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b86 75 hp problem

T

triple_trouble

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"Hello all,
This is my first

"Hello all,
This is my first post here. I have just come into possession of a 17' 1986 Blue Fin with a 1986 75hp Mecury outboard. The motor has been into a shop twice with no luck so my Father-in-law handed the boat to me. It starts great when cold and runs okay until warmed up. If you slowly give it throttle it runs through the revs okay until about 1800 rpm then it falters. Slowly give it more gas and at 2200 rpm it starts to die, the revs dropping off until it quits. If I give it a quick dab of choke as it starts to die then it goes like a rocket and runs flat out . After the motor is hot it becomes hard to start and won't idle. Any suggestions where to start looking? it seems to run on one carb when it is missing. Seems like an electrical problem except for clearing up when the choke is dabbed?"
 
"Could be an ignition problem.

"Could be an ignition problem. Have seen a cracked bobbin (winding) that loses continuity when it heats up.

In the 1800-2200 range it would be just starting to get power from the high speed coils, so my first set of tests would be on the stator.

It could be high speed windings going bad, plus a cracked bobbin...

Simple ohm tests can be done initially and followed up with DVA tests if the numbers are out of whack.

That particular model came with a few different stator combinations so I can't tell you off the top of my head which wires to test, but I can post it up once we know what you have there.

You should have either a blue, red and two yellow wires coming from the stator OR red/white, blue/white, blue, red and two yellows if the motor still has an OEM stator.

Normally, when trying to track down a possible heat related issue I will use the wife's blowdryer to heat up the flywheel (does an excellent job of mimicing a running motor)


Anyhow, post what you find for wires and I will throw up some tests for you.

If nothing else we can rule OUT the ignition..."
 
"It appears to have an OEM sta

"It appears to have an OEM stator as the wires are red/white, blue/white, blue, red and two yellows. I'll await the tests to perform. Many thanks,
Paul T"
 
"Here's the ohm chart - th

"Here's the ohm chart - the only thing I would do different is - #3 says if the numbers are bad, replace the stator - if the numbers are bad I would take into a shop and have it DVA tested just to be totally positive before I chucked the bucks for a new stator.

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"
 
"The reading between the red a

"The reading between the red and red/white wires was 146 ohms, slightly out of spec and no reading at all between the blue and blue/white wires. Have I found the problem?"
 
"Yes, no reading at all betwee

"Yes, no reading at all between the blues is a pretty good indicator that the stator is toast."
 
"I've ordered a new stator

"I've ordered a new stator coil which should be here by the middle of next week and we will take it from there. Thanks a lot for the advice and assistance Graham. If you need any help getting your old British motorcycle running give me a shout
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"
 
The new part has arrived and i

The new part has arrived and it tests out exactly the same as the one on the motor!
I'm out a few hundred bucks and no further ahead than I was a week ago.
 
Correct. No continuity at all

Correct. No continuity at all and it is a brand new OEM straight from Mercury. and it reads exactly the same between the reds as the original one 146.9 ohms.
 
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