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Johnson CD-12 final inches problems

M

MartinZ

Member
I have a CD-12 that I am working on and have a few problems to figure out. One of them that I think is serious is the way the spark advance mechanism shakes rapidly back and forth at low throttle. I took the flywheel off and smoothed out the edges with some sand paper in case maybe it was catching on some burs, but that might not be what's causing it. It didn't fix it anyway.

This is a short video of what it is doing. I'll try to lower the throttle to fine tune the low speed jet, but then it starts this shaking and dies.


The low and high speed jets both seem a little loose, like they can both wobble a little, and I don't they are supposed to. I might see if I have some more of the packing rings left over and get them tightened up. If they are able to suck air, could that be what is making the spark advance wobble at low throttle?

Another issue I need to solve is the leaking pressure tank. I think I'm just going to convert it to normal fuel pump. I rebuilt the entire tank and it still leaks like crazy if there's any pressure in it, even from sunlight induced heat expansion. Right now I have an old mower tank on a shelf up high gravity feeding while the motor is in a drum.

The engine got hot enough to boil water in just a minute of running it, so I don't think it's circulating water anymore. I'm pretty sure it was in the past, because it never got boiling hot like this before and I've had it out on the lake. As far as I know, there's no tell-tale, so I'll have to investigate.

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Yep, that'll do it.

Didn't realize you have to remove the powerhead to get the lower unit off. Guess I'm in for some new seals and gaskets now.
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I got the coils adjusted so they aren't rubbing anymore, and the spark advance doesn't jump around like it did. I got the impeller replaced and with a few new seals, it now has good visible water flow. I spent hours playing with the jets, trying to get it to idle down without dying. I adjusted the idle advance setting and that made it better. I pulled the carb and gave it a cleanout and that made it even better. It's not perfect, but I can idle it down pretty low and shift it into gear without it dying. I still need to check/change the lower gear oil.

Other than that, it's ready to go back out on the water and maybe it won't leave me stranded this time.

 
It has a bad skip/miss when on the water that doesn't really show up in a barrel.
It tops out at 6 mph on my 10ft flat bottom. The same boat does 5 with a 2.6hp and 8 with a 4hp.

I'm doing coils, points, and condensers. Waiting on parts. Both the coils have big giant cracks, so they are probably not performing at 100%.
 
Replaced the coils, points, and condensers. Still misses. Actually worse than before.

Pulled the plugs and noticed water on the bottom plug.

Spun the engine with a drill with both plugs out. Water gushing out of bottom cylinder.

I think I'm about done with this one.
 
With only the top plug in use, bottom plug removed, the engine will run, but very very badly. With both plugs in it will run wide open, but no idle, and only in neutral.

In a lake, it will push a 10 foot jon boat 6mph, with one cylinder half full of water, lol. This is why the fuel mix has been such a chore.

It's impressive though.
 
I checked in the box of parts I have for this motor, and found the original head gasket. So this motor did have a new one, but I can see the little grooves where it blew out. Hopefully that is the source of the water ingress. I will order a new gasket.

I might have also used a dab of RTV to test my theory, and the cylinder is no longer gushing water.
 
35 and 40 psi on the compression test. New head gasket hasn't come in yet, but I don't expect it to bring the compression up to 70 or 80.
 
You might be surprised on this one.----The head is warped.-----They all are !-----Resurface it with emery on a piece of glass.
 
Got another gauge. 85 and 90. Compression is fine.

Waiting on some solid core spark plug wires and then after some new plugs, that's the entire spark system replaced.

If not weak spark, fuel. I have it converted to vacuum fuel pump. When I run it in the barrel, I have the tank on a shelf 6 feet off the ground. It runs wide open throttle like that, but not in gear, because it's in a barrel.

On the lake the tank is about 12 inches below the engine, on the bottom of the boat. It will still throttle up like that, in neutral. Doesn't have any guts when you put it in gear, though. I even used my other boat to pull the test boat and see if the engine would throttle all the way up while in gear if another engine was taking the load, and it wouldn't do it. I was in one boat, wife in the other. Maybe that points to being fuel starved.
 
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