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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 11073
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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1982 Evinrude 25 hp. Idle is good but misses badly at speed.

Customer Question

1982 Evinrude 25 hp. Idle is good but misses badly at speed.
JA: Sometimes things that you think will be really complicated end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Tell me a bit more about what's going on so the Marine Mechanic can help you best.
Customer: The boat has been sitting for a while. I rebuilt the carb, replaced the primer solenoid, starter. Took it to the lake and it ran good until the starter came loose, my bad. I disassembled the started mount and made repair, but now misses badly at speed. I suspect I messed up the timing.
JA: Sometimes boat issues seem like they'll be really complicated, but end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Is there anything else important you think the Marine Mechanic should know?
Customer: No, fuel is clean and mixed at 50-1, new spark plugs, ans new water pump impeller.
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.

Hello. My name is Tan.

Not likely you messed up the timing. There is no real adjustments unless something was left disconnected from the armature plate. If it idles ok and only misses at high speed it is more likely you have a failing ignition coil.

Do you have a timing light to test the spark when engine is messing up?

Customer: replied 1 year ago.
I do. Last time on the lake about a month ago it ran great, so I doubt it's one of the two coils.
Expert:  Tan replied 1 year ago.

It has to be an ignition issue as you only have one carb. So it will be either the power pack, sensor assembly or an ignition coil. Any one of these can fail without any signs. So why do you doubt it is one of the coils? Have you verified it is not one of the coils?

The symptoms are of a failing coil under a load.

Customer: replied 1 year ago.
I think I fixed it. What I thought was the idle speed adjustment actually adjusted the armature assembly, which I disassembled to remove the starter. I made the correct idle adjustment and then set the armature adjustment and now it runs at high speed just fine. I'll take it back to the lake tomorrow.
Expert:  Tan replied 1 year ago.

Ok keep me posted.

Customer: replied 1 year ago.
I'll know for tomorrow after a good run on the lake
Expert:  Tan replied 1 year ago.

OK great.