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Author Topic:   Spark Plug Wires
jimh posted 08-13-2001 11:47 PM ET (US)   Profile for jimh   Send Email to jimh  
This information may be useful if you have an older outboard engine!

In the process to running my new (used) boat for the first full season, I have found one problem that is simple to cure: loose spark plug wires.

I first became aware of the problem when one of the engines suddenly decided it would not run at over 2500 RPM in the middle of Lake Michigan. We limped to shore (about ten miles away) and found the problem as soon as the cowling came off the engine: a spark plug wire had fallen off a plug, so we were running on two cylinders instead of three.

This episode made me aware of the need for checking the plug wires. On our last cruise (9-days of living aboard), I got into a routine of yanking the shrouds off the engines every morning to check them over, paying special attention to the fit of the plug wires. I found that several of them were coming loose after a day of hard boating and running 70 miles or more.

I cured this problem with some Ty-Raps. A plastic ty-rap around the boot of the plug rubber insulator increased the firmness of the fit so the plug wires stayed in place.

One nice thing about boating with some mates: I borrowed the ty-raps from them! LHG had a handful in his boat toolkit inventory. (I had several hundred in the trunk of my car about 200 miles away--not much good there!) Larry also commented that the Mercury mechanics had used them on his engines to retain the wires at the coil end of the circuit. Mine seemed well seated in the coils, but they did not like to stay on the plugs.

I also wonder if the tendency for the boots to come off the plugs might be due to someone having used a silicon grease on them. I know in automotive applications it is often recommended that the rubber boat be lubricated with a silicon grease, otherwise the boot may end up bonded to the plug after 50,000 miles. In that application the plugs are usually buried in deep wells and the boot is subject to a great deal of heat from the surrounding engine block.

In marine applications--at least mine--the plug and boot are in open air, and I doubt that any silicon grease is needed. In fact, I think it would not be a good idea to use it because of the problems I mentioned above.

Fresh plugs, properly gapped, and with the boots well seated, really make the engines start and run much better!


Hank posted 08-14-2001 12:05 AM ET (US)     Profile for Hank  Send Email to Hank     
Good point about spark plug wires. Easy thing to take care of and so important.

On my old (1984) Evinrude I've found it necessary to replace or repair some of the wires because the coiled metal clip in the boots disconnect from the ignition wire. I carry some of the clips and extra ignition wire in my tool kit.


ValkariaKid posted 08-14-2001 02:00 AM ET (US)     Profile for ValkariaKid  Send Email to ValkariaKid     
Another good idea is to take a pair of needle nose pliers and pinch the metal connector inside the boot. This will result in a tighter fit.

A little dab of dielectric tune-up grease is still a good idea if you pull your plugs often. Alot of plug wires have been ruined by tugging the wire as opposed to the boot when removing them leaving the connector still on the plug tip.

The boot was not meant to secure the wire to the plug. That's the job of the connector inside the boot. The "click" you hear when you install a plug wire properly is the connector snapping onto the plug tip.


Whalerdan posted 08-14-2001 08:09 AM ET (US)     Profile for Whalerdan  Send Email to Whalerdan     
Thanks for the tip. I had a similar situation after running hard one day. Like you said found it as soon as the cowling came off. Will give the zip ties a try.
Bigshot posted 08-14-2001 09:57 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
My Yamaha 90 likes to squeeze off plug wires so I did the stips on it. Do NOT put them on very tight because then you can't get them back on once you change plugs. Just snug them up and they will last forever.
bigz posted 08-14-2001 10:29 AM ET (US)     Profile for bigz    
JimH the plastic ties are a great idea over the old racing method of wiring them up! Guess back then when that started didn't have the plastic ties.

The thing is when you needed to change plugs you un-did and saved the ss wire to reuse, real bitch to do.

We have the 2- 200 Yamaha plugs wired, think we'll change to tie wraps if they don't melt :) Tom

triblet posted 08-14-2001 10:49 AM ET (US)     Profile for triblet  Send Email to triblet     
My 1997ish Evinrude 90HP specs greasing the
boots. I think it's to keep water out.


jimh posted 08-14-2001 02:46 PM ET (US)     Profile for jimh  Send Email to jimh     
Thanks for all the comments on the plugs.

I will look at the clips inside the boots, too. I think that often happens is that the spring characteristic of the metal is lost when it gets hot from arcing that is occuring inside the boot. When the metal electrode of the boot/wire gets loose, it probably arcs inside the boot. This heats up the metal and causes it to loose its spring.

Using the ty-wraps was a fast and simple cure. I will look into the heat rating of the ty-raps, but they are nylon and the plug boots should not be that hot.


Bigshot posted 08-14-2001 02:50 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Jim, mine have been on there for years.
andygere posted 08-14-2001 07:19 PM ET (US)     Profile for andygere  Send Email to andygere     
A sparkplug wire puller is a great tool for removing stuck boots, available at any autoparts store for a few bucks. I use mine every time I remove the wires. Also check the threaded electrode if your plugs are that type. They can and do vibrate loose. Finally, check the plugs themselves. I had one vibrate loose, less than half a turn, but enough to make the cylinder lose spark/compression and cause the motor to run rough.
Alioop posted 08-14-2001 09:30 PM ET (US)     Profile for Alioop  Send Email to Alioop     
Jim,I had the same probelm on my 1986 70 horse Yamaha,the metal terminals where tight and snapped on to the plugs but the vibrations would cause the wires to fall off once in a while. I checked into replacing the wires but found out they come free with a new coil,only way you can buy the wires. The new coils come with updated wires with differant spark plug ends(same as on my new 70hp Yamaha)I did not purchase these as I did the same as you and ran that motor like that for 10 years with the same tie wraps on them.
jimh posted 08-14-2001 11:51 PM ET (US)     Profile for jimh  Send Email to jimh     
Interesting about the '86 Yamaha. Mine are 1987 Yamaha 70's; they don't like to keep the plug wires in place either.

Perhaps Yamaha became aware of this problem and changed to a different style boot.

The plugs "snap" into place on the metal connectors, but they tend to work loose.


SWarren posted 08-15-2001 09:00 AM ET (US)     Profile for SWarren  Send Email to SWarren     
My 87 yamaha on my montauk came lose alot also. The mechanic told me to replace the wires with OMC ones. He said the would not come loose on the plugs. I never tried it though, so I cant say if it would work.
Bigshot posted 08-15-2001 09:50 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Have only heard of this with Yamaha's, Actually mostly on the 70's & 90's. Maybe the shroud hits them or something.

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