Proper coil testing

[wheelers4life]

I have a 1998 mercury bigfoot 50elpt 4s. Runs great on muffs. In the water idles fine. Runs fin for a about 20 min the shuts off and wont start for about an hour. I thought the carbs were flooding. I cleaned the carbs with a ultrasonic cleaner and balanced the cards. Took it out on the water and same thing. I pulled the coils off. I'm getting a reading of .4 ohms across the positive and negative wires on the coil. When I try across either the positive or negative and the spark plug wire I do not get a reading at all. The spark plug wires are permanently connected to the coil. Looks like they are glued in. Any help would be greatly appreciated. I have tried the search feature and cannot find anything on this application.
thanks

 

[wheelers4life]

I have taken it to our local mechanic and he cannot reproduce the results.

 

[Chris1956]

Normally ignition coils would have a near short across the primary winding, which is what you are seeing. They also should have a high ohm (10K??) across the secondary winding (positive connection and the spark plug lead).

So if the secondary winding is open (rare in my experience), the coil is bad.

A better test is to crank the motor with the spark plug in the boot and held against the block of the motor. If she sparks blue and snappy, the coil and plug are good.

 

[wheelers4life]

Ok thanks I will try that

 

[wheelers4life]

Any ideas why this outboard would die after a few minutes on the water then not start for an hour.

 

[Chris1956]

After it dies, check it for spark. If none, maybe switchbox is susceptible to heat.

 

[Faztbullet]

Stator or ECU as no switchbox

 

[wheelers4life]

So far today one hour and still running. But wot is only 3500 rpm and 9 mph. Could I have balanced the carbs to low. I have my rps at 900 idle in the water. Not in gear

 

[Chris1956]

9 mph at 3500 RPM is unusual. Is prop slipping (spun) or real damaged? Maybe tach is very wrong?

900 RPM at idle is a bit high.

 

[wheelers4life]

No prop is ok. I'm thinking maybe when I balanced the carbs, I'm not getting full open butterflies. This boat has always seemed to idle high. When I cleaned the carbs. I put them back on and put my synchronizer on. The metal rodes were all crazy. I just adjusted them level and idled it down to 1000 on the muffs. In the water it idles at 900. And has been running good all day. Just cant get back to my 5600 rpms and 16 mph like before.

 

[wheelers4life]

Now it wont start

 

[wheelers4life]

It is starting but as soon as I hit the throttle it dies. I just pulled the plugs and I'm getting spark out of all 4. This thing has got me wooped. Guess back to a different shop. The last 2 could not find anything wrong with it. This just does not make sense

 

[wheelers4life]

Well I'm off to a Fort Phantom Marine to drop it off. He said the are 2 weeks out. I will let you guys know what he finds, if anything