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#11404008 - 02/09/16 07:14 PM Antique Johnson 5.5 Question
IslandJim Online   content

Registered: 07/08/14
Posts: 156
Loc: Rockport, TX
I have a 1961 Johnson 5-1/2 Twin outboard that I have worked on, putting a new impeller in, new lower unit seals, and it runs O.K. in my driveway. When I take the boat out, it only runs on both cylinders when it is at wide open throttle. If I back the throttle off any amount, the top cylinder doesn't fire. In my driveway, if I pull the plugs and ground them to the case, both plugs fire fine. I don't have a compression gauge, but the workglove-in-the-sparkplug hole test shows approximately equal compression. Does this sound like an electrical problem? I sanded the points with 1500 grit sandpaper. Maybe I need to dump the points and condensers and install electronic ignition modules? Anyone done this?
It's really hard to come into a ramp dock at W.O.T.

Thanks, Island Jim
I'm an Eighth Day Adventist. On the Eighth Day, God went fishing!

#11404034 - 02/09/16 07:27 PM Re: Antique Johnson 5.5 Question [Re: IslandJim]
Cat finder Offline

Registered: 03/14/15
Posts: 273
Loc: Dallas, Texas
A compression check is in order.could be caused by excessive blow by pass the piston rings. If so you might be able to free them up if they are stuck with a little sea foam deepcreep.
If the fish don't bite your not baiting right...

#11404297 - 02/09/16 08:59 PM Re: Antique Johnson 5.5 Question [Re: Cat finder]
hicr_nut Offline
Green Horn

Registered: 11/07/09
Posts: 3
Loc: Joaquin, Texas
Head gasket blown between the two cylinders.

#11404619 - 02/10/16 02:23 AM Re: Antique Johnson 5.5 Question [Re: IslandJim]
boatwhisperer Offline
Extreme Angler

Registered: 09/25/10
Posts: 1476
Loc: hurst, tx
check the point gap on the set of points for number 1 cylinder and check the armature play brass bushing it is probably wore out

#11405764 - 02/10/16 02:45 PM Re: Antique Johnson 5.5 Question [Re: IslandJim]
IslandJim Online   content

Registered: 07/08/14
Posts: 156
Loc: Rockport, TX
Thanks for the suggestions, guys. I ran it in my driveway for a long time this morning. It was pumping water fine, and ran and ran in reverse, and hit on both cylinders. I took the boat to the ramp and unloaded it and it ran only on one cylinder again. I got away from the ramp, and turned the throttle wide open and after a bit, the second cylinder kicked in and it ran like crazy. If I back the throttle off any at all, it returns to one-lunging. I'm wondering if something is wacky with one of the reed valves? The engine sat for ten years, before I got it and started trying to resurrect it.

When it is running on both cylinders, it's strong and the 12-foot skiff I have it on planes easily. Because of that, I don't think a head gasket is blown, or the rings have a problem. I adjusted the points that were wide, and the plug gaps that were also wide, but those changes did nothing to alleviate the one-lunging at other than full wide open throttle. Any other ideas?

I used to build 2000 horsepower blown nitro Chryslers, but this 5.5 two-stroke has me baffled. I know that God didn't intend for engines to run with out intake and exhaust valves!

Thanks again, Island Jim

#11410815 - 02/12/16 07:13 PM Re: Antique Johnson 5.5 Question [Re: IslandJim]
IslandJim Online   content

Registered: 07/08/14
Posts: 156
Loc: Rockport, TX
For those who might care, my whole problem was just an old, cracked spark plug wire. It was arcing to ground on the timing plate. When I went to wide open throttle, the plug wires were pulled tight and it couldn't arc to ground, so it ran on both cylinders. As per usual, most problems are caused by small, simple things that are hard to isolate. I could have thrown lots of $25 parts at this, but I can fix it with $3.00 in plug wires!



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