'74 Johnson 15 Skipping

tysonnathan · May 6, 2009

1974 Johnson Seahorse, 15hp:

This motor was given to me and it ran very poorly when I got it. I have done some work on it over the past year or so and it is running ok, but I have a skipping issue that I haven't been able to get straitened out.

I had some other issues as well but got them pretty well fixed.

Parts I have replaced:

spark plugs
ignition coils
tune up kit:condensors and points
fuel pump
cleaned and rebuilt carb

The motor is runnng a lot better, but it is still skipping at times. The skipping seems to get worse the longer I run the motor. Almost always cranks on the first pull or two. Runs well for a while, but eventually starts skipping at slow speeds. Doesn't want to idle. Really skips bad at low to mid throttle when the boat is kind of plowing. The skips start and stop every few seconds sometimes. When I am accelerating from a stop, it will start to skip at mid to low throttle, but if I just hold the throttle there, it will often start running on both cylinders and take off. I don't know what else to replace on the ignition system. Any ideas?

56 rude · May 6, 2009

Re: '74 Johnson 15 Skipping

your pretty close to my 1976 15hp evinrude,look very closely at the coils,your looking for hairline fractures,anything out of the ordinary,replace!

tashasdaddy · May 6, 2009

Re: '74 Johnson 15 Skipping

linc & sinc so timing advances properly with the carbs,

56 rude · May 6, 2009

Re: '74 Johnson 15 Skipping

follow tashadaddy,s advice and if that doesnt work go back to the coils even though their new (arnt they).also make sure even though you replaced the plugs they or should i say one of them may be failing .plugs are cheap !

tysonnathan · May 7, 2009

Re: '74 Johnson 15 Skipping

The coils are brand new. I have looked over them and they are fine. I will try to synchronize the timing and carb and see what that does.

crxess · May 7, 2009

Re: '74 Johnson 15 Skipping

tysonnathan said:
The coils are brand new. I have looked over them and they are fine. I will try to synchronize the timing and carb and see what that does.

Still.............. take a look. could be that a wire is fraid. reckeck/clean points. clean/tighten all connections. Make sure wires are well clear of moving parts.

tysonnathan · May 18, 2009

Re: '74 Johnson 15 Skipping

crxess said:
Still.............. take a look. could be that a wire is fraid. reckeck/clean points. clean/tighten all connections. Make sure wires are well clear of moving parts.

I have checked and rechecked all of the electical components from under the flywheel to the cylinder. The points, condensors, coils, plugs etc are all brand new. The point gap is dead on. All the wires look good. I have even ran the motor on the stand at night and checked for a short in a coil or wire by looking for a spark (thats how I found out the coils were bad to begin with). I am hopeful that synchronizing the carb and spark will work. I feel like I have ruled out just about everything else...

Thanks for the help guys... I will post back after I sync.

tysonnathan · Jun 20, 2009

Re: '74 Johnson 15 Skipping

Alright guys.... Just got some time to tinker with this motor today. I have not synchronized it yet (need to get a manual for instructions). I cranked her today, just to look over all the wires/coils/etc. one more time. Everything looked good. I then ran my hand over all the ignition components to feel for a short that I couldn't see. When I got to the spark plug I got a pretty good shock! When I touch the hex part of the top cylinder spark plug I get a shock. I switched the top and bottom plug to see if it was a bad plug, but it still only did it on the top cylinder. Does anybody know what is going on here?

tysonnathan · Jun 20, 2009

Re: '74 Johnson 15 Skipping

I switched the coils and the problem moved with it. I guess the new coil is no good???

OptsyEagle · Jun 20, 2009

Re: '74 Johnson 15 Skipping

I will throw in my 2 cents, but most people think I am crazy. I have a 1975 9.9Hp Evinrude which is pretty much the identical motor except for the carb. You call it skipping, I call it surging and bogging but perhaps it is the same problem (if not, ignore my opinion).

The recommended plugs for this motor are champion UL81C plugs if I recall correctly. My motor hates them. I tried multiple sets of these plugs and got the problem of the motor surging forward, then bogging down, then surging again, like a cylinder was intermittently failing and firing, on and off again.

I replaced the spark plugs with NGK B7HS and have never had the problem again. It makes no sense to me either, but that was my experience. I didn't even believe it myself, so I constantly put back the UL81C's and the problem returns. I do not do this anymore. I just use the NGK's.

