Topic: 1955 big twin – bottom plug fouling – Antique Outboard Motor Club,Inc

This topic has 15 replies, 5 voices, and was last updated 9 months, 2 weeks ago by fleetwin.

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July 16, 2023 at 1:07 pm #278108
The red boat
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US Member - 2 Years
I haven’t had a chance to run my 55 crestliner boat since last summer. It ran great last year and has been in dry storage. It has the 1955 evinrude 25hp outboard.

I took it out today and my bottom plug is getting fouled and it’s only running on 1 cylinder.
it starts and idles and operates at low speeds perfectly.

it has new plugs and wires and atom ignition modules. I’ve rebuilt the entire ignition system a couple of years ago.
like I said – it ran great the last time it was out.

what should I look for first?
July 16, 2023 at 1:26 pm #278111
The red boat
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US Member - 2 Years
Looking back on my previous posts I had the exact same issue in October 2020!

the resolution then was to swap out the atom module with a new one. I guess I’ll try that again but it seems odd that the one serving the bottom cylinder would fail again.
July 16, 2023 at 2:00 pm #278113
fleetwin
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US Member - 2 Years
It is possible that the plug just “fouled”, and perhaps a new plug will solve the issue.
July 16, 2023 at 2:05 pm #278114
The red boat
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US Member - 2 Years
I tried a couple of spare plugs while out on the water. All of them fouled almost immediately.

it will idle and run great as low as 500 rpm. Low speed is perfect and starts immediately.
July 16, 2023 at 2:52 pm #278115
crosbyman
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Canada Member - 2 Years
are you saying it fouls up only at higher speeds ? ?? or does it also foul up at idle after a certain period because if the pugre valse and/or passages are blocked excess fuel-oil will accumulate and cause fouling

Joining AOMCI has priviledges 🙂

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The red boat
July 16, 2023 at 3:33 pm #278120
bob-d
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Red Boat, I got fooled with my big twin once. Ran and idle beautifully. Couldn’t get it up to speed. Chased it thinking a fuel problem. Turned out to be a bad coil. It’s amazing how well big twins run and idle at slow speed on one cylinder. Go through the entire bottom spark plug circuit.

Bob D

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The red boat
July 16, 2023 at 3:35 pm #278121
The red boat
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US Member - 2 Years
I think it’s at all speeds.
Another clue I just remembered: I first started it in the tank yesterday and the cut-out switch worked as expected when I revved it. I didn’t rev it much because I was messing with the carb adjustment screws. But the longer I worked on it the less it wanted to rev and the cut-out just seemed different. I attributed it to an inability to rev due to a fouled plug.

I figured I should just get it on the water with a new spark plug and let it run. Looking back perhaps the cut-out was disabling my bottom cylinder?

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76-j
July 16, 2023 at 3:36 pm #278122
The red boat
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US Member - 2 Years
Bob-d: Sounds like my problem. I’ve tested the coil when I rebuilt the system but I can’t find the procedure here. Do you have a link??

edit- found the link.
Will test coil and rest of ignition system for the bottom cylinder on Friday and report back.

thanks for all the replies!
July 18, 2023 at 2:42 pm #278208
bob-d
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Red Boat, a super simple test for spark in the entire circuit is just take the plug out of the motor, insert back into connector, and ground on the powerhead. I use small flat round magnet from Home Depot to hold the plug against the powerhead. Gives a good connection, and is a super easy method. Make sure the lower unit is in a barrel / lake crank the motor, and check for spark.
You can change plugs very easily with this testing configuration to see if they are the problem. I hate to say I have never had good luck with Atom modules, but as they say …. individual result may vary. Don’t be afraid to swap coils, or go back to good old points and condensers. Check your boot connector on the top of the plug as well. I had a brand new coil from CDI once that was a dud. Electronics in todays boating world can be dicey. Not the same quality as before. Good luck, you will figure it out.
Bob D
July 19, 2023 at 9:41 am #278260
The red boat
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US Member - 2 Years
Thanks for the reply.

I have several pairs of spark plugs that have tested out ok. I tried swapping them around during my troubles but it didn’t make any difference – still no running on the bottom cylinder and immediately blackening/oily plug.

I have 2 new coils I just received in the mail. I will bench test them before using them. Before I install one for the lower cylinder I will do likewise with that coil mounted on the motor.

If all that checks out I may be going back to points and condensers (If I can remember where I stashed them).
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