HELP...is it the coil?

My 15 yr. old son is getting his new/old boat ready for this summer and has bought a 1977 85hp. Johnson Javelin. The party he bought it from said it runs fine until it gets real warm and then it will lose power and will not plain out. Sure enough this is exactly what happened on his first trip out. A mechanic has told us it could be the coil? How many coils does this motor have and are they hard to replace. We will have to do it ourselves due to his bank account.

Thank you

Re: HELP...is it the coil?

There are 4 coils, 1 per cylinder. Just follow the spark plug wire and you will find the coil. You can get them here on I-boat relatively cheap.When you remove the coil use some sandpaper and really give the mounting area a good cleaning for a good ground.

Re: HELP...is it the coil?

when it looses power what does it sound like.
Does it bog down or start skipping, sputtering etc.
It could be a number of things.
Ususally a bad coil will make it run like crap if it is has heat problem.

it could be a fuel resrtiction too.
basically anywhere from the fuel pickup in the tank all the way to the carb jets could cause an issue.

after it heats up and looses power if you let off the throttle does it idle ok?
if so i would check the fuel system for issues.

in the FAQ area there is a good article on decarbing (removing the carbon buildup fron the cylinders and rings) it may not be a bad idea to decarb it first and check the compression on all cyliners.
they should be very close readings on all cylinders.

Re: HELP...is it the coil?

ok let's do some trouble shooting before we start buying 4 new coils. 1st check the compression on all cylinders, should be over 100 psi, and with 10% of each other. take it out, run it till it acts up, remove the cowl, and touch the engine block just above the the cylinder heads, you should be able to hold you finger there for 2-3 seconds without it becoming extremely uncomfortable. now take one spark plug wire off and put so it won't ground, try taking off. then put it on and do the next onetill you have done the all. if there is a change note which one, that may be the culpret. if it is the same on all plugs, you can rule out the coils, and power pack. now going back if the one that had the change, carefully noting where all the wires go, completely swap coils with another cylinder. if the problems moves with the coil, the coil is bad. if not it's time to test the power pack. do this and get back with us. don't throw parts at it, it doesn't need. it will also teach him how to troubleshoot a problem.

Re: HELP...is it the coil?

Use a portable tank with fresh fuel and oil and a different fuel line and bulb. That will confirm if there is a problem with the fuel source.

Check to be sure that the overheat warning horn is functioning by disconnecting the tan wire at the cylinder head and grounding the control end with the ignition key on. The disconnect is under a sleeve, a few inches from the cylinder head.

If any of your ignition coils are cracked, discolored, or melted, you may want to replace them. You may be able to replicate the problem by heating the coil with a hair dryer. If the coils are bad, they can damage the power pack.

The 1973-1977 V4 motors run with very high voltage in the ignition sytem, they will not function properly on automotive spark plug wires. Run the motor in the dark if you can, to look for arcing around the plugs and wires. It is a good idea to disconnect and clean all of the ground wires.

Re: HELP...is it the coil?

Thanks all for responding...here is a little more info. When it starts acting up it idles perferct and starts instantly. It however only pushed his 16ft. Glaspar which is pretty light in weight 23mph before the motor acts up. I think this motor should push it around 35+? It does drip a little black oil off of the bottom of motor after running, is this carbon?

Re: HELP...is it the coil?

tashasdaddy could you please explain the taking off of spark plug sequence. Do I take wire off and take spark plug out and put wire back on?

Thank you

Re: HELP...is it the coil?

I think he meant to just pull off the spark plug wire one cylinder at a time. By doing this it will help minimize your problem. Hopefully pinpiont the problem.

Re: HELP...is it the coil?

While running rough, removing the spark plug wires one at a time may show that with one of the plugs there will be no change.

Often, a ignition coil that is breaking down under heat wiill also be either cracked, discolored or partially melted.

Re: HELP...is it the coil?

If that engine is pushing the boat 23 mph before acting up, it is acting up, just not as bad. Do a compression test first. Then check out the fuel, and ign. system, along with checking the sync. & link.