'75 Johnson 115hp back-fireing

ohyeah829 · Mar 14, 2006

Ok, new problem....I've had my '75 Johnson 115hp engine idle for the winter. I winterized it by filling the gas tank and adding the de-waterizier....Is there anything special that I should have to do to get it running, now? Because, I can get it to crank, but it is backfiring now. Both when in neutral and in gear. The only thing that I did over the winter is replace the spark plugs. I have noticed that if I put my finger on the spark plug wire while the engine is running, it will shock me, duh...but I can feel it sherper when it backfires...like a needle poking. This is probably usual, huh?? Any solutions?

B.autry4711A · Mar 14, 2006

Re: '75 Johnson 115hp back-fireing

Ohyeah829, Double check your spark plug wires. You said you changed out spark plugs over the winter. You might have crossed over a spark plug wire when installed those new spark plugs. trace your upper 2 spark plug wires back to the top coils and do the same with the bottom 2. None of them should cross each other.

JB · Mar 14, 2006

Re: '75 Johnson 115hp back-fireing

Backfire? Is that a loud BANG from the exhaust or is it a pop from the intakes? If it is a BANG you have a timing problem. Can be from switched plug wires, sheared flywheel key, loose stator or interfeed in the powerpack. If it is a pop (we call that a sneeze) it is too lean from at least one carb throat. Good luck.

ohyeah829 · Mar 14, 2006

Re: '75 Johnson 115hp back-fireing

Ok, none off the plug wires are crossed. Double checked. And, it is more of a "cough" as you say. No bangs...but if it idles long enough, the engine will die. Also, I noticed that the lower unit will smoke a little from the exhausts on each side. And, the lower unit is a little warm. Is this normal? And, what does it mean "too lean"? Is there something I can do to fix the problem?

ohyeah829 · Mar 14, 2006

Re: '75 Johnson 115hp back-fireing

Also, someone else suggeted changing out the fuel. I believe this will help, too.

ob · Mar 14, 2006

Re: '75 Johnson 115hp back-fireing

Lean as in fouled restricted carburetors.If it has set out of use for a good spell(particularly with aged fuel mix) ,it is likely that one or more of the carbs are in need of dismantling and cleaning of all fixed orifices and ports.Very critical as a two stroke relies on it's fuel mix to provide cylinder lubrication as well.

ohyeah829 · Mar 14, 2006

Re: '75 Johnson 115hp back-fireing

Can I do this or is it too critical and should be sent to the shop?

rickdb1boat · Mar 14, 2006

Re: '75 Johnson 115hp back-fireing

Are you saying that you touch the rubber part of the spark plug wire while it's attached to the plug and it shocks you??? If so, you may have an errant spark juming from the wire to ground. Try running it at night on the muffs and see if you spot stray sparks anywhere...

ob · Mar 14, 2006

Re: '75 Johnson 115hp back-fireing

With some basic skills and a manual to use as a guide ,many people perform their own carburetor service.The manual will also touch on some of the finer final adjustment points of the carburetor linkage as well.Always a good idea to store with fresh fuel mix in the off season and run the engine whenever possible to prevent carb fouling.

ohyeah829 · Mar 14, 2006

Re: '75 Johnson 115hp back-fireing

Ok, first: Yes. I touch the rubber sleeve over the plug and I feel a shock...not normal? Didn't think so. Now, these are not the wires that I can just replace. They are....how do you say it...connected... Second: Do they make a manual specific to my engine? Or, just abroad? And, before winterizing it, I did fill the tank with fresh gas/oil and stabilizer.

ohyeah829 · Mar 15, 2006

Re: '75 Johnson 115hp back-fireing

Any ideas on a manual? What should I do about the plug wires? Also, why would the lower unit be running warm? Normal? Thanks for all your help!

ezeke · Mar 15, 2006

Re: '75 Johnson 115hp back-fireing

You can buy the OMC factory model-specific service manual from Ken Cook Company. Check the model number here: 115 Johnson Model Guide

Cricket Too · Mar 15, 2006

Re: '75 Johnson 115hp back-fireing

When you filled your tank and put stabilizer in it, did you run any of that stabilized fuel through the engine in order to have stabilized fuel sitting in your carb bowls while it sat? I usually run stabilized fuel through my carbs for a good 10 minutes or so before the winter. Also, not that this has anything to do with your carbs, but did you fog this engine at all before it sat, that's usually a good idea. The lower unit getting warm is normal, that is where the exhaust exits the engine, and exhaust is hot. The L/U should not get exteremely hot to the touch, just warm, you should be able to hold your hand on it. You are saying that the plug wires are connected to the coils and cannot just be removed, but you can buy kits that you can use to replace the boot at the plug end and make a good new connection. Definitely try running it on the muffs at night first and see if you see any spark jumping around.

ohyeah829 · Mar 15, 2006

Re: '75 Johnson 115hp back-fireing

Great! I appreciate the advice. Ok, when I run it @ night, if I do see it sperking, what then? Is this a problem or just a sign that it's time to replace the plug "boots"? And, yes, the lower unit is just warm, not hot...but I had an engine lock up on me before so I am trying to be cautious.

'75 Johnson 115hp back-fireing

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