

Re: 115 Johnson misses at idle but not WOT???

I have a '76 115 Johnson. I just a few months back finished a top to bottom rebuild after a massive piston ring failure.

I would suggest cranking the motor with the cowling off either early in the am or late in the pm when the light is poor and watching around the spark plugs real close. I had to replace a boot on a brand new coil, because for some reason the plug started arcing from beneath the boot down to the area of the plug that the wrench fits onto. You could hear it when it start to happen, the rpms would drop, if I was running down the river, it would sound like it was working way too hard. I was just tinkering and looking one day just before dark with it idling with the muff on, when I looked and saw that little spark.

These are really strong motors, but they have some quirks. As for the link and synch, the best info I found on timing was from Joe Reeves with his method of setting the timing without running the motor at wot. That post is easy to find in this forum, just alpha search "timing".

As for the temperature control switch, I need the info to take that puppy offline myself.

Good luck!

>>>>Newt

 

[Theoutdoorsman]

Re: 115 Johnson misses at idle but not WOT???

This may sound a bit too easy for a fix, but at what rpm's does the outboard idle? I'd venture to say, if it were arcing at an idle, it would most likely be even more noticable as you attempted to increased speed. The reason I'm curious about the idle speed is that you appear to only have the problem when loading and unloading the boat from the trailer. Every other aspect is fine. It should idle between 600-650 rpm's. I like my idle set to 650 rpm's. If all is well with the idle speed, I'd look at the port side on the cowling. I recall another member having a problem with his plug boot arching to that particular latch and causing some issues. Just some thoughts to throw at ya. Good luck with the fix............ ALAN

 

[DMAN1968]

Re: 115 Johnson misses at idle but not WOT???

My tach is less than accurate unfortunately, I set the idle at the lowest setting it would go to and still idle well...which it will do until it warms up. It doesn't just happen loading and off loading at the ramp that's just when it's the biggest pain. Going through the no wake zones at slow/idle speeds the miss is very noticeable...I have to bump the throttle up a hair just to keep it from killing.

I considered the cowling arching issue but I could hear the faint tick of an arch with the cowling completely removed...just next to impossible to look into the plug recesses while it's on the water. It stumps me as to why the isn't an issue while running above idle.

Thanks for all the ideas so far...some things to look into. Anymore ideas anyone? I'm open to all thoughts.

 

[Theoutdoorsman]

Re: 115 Johnson misses at idle but not WOT???

If the tach isn't accurate, I'd deffinitly find one that was.......first! Secondly, I'd make any necessary adjustments to the timing and idle, via checking it with a timing light and the good tach, to rule out a bad link and sync. If it isn't already within spec, I'd make it that way. Then, if the problem still persists, I'd run the outboard on the muffs, in the dark with the cowling removed, and investigate your hunch about the electrical arching. If it is arching, you'll likely see it plain as day. Something tells me that it isn't, but that's just me. I truely believe you have a timing or idle, or both, issue. Could be something as simple as a sticky timer base.

 

[ezeke]

Re: 115 Johnson misses at idle but not WOT???

The thermal switch that controls the the automatic choke's solenoid keeps the choke responding whenever the water temperature at the top of the water column is less than 100 degrees F.

When the engine is at idle or when running slowly, or if the thermostats are not fuctioning properly, etc., the switch will continue to close the chokes, flooding the engine. As you increase speed, the engine will warm up enough to open the switch.

The source of the information is February 1974 OMC Service Bulletin # 1335.

 

[wavrider]

Re: 115 Johnson misses at idle but not WOT???

If it does not turn out to be the choke wiring and still hear the tick fo an arc.

I read on another post that the poster sought his stray voltage arc by using a spray bottlle, lightly misting his heads and block where the sparkplug wires were run.

Started the engine at night and looked for the blue sparks. I have never tried the wetting method but have chased arc's after dark to see where they were coming from.

 

[ezeke]

Re: 115 Johnson misses at idle but not WOT???

There are several possibilities on the clicking sound that the arcing makes:

One is that the rack that holds the ignition coils is not grounded well. There should be a minimum of one grounding strap to the starboard cylinder head from the rack and adding one to the port cylinder head is better.

Also, the ignition coils on a motor of this age need to be removed so that the base of the coils can be cleaned to assure good contact with the rack. The ground wires from the coils are attached with the same screws as those that hold the coil to the rack.

The spark plug wires must be solid core.

When a plug is arcing, a .04 gap is ill advised; use .03.

A spark plug's ceramic insulator can be cracked without it being visible. If it is, the spark will jump the crack.

If the tan wire from the temperature switch is too close to the park plug wire it can arc to it.

One other thing you may or may not know; the hand grip at the back of the engine cover is set up perfectly to allow the rain to run all over your ignition system whenever you store the motor tilted up. It is especially well aligned to run water on top of your powerpack.

 

[DMAN1968]

Re: 115 Johnson misses at idle but not WOT???

Quick Update...

A friend of mine went to the camp today and used the boat to run some supplies to his water based camp. He said it ran great...til it warmed up and then had the idle problems.

Anyway, I asked him to run it on the muffs in the yard after it got dark. He says there is definitely an arc at the boot near the plug on the top cylinder, starboard side.

Now I have something to focus on...still odd that it doesn't do it at WOT. I think I'm going to try the NGK boot idea that has been suggested (if I can find them around here). I also will give the plug a good checking out...even though it's new doesn't mean it's not broken.

 

[DMAN1968]

Update...

Update...

Just a quick note to let folks know what the outcome was. I finally went ahead and bought some new boots for the plugs (not the NGK...couldn't find those). They were made by quicksilver and were at the local marine dealer for all of $2.69 each...went ahead and changed them all. That solved my arching issue completely and most of my idle issue as well. Some fine tuning with the idle screw and a short test ride seems to find that my engine is running well again.

Thanks to all who helped me solve my problems and hope this information can be useful to someone else.

 

[tschamp20]

Re: 115 Johnson misses at idle but not WOT???

i had the same problem. be sure to use die-electric grease in the boots. good job.