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Fouling 1 plug

Jerryjerry05

Jerryjerry05

Outstanding Contributor
About a 1982 50hp. 4 cy. Ser#5951619
Has good comp on all 4 about 150-155
Good spark on all 4
I can change the plugs around and the carbon stays on #3 cyl.
The reeds are ok.
The carbs spotless.
The fuel pump diaphragms both OK.

Starts and runs poorly.
The 3rd cyl. from the top carbons up real bad after a couple of min running.

The air screws are real hard to get anywhere close????
I don't see any blow back through the carbs.

Is it possible something in the exhaust chest has let loose?

Thanks,J
 
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-----------Cylinder compression is good.------------Spark is good----Carburetors are clean.--------------Well that leaves that other big mystery which is crankcase compression.---------------------Your best bet is to look into that aspect of 2 stroke operation.
 
How do I go about that??

The problem is the 3rd cyl and I'm thinking the bypass or transfer port might be blocked??

I know how to pressure test an automotive engine but an outboard has the exhaust open and impossible to seal.
 
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The problem is the 3rd cyl and I'm thinking the bypass or transfer port might be blocked??
Click to expand...
If it was restricted it would show lean, if you have build up of carbon/wetness its either overfueling or not burning the fuel its getting. If in my shop I would: (1) pull lower unit and check for exhaust blockage from carbon build up (2)DVA the voltage on that coil input (3) index the flywheel and check timing and keyway. Another thing to check that causes a crappy idle and hard to adjust is reed block locating bolt loose or missing(pulled hair on this for a week) but don't think it would cause carbon build up.
 
No flywheel key.
Racerone: Exhaust tuner?
Looking at the parts diagrams and don't find???

The owner decided he wants me to look into it.

Will let you know of any findings.
 
The flywheel comes off by removing 8 bolts/screws.
Then lifts off.
I'll take it apart and try to post pics.
It's indexed by the screw holes?????
 
??????---------No,----------The flex plate comes off and leaves the flywheel hub still on the crankshaft.-------------You do not remove those 8 bolts to remove the flywheel.-----------You remove the nut and screw a puller into the flywheel to remove the assembly.------Then you will find the key.
 
No, remove the bolts and the flywheel comes off.
This is the flywheel with the magnets built in not glued.
I've had it off 3 times.
The stator went bad and needed to be replaced.
The hub stays in place and doesn't need to be removed for what I did.
 
Your right but you don't need to pull the hub to remove the stator.

Maybe you just never removed the bolts?

I know I didn't remove the hub to replace the stator.
That's why I said "no key"

So actually we're both correct.
 
yzf125, what's he trying to say??

Kim. The spark like I said was good.
And I have 3 different spark testers.
Been doing this for over 30 years and have all kinds of tools.

The problem turns out to be a cracked cylinder wall.

I'm not a rookie who doesn't know how to diagnose a problem.
I tried everything I know and put it out there for others to see if they might have come across some problem that would cause this problem.

And on 3 different forums not one person said: hey it's a cracked cylinder wall!!
Kinda hard to tell even when it was completely torn down.

I was standing there scratching my butt and just happened to see a VERRRRRY tiny silver line on the side of #3(at first I thought it a scratch)
Pulled the pistons and cleaned the bore and found the inside with a network of cracks.

So problem SOLVED!!!

I'd like to THANK everyone who contributed to this thread.

I think the owners "buddy who knows everything" changed the impeller and gear oil.
The water tube grommet that fits in the top of the pump was gone/missing.
I think they used the boat and ran it hard?? and it got hot and the alarm didn't go off.
Got so hot that when they slowed down it blew cold water up in the cooling passages around the cylinders and the cracks appeared????
That's just a guess or the 1982 just decided to die??

Like I said thanks again.
 
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