Do I have a bad coil?

NYT

Cadet
Joined
Jul 13, 2009
Messages
14
Hello.I have a 1985 15hp Yamaha SK motor.I just got through putting in new rings and pistons and rebuilding the carb.I have good compression and good fuel delivery.I started the motor and noticed water leaking out the head gasket so I shut it off and removed the head and cleaned both surfaces and reinstalled it.Now I have no spark.I checked the cdi box and I think it's ok. When I check the ignition coil with a meter the numbers do not match the manual. When I test from one spark plug boot to the other the manual says it should read 2800-4200 and I'm getting .04.When I test the two leads coming out from the coil the meter swings to zero.I get these readings using a analog meter set at rx1.When I use a digital meter set at 200 ohms I get the opposite results but the same numbers.Meaning I get a reading when testing the leads and none when testing the boots. Regardless of the difference between the two meters I think the coil may be bad but I've read other post's that say the coil rarely is the culprit.Before I go and spend $100 on a new coil I just wanted to check with someone else who has more experience in this area.Thanks for the help.
 

waffles1

Petty Officer 1st Class
Joined
Jul 15, 2008
Messages
260
Re: Do I have a bad coil?

Make sure you didn't lose a ground some where when you removed the head. A weak or no ground could cause this.
 

NYT

Cadet
Joined
Jul 13, 2009
Messages
14
Re: Do I have a bad coil?

This coil does not have a lead that goes to a ground.It just has an orange and black lead that plugs into the cdi box.I tested it according to the manual that showed the leads unplugged from the box.I actually have the coil off the motor and am testing it at my bench.I really don't know how it's grounded.
 

rodbolt

Supreme Mariner
Joined
Sep 1, 2003
Messages
20,066
Re: Do I have a bad coil?

it grounds throgh the CDI, place your digital meter in the auto ranging function and rerun the test.
always make sure your scale settings are the correct scale settings for what you wish to measure or use my friend otto :).
 

NYT

Cadet
Joined
Jul 13, 2009
Messages
14
Re: Do I have a bad coil?

Thanks for the advice guys.I have 3 meters and none of them are auto ranging.I guess I need to go and buy a 4th.
 
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