No spark condition

[treehan]

I have a 1986 Wellcraft with a Merc in it that won't start. Here is the engine info from the tag on the engine:
Mercury Marine Division
model: MCM 140
181 CID
Serial # A541917

I am stuck with no spark condition. Need help discerning what to do next. I looked at the coil, which is pretty rusty. It has on the + terminal: red w/ yellow stripe wire coming from the starter solenoid and a purple wire that i believe is coming from the electric choke by carb. The - terminal has a black wire running to the underside of the distributor and then a white or maybe gray wire coming from god knows where. Not sure what that is supposed to be. Anyway, I get no spark at all and the purple wire that is coming from the choke gets VERY hot. Smoke and everything if i try to start it for a while. Some information I have gathered seems to say that the purple wire is a resistor wire. Service manual says it should read 1.8-2 ohms, I get like 1.6. Should i start be replacing this wire? Is this correct and what voltage readings etc should I have at the coil? It is showing only 5-6 V across the + and - terminals now. Any help would be greatly appreciated. Can't figure out how what / how to test the coil or what specs it should be. I took it off from the bracket because I wanted to see a part number, but it is apparently worn off except for the last "03".

 

[Don S]

Re: No spark condition

Have you changed the points? They get glazed over and won't fire.

1.6 ohms is fine.

 

[Fishermark]

Re: No spark condition

Like Don - I too would suspect points first. The wire getting hot... maybe just from continued cranking? A loose or corroded connection can create heat as well.

The white/grey wire on the negative side goes to your tach and the black wire goes down to your points.

You might try disconnecting the white wire and see if that helps. I've seen where a short in the tach can create problems as well. It would eliminate one thing to check.

 

[treehan]

Re: No spark condition

okay am taking out condenser, points and rotor etc. for new parts-- if i can find them. the label on the distributor is worn off so i don't know what number it is. it MIGHT say SAE 11171 or somethign close. will try with new points. is it typical for the stationary point to have a hole in it through the middle? i also checked and have 12v at + side of coil and when i put my meter on the dist. side of the coil wire, 12v + there too. never worked with points before (even my '70 monte carlo had been upgraded to hei!) so i don't know how to set/adjust them either.

 

[Bondo]

Re: No spark condition

so i don't know how to set/adjust them either.

Ayuh,...

Up in the Aduts Only section at the top of this forum you'll find links to the factory service manual for your motor,+ drive...

 

[treehan]

Re: No spark condition

cleaned the points, rotor etc. still no spark. i am now baffled. like i said, +12v to coil, and out of the coil to distributor. then no spark on any spark plug wire. nobody seems to have the dist. parts in stock here, so i used my dremel and polished them u nice just to see if i could get any spark. not a chance.

 

[Maclin]

Re: No spark condition

You will WANT to get new points installed correctly before you want to run it on the water.

You can see if the coil works or not easily enough. Remove all wires from the Neg coil post. Hook a different long wire to that post. Take the coil wire off the top of the distributor cap and get it close to a ground somewhere so you can see it, may need to poke a screwdriver into the end of it and lay it close to a ground. Turn the key on and ground and unground the long wire from the Neg coil post by tapping it on a good engine ground. This should produce a spark out of the coil wire. This tests the voltage to the coil and the coil. If this works then you know the problem is inside the distributor. If no spark this way then the voltage to the coil is missing or the coil is bad.

 

[treehan]

Re: No spark condition

ok so i found a new coil at autozone and now the boat has spark. yay. runs pretty rough though, will have to get new points, condenser, cap, etc. i guess. thanks for all of your help guys!