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1974 Johnson 115 Misses on cylinder 3 above 4000 when warm

S

sacriver runner

New member
This is a 1974 johnson 115 115esl74b. When I got this motor it was bogging above 4000 rpm. The following is what I have done.
Resealed the crankcase, replaced top and bottom crankcase seals the top one was bad, new gaskets forward from there and rebuilt carb. This engine has less than 500 hrs. Compression on all 4 cylinders is 120-125. Replaced plugs, wrong ones installed before I got it.
New parts.
Timer base, Power pack, rectifier (replaced with regulated) new coils and UL77V champion plugs. Replaced Key switch.
This motor runs great but now when it warms up, 5 Min at 4900 rpm it misses on cylinder #3. I know this because I checked with a timing light while on the river. It starts losing spark above 4000 and get worse the longer I run it. Idles fine, let it cool off and it runs better again. It stays with #3 even when I replaced the timer base and power pack the second time... Seemed to run better for a bit.
I'm puzzled what it could be.
I can mention all new electrical parts are CDI.
Before I changed the timer base this last time, #3 would shock me through the plug boot while the other plugs did not. I found this out on accident obviously... lol I read about plug wire leaking, could this be the problem?
I did replace the stator but no change so put the one that came with it back on. It tests good but is that the problem?
Thanks for any advice you have.
Do the temp sensors have any bearing on this problem?
Doesn't seem to run hot, pumps water good....


 
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Sounds like you have already thrown all the parts at it that it could possibly be. Except you didn't mention the #3 coil.
 
I replaced all the coils when I got it. Now I swapped 1&3 with 2&4 and same problem. I pulled the plugs and #3 I cleaner and oily probably from the miss but would the fouled plug make the plug wire not show fire on my timing light. Or is the miss coming down the line from power pack and timerbase? The last timer base I got rubbed on the flywheel on the top till I trimmed it a bit. I wish I was impressed with the timer base. The contacts on the inside rubbed on the magnets on the flywheel.
Am I overlooking an internal problem with #3?
I just got ngk plugs to try. The ones that were in it were closed and it looked like the piston hit them. The correct plugs are flat.
Scratching my head in California.
 
I will further explain. I received the from a neighbor that takes good care of his stuff. He had put new plugs in it when I got it, Also did a compression test. He has written 150-160 psi on all the heads. #1&3 plugs were ok. They were new so didn't check the others for a while. When I pulled them out the tab was bent down against the electrode. Not sure how it happened unless they were installed without the washer? I put new plugs in that had the tab over the electrode and they didn't hit but must be close.
I'm leaving now til Saturday, so I'll see what happens when I get back home.
Thanks for your input.....
One question. I compression tested dry and probably didn't get them fully pumped up. Is 150-160 too high for this motor? I read 120 is new....
 
A possibility----If the plug's ground electrode is mashed down against the center electrode it would short the incoming wire/spark to ground. So the inductive pickup on your timing light would see it as if you had connected it to ground and would not report it as a spark signal to the timing light.
 
The "flat" plug you state is actually called a "Surface Gap" plug. It's a cold running plug that is considered an alternative and is highly prone to fouling.

It's best to use the recommended Champion electrode type plug QL77JC4, gaping it at either .030 (long life) or at .040 (super hot spark).
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If the pistons of that engine hit the electrode type plugs as stated above.... you have a problem such as possibly having the wrong pistons installed, the cylinder heads shaved to excess, the block itself shaved to excess, or a combination of the three. If this is the case, either it's something you've had done and are aware of it... OR... a previous owner did of which you're probably NOT aware of it, but, in either case... it's a heart-breaker!
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When #3 spark plug boot is damaged (cut, ripped, whatever), the spark has been know to short out, jumping to the starboard hood latch, effectively knocking out #3 cylinder.
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Thanks again for the input.
I got this motor how it is.
Either it hasn’t hasn’t been opened since new or completely rebuilt since all the gaskets had paint on them like it had never been taken apart.
I’m thinking 1974... probably been overhauled and someone did something that I’ll either have to figure it out or maybe it’ll be the prettiest anchor in the Sacramento River. How long do I chase a motor of this age?
This motor has no corrosion, minimal wear and everything I open up looks good. Yes it’s a heartbreaker.
Im going to check and see if the right pistons got installed. Sounds most reasonable.
 
