High speed misfire on 1955 10 seahorse Johnson

[muskokadean]

I have a 1955 10 seahorse Johnson that is misfiring on the bottom cylinder at high speed. I had the motor rebuilt awhile ago and had every thing replaced wires plugs magnetos. I took out this weekend for the first time to see how it ran. New gas and oil missed at 24:1.I tried changing the plugs around but to bottom cylinder plug keeps coming out fowled up. At high speed- 3/4 to full there is a mis in the engine almost every 3 seconds. It misses so bad the whole engine shakes like you have hit a rock. Any one have any idea on what would cause this?

 

[HighTrim]

Re: High speed misfire on 1955 10 seahorse Johnson

Does it sound like an ignition pop, or more of a lean sneeze? Try richening the hs needle, does it go away?

 

[nwcove]

Re: High speed misfire on 1955 10 seahorse Johnson

you may have a couple of issues going on. dirty points on the bottom cyl ? the next issue could be as simple as a lean sneeze, or more likely, from your description of " hitting a rock", you have a bad clutch dog. what was the extent of the rebuild?

 

[muskokadean]

Re: High speed misfire on 1955 10 seahorse Johnson

you may have a couple of issues going on. dirty points on the bottom cyl ? the next issue could be as simple as a lean sneeze, or more likely, from your description of " hitting a rock", you have a bad clutch dog. what was the extent of the rebuild?

When the motor was rebuilt the lower end gears and bearing was replaced, the shift handle and rod was replaced. Points and magneto, wires, & plugs replaced. Carb rebuilt all new gaskets, needle jets, float and packing. What is weird is you can set your watch and it seem to happen at 3 second intervals. Can you tell what you mean by a lean sneeze? Thanks for the reply.

 

[muskokadean]

Re: High speed misfire on 1955 10 seahorse Johnson

Does it sound like an ignition pop, or more of a lean sneeze? Try richening the hs needle, does it go away?

Just a loud bang. will try and change the lean setting

 

[HighTrim]

Re: High speed misfire on 1955 10 seahorse Johnson

By your name, are you in Ontario?

Sounds like your clutch dog then as noted by nwcove. Especially since it happens at high speed.

 

[muskokadean]

Re: High speed misfire on 1955 10 seahorse Johnson

Yes we are in the Bracebridge area. What is the clutch dog and how do I find and fix that?

 

[HighTrim]

Re: High speed misfire on 1955 10 seahorse Johnson

Nice area, I boat just south of you in Gravenhurst.

The clutch dog sits between the forward and reverse gears. It has lobes, or ears, that are precisely machined that engage the gear when shifted into either forward or reverse. Now, when these lobes get worn, due to improper shifting, or improper shift linkage setup, the motor will slip out of gear as the RPMS increase, then get thrown back into gear by the shift linkage, causing the bang you hear. Sort of sounds like you hit an underwater log. Classic symptoms of a worn clutch dog.

To remove, inspect, invert the motor, then take out the standard screws holding the skeg onto the gearcase. Pull out the prop shaft, and swap the dog, then reinstall in reverse order. You will need a new spaghetti seal, and some 3M 847 to do the job.

 

[HighTrim]

Re: High speed misfire on 1955 10 seahorse Johnson

#32 here, part number 375711

Vintage Evinrude Johnson Outboard Parts & Diagrams - Catalog 376367

Evinrude Johnson OMC 375711 - Clutch Dog @ MarineEngine.com

Dont pay that price though, lol. That is just to show you the part and part number.

 

[muskokadean]

Re: High speed misfire on 1955 10 seahorse Johnson

#32 here, part number 375711

http://www.marineengine.com/parts/vintage-evinrude-johnson/376367/37636700001.htm]Vintage Evinrude Johnson Outboard Parts & Diagrams - Catalog 376367[/url]

Evinrude Johnson OMC 375711 - Clutch Dog @ MarineEngine.com

Dont pay that price though, lol. That is just to show you the part and part number.

Thank you very much for the help. Where would the best place be to order the part?

 

[kfa4303]

Re: High speed misfire on 1955 10 seahorse Johnson

Hi musk. You can find parts on ebay, marineengine.com, and the classifieds of aomci.org. I've had great success at aomci.org myself. You'll just have to shop around to find the best deal. This link may help too.

Johnson

 

[HighTrim]

Re: High speed misfire on 1955 10 seahorse Johnson

A local AOMCI member will be the cheapest usually. If you get stuck PM me, I normally dont like selling them as Im a hoarder, lol

 

[HighTrim]

Re: High speed misfire on 1955 10 seahorse Johnson

This one does not look too bad. Looks like he wants to make his money on the shipping though!

375711 OMC 0375711 "Vintage" Clutch DOG 9 5 20HP 1950'S AND Later Model Years | eBay

 

[nwcove]

Re: High speed misfire on 1955 10 seahorse Johnson

wow! the shipping cost on that dog is a bit out there. ( i had a long block powerhead shipped across the border for $90, if i remember correctly, it weighed 18 lbs )

 

[muskokadean]

Re: High speed misfire on 1955 10 seahorse Johnson

Yes I seen this one I am trying to give the guy a call to see if he can ship reg mail

 

[muskokadean]

Re: High speed misfire on 1955 10 seahorse Johnson

Yes I seen this one I am trying to give the guy a call to see if he can ship reg mail

 

[HighTrim]

Re: High speed misfire on 1955 10 seahorse Johnson

What alot of sellers do now is make the price cheap, then hammer the shipping to try and make money that way. Just a sales tactic, alot wont lower their shipping as they want to get their money out of it one way or another.

 

[cgodfrey]

Re: High speed misfire on 1955 10 seahorse Johnson

Not to hijack this topic, but to combat this, eBay's been including shipping charges in their final value fee calculations for a few years now. It irked the sellers who weren't skirting ebay fees by overcharging on shipping, but eBay doesn't like being cheated either...