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Red X Angler
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16,054 Posts
Discussion Starter · #1 ·
Ok, I have hit a stump. I have a 1979 Evinrude 55hp 2 cyl. I have rebuilt the carbs, replaced the fuel pump, coils, power pack, plugs, wires, wiring harness. I have double checked my rebuild, replaced the fuel lines and vacuum line. Line and bulb from tank, cleaned the tank, tried a new tank, synchronized the carbs, replaced the choke return spring. Checked the compression 130psi each.
It runs good on the hose, idles decent but this model has the "fixed" air adjustments so you cant fine tune the idle. Accelerates good on the hose both plugs firing and burning equal.
Put it in the water, cranks and idles ok, push it in gear and it will not rev up. Cant get the rpms all the way up and feels like one cylinder comes in and out like it's starving but its not. I can pump the bulb , no difference, I can shoot cleaner in the carbs while accelerating on the water, no help, just bogs more. Carb drains are full when I check the bowls so its getting gas. High speed circuits are clean, low speed jets are clean. Timing checks out. Timing advance is working.. I am at a loss here..
 

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Red X Angler
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16,054 Posts
Discussion Starter · #3 ·
all the electrics are solid, I have even monitored the cylinders with a spark indicator under load.
Sounds mighty electrical to me dude. Let me give it some thought and do some research...
 

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Red X Angler
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16,054 Posts
Discussion Starter · #5 ·
I think the cutting out may be more of an issue of it loading up because the engine isn't accelerating. I can knock it in neutral and rev it and it cleans right up. Hold it at high rpm in neutral and it fluctuates but doesnt skip. I even tried a different set of new plugs and the old wires just seeing if it might be a plug or wire breaking down from the factory.
 

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Red X Angler
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16,054 Posts
Discussion Starter · #7 ·
93 octane with Seafoam ethanol free. It can idle and warm up for 20min and still no difference, pee water is warm in a few minutes, so it's heating like it should.
 

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If you think it is fuel related I would be very careful running it. Don't want to burn up that cylinder dropping out.

I would run it and try to isolate which cylinder is dropping. Reverse plug wires and see if it is the same cylinder.

Not trying to talk down to you in anyway. You know what you are doing but sometimes frustration can help us over look things.
 

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Red X Angler
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16,054 Posts
Discussion Starter · #11 ·
no excessive compression leakdown, cylinders are balanced. Voltage stays constant to both coils during run and with engine off, key on, while moving wires around so no breaks or shorts I can find. Strong spark across spark tester even under load. I am going to look over the timing advance again..
 

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Red X Angler
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16,054 Posts
Discussion Starter · #12 ·
After I run it on the river or on the hose I read both plugs, coloration is the same on both, both burning reasonably clean. No oil build up or anything to make me think one isn't burning off as it should.
 

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Red X Angler
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16,054 Posts
Discussion Starter · #13 ·
Reed valves all feel tight and spring like they should when I spin the engine with the carbs off. Sprayed cleaner around all the gaskets with engine running and go no change in speed so I don't think I have any vacuum leaks on bases or reed plate.
 

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Red X Angler
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16,054 Posts
Discussion Starter · #17 ·
I just checked the timing again and resynced the carbs. Top cylinder wasn't pulling quite the vacuum, and it seemed to be helping then I had a serious problem. Don't know how many of you are familiar with an engine "running away" but mine just did. cut off the switch, snatched off the plug wires and it just kept screaming higher and higher. closed the choke and it took off for the moon fire shooting out of the prop exhaust, I snatched off my shirt and shoved it into the carbs and got it to stop. Overheat alarm was screaming. This is caused by either carbon buildup making a hot spot on a piston or a serious overheating of one or more cylinders. It causes the incoming fuel to burn just like a spark plug firing.
I have to go to class so cant work on it anymore today but not feeling good about it I have to admit. I'm going to check compression again after this mishap and if its good , I will pull the flywheel and look the electronics over. I sure wish I was putting this time and $$ into a bigger engine but no turning back now.
 
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All to familiar with engine run away, but a jet engine not an outboard. One of the big things that will cause run away on a jet engine is low voltage input.

A carbon build up is very likely in your case. It may not have caused the issue but it's there now and needs to be dealt with. I would get a can of Power Tuner and run it through the motor for a full decarb
 

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Have you double checked the LEVEL of the carb. floats. I know I have chased a similar problem and did not have the floats level. One other thing is the stator in good shape? When a stator get warm / hot all sorts of funny things can happen.
 
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