Don't get me wrong. I use champion plugs on other OMC motors without any problems but the 9.9/15 HP Evinrude/Johnson's from 1974 to 1976, seem to really hate them. Good luck to you.

tysonnathan · Jun 20, 2009

Re: '74 Johnson 15 Skipping

Thanks OE.. I am currently running NGK plugs, as I prefer them as well. I might try replacing, although they probably only have 2 or 3 hours on them. Right now my biggest quandry is why the hex part of the spark plug is shocking me... Perhaps the plug doesn't have good contact/ground with the motor?? It seems that if the plug base had good contact the whole motor block would shock me... not just the plug base...

tysonnathan · Jun 20, 2009

Re: '74 Johnson 15 Skipping

On second thought, its probably not the ground... When I switch the coils, the problem moves with them. Each of the plugs works fine when hooked to one of the coils.

Rick. · Jun 20, 2009

Re: '74 Johnson 15 Skipping

I can't see how a coil could cause this shock thing. Is it only when you touch the hex part? Have you tried holding your fingers on the insulator and at the very end of the plug wire boot? Are booth coils wired the exact same on the magneto? When I first started reading your post tonight I was thinking perhaps your running the slow speed needle a little lean and that's causing it to sneeze but now I'm really stumped. Rick.

tysonnathan · Jun 20, 2009

Re: '74 Johnson 15 Skipping

Im stumped too, Rick... With the plugs installed and the wires hooked up to the plugs, I get shocked when I touch the hex part of the plug. If I switch spark plugs,. the problem remains on the same cylinder. However, if I switch the coils around, the other cylinders plug gives me a shock. As far as I know the coils are wired the same way to the magneto. The coils have connectors that just plug right in. The plug wire has good contact to the plug abd pushing on the boot makes no difference.

Also, the motor might run a tad rough while I am testing it at idle, but it is definately running on both cylinders. It is shocking me and sparking at the same time... It may be totally failing, intermitently, when under load causing the skipping symptom that I often get when I run the boat in the water.

Hope someone can shed some light on this...

iwombat · Jun 20, 2009

Re: '74 Johnson 15 Skipping

When you're moving the coils are you moving the plug wires along with them? My guess is it's arcing from the plug wire to the spark plug ground.

Rick. · Jun 20, 2009

Re: '74 Johnson 15 Skipping

I wasn't thinking about the connection to the plug wire from the coil. I was wondering if the other coil connections are wired exactly the same for each one. Rick.

tysonnathan · Jun 21, 2009

Re: '74 Johnson 15 Skipping

Both coils are wired the same under the flywheel... I am moving the wires along with the coils.

Rick. · Jun 21, 2009

Re: '74 Johnson 15 Skipping

Wrap the boot real good with elec. tape and close off the end of the boot at the plug insulator. Then see if that stops the shock thing. This is a temporary thing to determine if the spark is leaking past the boot. Another thing I have done is fired my motor in the dark. Any spark leakage is much easier to see in the dark. Rick.

tysonnathan · Jun 21, 2009

Re: '74 Johnson 15 Skipping

Alrighty guys. Just tinkered with her a little more. The problem is following the plug wire boot, not the coil. I got a wire with allogator clamps and grounded it to the block. I then put the other end on the hex part of the plug. When I did this the spark jumped to it. The other plug would not do that. I then put the ground wire on the outside of the boot. When I did this, the spark appeared to jump through the rubber boot, not around it (crazy, I know). I even touched the ground wire to the outside corner of the boot (farthest from the open ends of the boot) and the spark jumped right through the rubber. When I switched the boots, the problem moved with the boot. It appears that the boot conducts electricity!...

When I bought the coils, they only had one in stock at the marina. I bought the other one from iboats (at a much lower price I might add). The one I bought from iboats is working fine. The one from the marina (which is a name brand) is the one that is failing.

I am going to try to get a new boot from the auto parts store. Should fix me up. Thanks for the help guys!

TN

Rick. · Jun 21, 2009

Re: '74 Johnson 15 Skipping

Good to here your back on track. Try to get a boot from an OMC dealer if you can. They are a stock item and made to fit the wire size of your motor. To remove and install boots it is my experience that soaking them in hot water for a minute makes them far easier to work on. Rick.

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