115 HP 1978 Johnson Low Power

[grw5]

I'm trying to get this old Johnson to run right again. Any help would be appreciated. The general symptom is that when I get it into the water and increase the throttle, it will not go over 2500 rpm and the boat won't plane out. I did get it to plane out once for a while, but then it dropped back to a lower rpm. The last time I took it out, again, it would only get 2500 rpm at w.o.t., but then something happened where I could not give it any more throttle past 1500 rpm or it would die.

This is what I have done, so far. I did a compression test and all 4 were between 105 and 110psi. I checked the timing at idle, checked for spark at each cylinder, tore down the carbs, which looked perfectly clean with no sign of varnish, replaced all the spark plugs, and I ran all the tests I could in the SELOC manual with a standard volt/ohm meter. The one thing that did not meet specifications was that the resistance on the charge coils was reading about 305 ohms, on both coils, and the spec was over 500 ohms +/- 75 ohms. Could this be causing my problem? I didn't want to buy this part, which is a fairly expensive assembly, unless I had confidence it would fix it. One reason I hesitate is that both charge coils were reading exactly the same, which I would think is unlikely that both would fail to the same value. I have not checked the spark when under load, but it seems to run smooth, it just doesn't rev up. The charge rectifier also checked out. When running it I would squeeze the priming bulb which would be stiff and have no effect.

I am about ready to take it to a mechanic, but I would like to get some input from some of you with experience so that I can fix it myself. I appreciate any of your suggestions.

grw5

 

[Joe Reeves]

Re: 115 HP 1978 Johnson Low Power

If you didn'y manually clean the high speed jets that are located in the bottom center of the carburetor float chambers (2 to a carb), do so.

The ohm reading of the charge coils that provide power to the powerpacks (Brown, Brown/Yellow) on one bank and (Brown/Black, Brown/White) on the other bank should be 560 ohms +/- 75 ohms.

If you are absolutely sure of the readings you obtained, then the stator is not providing the necessary voltage to the powerpacks.

Remove the flywheel so that you can visually inspect the stator for cracks, any substance oozing out of it anywhere, etc.

With the spark plugs removed, at cranking speed, the spark should jump 7/16" spark with a strong blue lightning like flame.... a real SNAP! Does it?

The flywheel nut when installing must be 105 foot pounds.

 

[grw5]

Re: 115 HP 1978 Johnson Low Power

I have checked all the high speed jets on the carbs. I blew them out and even stuck a cutting torch tip cleaner in the holes to make sure they were fully open (being careful not to file the hole) and they were clean.

I will check the charge coil resistance, agian, with a better quality meter, and I will pull the flywheel off and inspect them as you suggest.

The spark plugs do have a good blue spark, when pulled, and the engine is cranked. I will try to verify the length of the spark without shocking the @##%)$ out of me.

Thanks for your suggestions!

 

[grw5]

Re: 115 HP 1978 Johnson Low Power

I double checked the charge coil resistance with a good, calibrated meter and I measured 295 on one and 297 ohms on the other. I was not able to get the flywheel off to inspect the charge coils because I didn't have the right size socket.

I also checked the spark and would get a good 7/16 to 1/2 inch blue spark. While the engine was idling at about 1000 rpm I pulled the plug wires on each plug indivudually to see if each was still firing. There was ralatively little change in the sound when pulling the wire clear of each plug, except for when I pulled the number 2 plug (below number 1), the engine would die.

Anyone have any more thoughts or suggestions?

Thanks

 

[Joe Reeves]

Re: 115 HP 1978 Johnson Low Power

And the spark with the spark plugs removed at cranking speed as per my previous reply?

 

[wavrider]

Re: 115 HP 1978 Johnson Low Power

I have the same engine as you do.

Check the spark at "cranking speed" 300 RPM, not with the engine running.

I remove all plugs, ground the three plug wires you are not testing so no stray voltage going around. Use a spark tester found at any auto parts store, can be adjusted to 7/16 inch,( joe reeves has a post on how to build a do it yourself 4 plug tester, simple and easy to make). which ever tester you use make sure it is 7/16" space, test each circuit to see if you get a 7/16" spark jump.


When I first got my engine I was chasing the same gremlin, DVA adapter works great to get actual ac measurements when the engine is running.

Use the search function and there are several posts on how to build a DVA adapter.

http://www.boatpartstore.com/page40.asp

The above is a great link for measurements info.

My problem turned out to be fuel pump, it was weak and would not let it get above 2500 RPM, I replaced the pump after rebuilding carbs and replacing all the fuel lines. Been running strong for couple years now.

Make sure you use a fuel stabilizer in the fuel, that way no more varnish in the carbs.

 

[grw5]

Re: 115 HP 1978 Johnson Low Power

Thanks wavrider and joe reeves for your suggestions.

Yes, I did check the spark at cranking speed. I did not have a spark tester and I did not ground the other 3 plugs. With the spark plug removed and plugged into the wire, I held it at various distances from a grounding bolt and eyeballed a distance of at least 7/16 that the spark would cross. I will buy or either make a tester.

Previously when testing it in the water I tried pumping the primer bulb trying to assist the fuel pump, and it had no effect on the problem. I had new fuel lines and filter from the engine back to the tank (also new) and last night I replaced all the fuel lines inside the engine because I would get some fuel leakage when priming. This may have permitted some air to be sucked in.

I will try to rig up the DVA circuit and run the other tests.
Thanks again for your advice!

 

[Joe Reeves]

Re: 115 HP 1978 Johnson Low Power

(Spark Tester - Home Made)
(J. Reeves)

A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.

Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:


..........X1..........X2

.................X..(grd)

..........X3..........X4

 

[grw5]

Re: 115 HP 1978 Johnson Low Power

Here is an update on my investigation.