Also grounding to the latch seems reasonable I think. I’m going to try insulating it better. Now that I think back it did run a little different with the cowl off and plug wires moved....
#fishingforstrawsinca
 
sacriver runner said:
Either it hasn’t hasn’t been opened since new or completely rebuilt since all the gaskets had paint on them like it had never been taken apart.
Click to expand...

In my days at the bench... every engine I had rebuilt, with the block assembled, all openings were taped/plugged, and the powerhead primed and painted its original factory color before any and all of the cleaned accessories were installed. The end result was that the engine with the hood installed, it and the rest of the engine looked its age... BUT... with the hood removed, that powerhead assembly, including the hood pan looked like it just came from the factory.

Be sure to let us know about the spark plug hitting ordeal.
 
Ok, I talked to my neighbor and he said he bought the motor years ago and it came off a houseboat. It was very low hours, like 150 or so and now the hourmeter shows 350 but hasn’t worked for the last number of years. I would add that it has sat for the last 6 years without being used. He said it has never been rebuilt to his knowledge and when he check the compression this spring it was 125-130 on each cylinder.
On the spark plugs getting hit, I assume thats what happened. How else would the tab be bent next to the electrode? I only found this on cylinders 2&4 when I pulled those plugs. They were new so didn’t pull them out till I was deeply involved and had changed the coils already. I put new QL77JC4 plugs and they never were hit by the the cylinder. What made me question it was the high compression readings and the fact that when I screwed in the compression test fitting the cylinder hit it till I added another oring to seal it an space it out.
When I get home Monday I’m going to check spark wire grounding to latch on #3, and recheck timing. The repair manual says 4 degrees at idle and 26 WOT.
I’ll let you know how it goes.
I can’t thank you enough for the help. It will save me being the laughing stock of my family...!!!!!!
 
Watch this and you have idea of what needs to be done...
[FONT=Verdana,Arial,Tahoma,Calibri,Geneva,sans-serif]https://www.youtube.com/watch?v=w0Dxgw6RwlU[/FONT]
 
It’s been a while since I posted. I checked to make sure the timing was stable as per the video. It is firing correctly for each cylinder. I insulated #3 to keep it from grounding on the hood latch with some rubber and it seemed to help. It did run perfectly at 5000 rpm for about 5 min then started a slight miss which was on #1, by 10 min more it was dead. No spark at all on #1 at any rpm. I swapped coil wires 1&3 on timer base and cylinder and the miss moved to #3 and stayed there. Obviously the coil right? So I changed the coil, which was new a couple months ago. Today I had a chance to run it again. Now I’m back to the #3 miss above 4200 rpm. So I checked the timing at it was stable even with the missing cylinder at 26 degrees wot. As I retarded the timing the miss got better. I would reach back and retard the spark manually at wot and the miss would go away. At about 23 degrees and 4300 rpm the miss is slight. 4300-4500 is max rpm at that setting. At wot the spark is nonexistent on #3 at 26 degrees timing. By the way, I had another power pack that was basically new so swapped it out on the water. No change. The timer base is new a couple weeks ago. I tried a different spark plug, no change.

OK... now what? It seems the timing advance is losing #3.

Any advice is appreciated.....
 
You state above in post #18..... "No spark at all on #1 at any rpm. I swapped coil wires 1&3 on timer base and cylinder and the miss moved to #3 and stayed there. Obviously the coil right?"
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Wrong!..... If the miss moved with the timer-base wire, that indicates a flaw in the timer-base. However, you don't say that the move resulted in #1 coil firing.
 
I swapped coil wires 1&3 on timer base and cylinder and the miss moved to #3 and stayed there. Obviously the coil right?"

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Correction....
I apologize, I miss spoke myself. I changed the coil wires on the “power pack” (not timer base wires) and changed the plug wires to effectively swap coils on the 1 and 3 cylinder outputs from the power pack. The no spark followed the coil. So the timer base and power pack were working fine and the coil was the problem. I’ve been thinking. Could it be possible that #3 is grounding to the ground in the power pack? They are close to each other. Not sure the rubber seal is sealing the properly. Also in reading in the manual is says to cover the screws with black sealant on the power pack once wires are installed. It would hinder testing but could fix the grounding problem. I keep coming back that that is what it has to be. Everything else is new or tested. I did another compression test... 1 is 120, 2 is 110, 3 is 120 and 4 is 120. Should be golden.
 
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