75 9.9 running on only bottom cylinder

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meddybempster

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Jun 18, 2013
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I have good spark on both cylinders, good compression on both cylinders also but it only runs on the bottom cylinder. Top plug comes out damp, but not flooded with fuel. Any ideas anyone?
 
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slate1234

Petty Officer 1st Class
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Jul 1, 2012
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Re: 75 9.9 running on only bottom cylinder

Could be the wireing, have you tested coils ect, also year model number might help
 
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meddybempster

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Jun 18, 2013
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Re: 75 9.9 running on only bottom cylinder

slate1234 said:
Could be the wireing, have you tested coils ect, also year model number might help
Click to expand...

Its a 1975 Evinrude 9.9 hp with electric start (pull start also).
The model number is 10524C.
Both plugs have spark.
Compression was 100lbs on both cylinders.
Carburetor was removed, dismantled, cleaned and blown out with compressed air.
 
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basbalj288

Petty Officer 3rd Class
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Jul 17, 2009
Messages
88
Re: 75 9.9 running on only bottom cylinder

I had a very similar problem and diagnosis and yes had spark on both plugs but after trying everything I said the heck with it and just replaced the coils and hocus pocus it ran perfect again. So might give it a shot anyway. Cost about $30 a coil online.
 
RogersJetboat454

RogersJetboat454

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Re: 75 9.9 running on only bottom cylinder

How are you testing spark?

Making a spark plug spark in the open air is not a good measure of how well an ignition performs. Remember that spark plug has to fire in a pressurized combustion chamber with fuel.

If you don't have one, get a hold of a spark gap checker, sold in most auto parts stores.
Looks like this;
22983650_the_thx404_pri_detl.jpg

Ignition should be able to fire across at least a 7/16ths gap.

Have you pulled the flywheel at all to inspect the ignition? Your points may be dirty, misadjusted, or burnt out.
 
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