I couldn't get ahold of a DVA, but based upon some other posts, I learned that an oscilloscope will work just as well. I borrowed one from work and went through all the SELOC tests for the charge coils, (produced 150 v peak), timing sensor, and power packs, while cranking the engine with plugs removed. All the tests checked out. Catching the output pulse from the powerpacks to the coils was a little tricky on the o-scope, requiring several tries.

I tried to pull the flywheel off to check the stator for cracks and ooze, but I didn't have the right bolts for my puller. That will be a job for tonight.

I made a spark tester, similar to J. Reeves, but used some 12 ga. copper wire instead of nails stuck through holes in a piece of plywood. That way I could have a longer wire on the back side, to run to the boots and then bend a little ball on the end for the boot to snap onto. The center ground could also be long and run directly to a bolt. The wires were bent to clear a 7/16" gap and I had a strong, whiteish blue spark on all cylinders. Kindof neat to watch at night! I will send you pic's if interested.

So, now I am confused. Do I have an ignition problem that only occurs at higher power levels, or is it a fuel problem, or something else. Perhaps it's my fuel pump as wavrider said. I think I will order one, in the mean time. I will also take it out this weekend again and see if repairing the fuel lines may have helped.

Any more comments or thoughts are appreciated.

 

[wavrider]

Re: 115 HP 1978 Johnson Low Power

Ignition seems good as per your tests.

Fuel or timing would be what I would lok at next.

top of the forum page is Joe Reeves timing procedures, works great and does not require you to run the engine.

fuel filer replaced, fuel lines replaced, good start still does not tell the condition of fuel pump. If you want to test the fuel pump can use a pressure gauge inline or rebuild it with a kit or replce it with new. I dislke throwing parts at an engine but when it comes to fuel pump kits not to expensive.

A dva adapter is just a full wave bridge with a filter cap, use vtvm on dc setting divide by 2.8 to get peak to peak ac reading.

 

[Joe Reeves]

Re: 115 HP 1978 Johnson Low Power

As Wavrider suggests in not so many words, you may have the timing advance stop screw set wrong whereas the timing would be too far advanced. If so, the normal full spark advance timing, which is always reached before the carburetors open fully (keeping it simple) would be firing against the engine. You can check and set the timing as follows................

(Timing At Cranking Speed 4?)
(J. Reeves)

NOTE: If your engine has the "Fast Start" feature", you must disconnect/eliminate that feature in order to use the following method. The "Fast Start" automatically advances the spark electronically when the engine first starts, dropping it to normal when the engine reaches a certain temperture.

The full spark advance can be adjusted without have the engine running at near full throttle as follows.

To set the timing on that engine, have the s/plugs out, and have the throttle at full, set that timer base under the flywheel tight against the rubber stop on the end of the full spark timer advance stop screw (wire it against that stop if necessary).

Rig a spark tester and have the gap set to 7/16". Hook up the timing light to the #1 plug wire. Crank the engine over and set the spark advance to 4? less than what the engine calls for.

I don't know the full spark advance setting your engine calls for, but to pick a figure, say your engine calls for 28?, set the timing at 24?. The reasoning for the 4? difference is that when the engine is actually running, due to the nature of the solid state ignition componets, the engine gains the extra 4?.

If you set the engine to its true setting at cranking speed, when running it will advance beyond its limit by 4? which will set up pre-ignition causing guaranteed piston damage! You don't want that to take place.

No need to be concerned about the idle timing as that will take care of itself. The main concern is the full advance setting.

Be sure to use your own engines spark advance settings, not the one I picked out of the air here in my notes.

 

[grw5]

Re: 115 HP 1978 Johnson Low Power

I disassembled the fuel pump and I saw nothing that would indicate a problem--diaphram looked and valves looked good. I reassembled until I can get a kit.

I pulled the flywheel off and the stator looks good. There were only a few minor cracks in the plastic right where the big bundle of wires go in.

I tried to check the timing advance stop per Joe Reeves recommendation, but my timing light was too weak against the bright daylight. Will need to check at night.

One thing that really puzzles me and which is probably a clue to my problem is that when I pull the plug wire on No. 2 cylinder while it is idling, the engine dies. It will not die when I pull any of the others. This suggests that one of the other cylinders is not firing to keep it running. Does anyone know the firing order and can suggest which cylinder I should be looking at. Another bit of info. When pulling the plugs, which were new when I started this project, I observed that 3 had some carbon on the insulator, like there was heat and combustion going on, and the 4th looked almost like new. I can't tell you which one this was because I got them all mixed up during to spark test.

I am going to do another compression test and go through the carbs again. Any other suggestions?

 

[wavrider]

Re: 115 HP 1978 Johnson Low Power

That plug may not be firing.

Using a timing light to check for fire is sometimes miss leading, as I found out on a different project I was working on. The timing light will light if there is a pulse/voltage from the coil. It may be weak fire. Spark tester is best way to check that there is fire to the plug. Needs to jump a 7/16" gap with big blue spark.

The spark plug in question may be faulty. Also look at the plug wires, see if there is any corrosion in the boot where the conductor connects to the metal tab.

You can also try changing around the coils to see if this makes any difference in which bank runs when you pull the spark plug wires off.

Clean all the ground wires coming from the amplifiers. Sometimes a dirty or high resistive ground can cause erratic running. Clean the ground stud on the block where the ground from the battery connects to the block.

When you test the timing at night with your timing light take a good look at the engine while it is running to see if any of the spark plug wires are arcing to ground. Usually this can't be seen in the daylight.

Post your results after you try if the engine still does not run correctly.

Also try disconnecting your rectifier. Some say it has nothing to do with the ignition circuit, but I have seen them cause some strange problems when they short out.