Topic: Can’t find the cause – Antique Outboard Motor Club,Inc

This topic has 10 replies, 9 voices, and was last updated 9 years, 2 months ago by count.

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July 16, 2015 at 4:28 pm #2029
count
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I went out with my ’62 fisherman a couple weeks ago. It ran excellent for about the first 4-5 miles of the journey. Then gradually started slowing down, losing rpm, over the period of about 10 minutes until it finally just stopped. Even squeezing the fuel hose bulb didn’t help. I held the throttle wide open the entire time hoping to make it back to the dock. I had to get towed back. I assumed it was a blown head gasket between the cylinders. We checked all sorts of stuff at the dock but found nothing wrong. We switched tanks and it fired right up and ran perfectly again. So we blamed the AVGAS that had in the first tank, and were satisfied that we had solved the problem.

Today I went out with my ’59 Fisherman. It ran like a scared rabbit for about the first 3 miles, then started slowing down. No AVGAS this time but same symptoms. I started pumping the bulb on the gas hose and it seemed to help a little. I made it back to the dock but the motor was not running at its usual speed. The only thing common with the first motor was the tank/hose.

Your thoughts??
July 16, 2015 at 4:53 pm #20240
mike-stroz
Participant
Are you sure it wasn’t overheating? I had the same symptoms with my Lightwin when the water pump failed, although I didn’t run it until it died. I tried it after it had cooled off and it ran fine.
July 16, 2015 at 6:38 pm #20247
frankr
Participant
US Member
So, have you ever looked at or replaced the ignition coils? Your symptoms are typical of cracked ones, and they ALL are cracked unless they have already been replaced.
July 16, 2015 at 6:40 pm #20248
Michael
Participant
International Member
Shockabsorber in lower unit. possibly too long causing it to bind up
July 16, 2015 at 7:11 pm #20249
fleetwin
Participant
US Member - 2 Years
Good point about the shock in the gearcase, I forgot about that.
Have you inspected/drained the gear lube?
July 16, 2015 at 7:30 pm #20253
jeff-register
Participant
US Member - 2 Years
Is it hard to pull over once it stops, Does it burn your finger. The guys above about covered it. Please follow & report back.
July 16, 2015 at 7:37 pm #20254
chinewalker
Participant
US Member
3 miles is a long way to go for the shock absorber to bind up. They usually either bind or they don’t.

Fuel tank commonality – what type of tank is it? How’s the vent on it? If it’s the standard old OMC single line tank with the tiny pins beside the lock and fuel pins, one or both of those might be plugged up or not functioning. One is a vent to let fuel in, the other is a valve to let fuel out.
July 16, 2015 at 8:26 pm #20257
fleetwin
Participant
US Member - 2 Years
another good thought about the vent. Usually the primer bulb would collapse when the vent is plugged, but it is sure easy enough to just loosen the fuel cap when the engine starts faltering. Or, perhaps switch fuel tanks when the engine starts to mess up.
July 16, 2015 at 9:35 pm #20262
The Boat House
Participant
- This reply was modified 5 years, 10 months ago by The Boat House.
- This reply was modified 3 years, 7 months ago by The Boat House.
July 16, 2015 at 10:45 pm #20265
jerryswiss
Participant
As others have stated, check the tank vent. Try the same tank and one of your motors again and if the motor starts slowing down, unscrew the tank cap. If it helps, that is your problem 🙂

P.S. also check for a partially clogged fuel line especially around the engine connection.
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