1976 Mercury 110 (9.8hp) weird running issue??

justa150merc

Cadet
Joined
Jun 24, 2014
Messages
24
Good evening guys,

So I have a '76 Merc 9.8 that's in fantastic shape for its age. I bought it a year ago for $400 and have it really as just a small hobby motor that I occasionally throw on my great grandfathers old 12 foot boat and go bomb around the lake for a bit. I love old kiekhafer mercs!

Anyways, my problem is that during idle or lower throttle positions, the motor occasionally drops a cylinder and runs on one, but then as I start to increase the throttle, either slow or fast, the 2nd cylinder kicks in and it runs great everywhere from 1/4 throttle to full throttle. Hell, I get 22 mph out of her with myself and 3 gallons of fuel. It runs fantastic and always on 2 cylinders anywhere above roughly 1/4 throttle.

Once I get under 1/4 throttle, it's anyone's guess as to when it kicks out a cylinder again, sometimes it's right away, other times it runs on 2 for 5 minutes of low throttle then randomly kicks to 1.

I have checked to see which one is giving me issues and it appears to be the upper coil, if I pull that plug wire it runs on 1, if I pull the bottom wire it won't start. This is when it's going through its 1 cylinder routine. Like I said, sometimes it runs on 2 just fine for 5+ minutes.

I also hear a weird clicking noise with the cowl off when it kicks into 1 cylinder as though it's arcing and grounding somewhere??

Any thoughts would be great! I just bought a whole new (used) good working ignition system from a parts motor 76 9.8 that comes with coils wiring hardness etc. I'm thinking it's just a bad coil, but it's weird that it runs so good anywhere besides that 1/4 throttle and below. I can run it at WOT for 10 minutes and it doesn't miss a beat, same for other throttle positions besides 1/4 or lower. Thoughts????

Thanks again.

Background:
- always use 91 non E fuel with stabil mixed at 50:1 with pennzoil premium plus.
- carb is clean and adjusted
- brand new impeller that pumps water perfectly. Confirmed the motor is cooling properly.
- plugs were brand new last year
 
Last edited:

Mohawkmtrs

Chief Petty Officer
Joined
Jan 13, 2010
Messages
560
Sounds like a spark plug wire is shorting (arcing) out against something at less than 1/4 throttle.
 

justa150merc

Cadet
Joined
Jun 24, 2014
Messages
24
Sounds like a spark plug wire is shorting (arcing) out against something at less than 1/4 throttle.


I thought about that but its weird that it only arcs out a low throttle? you would think if it was a ground issue I would see it across the whole RPM range, no?
 

merc850

Commander
Joined
Jul 7, 2010
Messages
2,020
When you turn the tiller handle the trigger assembly under the flywheel rotates and one of the wires might be rubbing on part of the block causing a short in that position.
 

justa150merc

Cadet
Joined
Jun 24, 2014
Messages
24
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I thought about that but its weird that it only arcs out a low throttle? you would think if it was a ground issue I would see it across the whole RPM range, no?


Sounds interesting. I'll have to look into that and see if any wires are rubbing. Some of the insulation on the wiring harness running from switchbox that have begun to crack and has gotten hard due to old age. The picture here shows the harness that I am talking about. It's not my motor, but the red circle shows what I am talking about. Would that potentially cause my running issue? I ordered a used oem ignition assembly that included 2 coils, switchbox, and complete harness for only $60 off ebay which is in great condition.
 

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