1984 mercury 90 hp inline 6 bogs with throttle

larboc

Seaman
Joined
Jul 26, 2001
Messages
61
just got off the lake and i'm not happy.

I never ran the motor after I bought it because it was supposed to need exhaust baffle gaskets. I replaced the gaskets (filed down the ridge) and end seals with genuine merc parts. Looked into exhaust ports during this and they looked like new. pistons still had very obvious machining marks, no signs of scuffing.

Motor fires right up and idles a little rough but seems decent.

In neutral I give it wot and it slowly revs up to 5k ish but that's it. It seems like I can hear cylinders coming on and off like they are intermittently firing, almost sounds like a sluggish rev limiter.

In gear it will only rev enough for a fast troll but sounds like it is working really hard, again the cylinders are hit and miss. They will fire for a couple revolutions, then miss for 2-3 seconds. Cylinders aren't firing.

I cranked it with all the plugs out and they all were all firing. Carbs look to have recently been rebuilt.

I advanced the timing at 3/4 throttle to wot advance and farther and it seemed to run a little better. I also tried turning the flywheel one bolt set counter clockwise and then it seemed to really run better. I looked through the top and bottom carb and they looked fine. all carbs have fuel when the jet cover is cracked open.

Holding my hand over any of the three carbs will wet my hand with gas and slow down or kill the engine.

I don't know what's wrong, my only guess is I don't have something wired right with the wiring after I put the power head back on, or a power pack is bad.

as far as I know I put everything together right after the rebuild. Does anyone have a link to the wiring diagram for the motor? or a mercury power pack troubleshooting guide?

thanks for any help.
 

larboc

Seaman
Joined
Jul 26, 2001
Messages
61
Re: 1984 mercury 90 hp inline 6 bogs with throttle

Ok, so it revs up to about 2500 on all cylinders. Then all cylinders drop out except for #4. I tried swapping the stator power leads and no change. The stator resistance is within spec according to http://www.outboardignition.com/page27.asp

I don't have a dva for my multimeter so I can't check running voltage at the stator.

This motor has the early switch boxes i guess that don't use an idle stabilizer. according to this wiring diagram http://forums.iboats.com/showthread.php?t=324375&highlight=mercury+inline+wiring the ones with the stabilizer seems like it has a ground going to the bias jumper, however I have nothing attached to the jumper. i tried grounding the jumper and it changed the way the engine ran but not for the better really.

help, somebody!
 

larboc

Seaman
Joined
Jul 26, 2001
Messages
61
Re: 1984 mercury 90 hp inline 6 bogs with throttle

Ok, turns out the regulator is bad. I disconnected it and problems went away.
 

larboc

Seaman
Joined
Jul 26, 2001
Messages
61
Re: 1984 mercury 90 hp inline 6 bogs with throttle

New regulator has the same problem. Bad stator? I tried rotating the stator and it made no difference.
 
Joined
Feb 21, 2009
Messages
58
Re: 1984 mercury 90 hp inline 6 bogs with throttle

You can remove the idle stabilizer, it is a bad device, you don't need it. It is more than likely your whole problem. But with those Mercs it could be many different issues. Have you had the carbs rebuilt recently? I do mine once a year. After the rebuild, have a link and sync done.
 
Joined
Feb 21, 2009
Messages
58
Re: 1984 mercury 90 hp inline 6 bogs with throttle

Never Rev your motor that high, those 2cycle motors need to have a load on them when at those speeds. The best way to work on the motor when testing is in the water.
 
Joined
Feb 21, 2009
Messages
58
Re: 1984 mercury 90 hp inline 6 bogs with throttle

I read your other post, It sounds like you need to take it to a shop and have a link and sync done on it, probably will only set you back about 100 to 150 dollars to have done, and will make a world of difference. Just wondering , what is the compression readings on all 6 cylinders.
 

larboc

Seaman
Joined
Jul 26, 2001
Messages
61
Re: 1984 mercury 90 hp inline 6 bogs with throttle

I appriciate the advice, but I don't see how fine tuning the timing curve would affect loss of spark when the regulator is connected. I am suspect of the stator. Does anyone know how to check and make sure the stator is properly oriented?

The odd thing is that the stator checks out when I do the ohm tests to it and it makes 18ish volts at idle when disconnected from the regulator.

I also don't understand how the load on the charging coil is affecting the ignition windings.
 
Top