Johnson evinrude 50hp 2 cylinder Compression? Early 80s

[alangranton]

On the way back in from a north sea fishing trip the engine sounded rough under load.
It seemed under powered but not enough to worry me.

So tonight i did a compression test.
The results below.

top cylinder

bottom cylinder

The top chamber did not look like it was firing, no soot on the plug,it looked a little corroded.
The spark from the top coil is yellow not blue when the plug is held against the engine block and the engine turned over.

The engne will not start with the bottom ht lead disconnected. however the engine runs fine wiith the top ht lead disconnected.

1 is the compression ok?
2 should i think of changing the top coil?
3 any advice?

Many thanks
Alan

 

[boobie]

Re: Johnson evinrude 50hp 2 cylinder Compression? Early 80s

Swap the coils around and see what happens. Both coils should jump a 7/16" open air gap. The spark plug tells you nothing.

 

[jbjennings]

Re: Johnson evinrude 50hp 2 cylinder Compression? Early 80s

The compression has a suspicious amount of difference between cylinders, but is probably fine.
Your motor is not firing on the top cylinder. Switch coils between cylinders and see if the problem follows the coil. If so, replace coil and go boating. Don't buy a new coil until you check them as presented above, or you may waste your money.
If it's not the coil, you'll have to do an Ohm test on the stator.
As to the corrosion on the top plug and the suspicious amount of drop in compression on the top cylinder, I'd think long and hard about replacing the head gasket. Very easy to do, if you use the right tools. Be very careful NOT to break off the bolts. If you do don't even consider using an "EZ out". Just ask about how to remove them. You must use a torque wrench and preferably new head bolts to install the head. Lay the cylinder head on a pane of glass to check for warpage. If it is, put it on a piece of glass covered with 400grit sandpaper and flatten the head with a figure 8 pattern on the sandpaper.
Good luck,
JBJ

 

[alangranton]

Re: Johnson evinrude 50hp 2 cylinder Compression? Early 80s

am i right thinking this engine number is 1980 ?
J50BELCSS

 

[larryg]

Re: Johnson evinrude 50hp 2 cylinder Compression? Early 80s

you are right its a 1980.

 

[alangranton]

Re: Johnson evinrude 50hp 2 cylinder Compression? Early 80s

many thanks

 

[larryg]

Re: Johnson evinrude 50hp 2 cylinder Compression? Early 80s

when you check the johnson/evinrude model number take the 3rd n 2nd letter from last.such as yours cs.spell out introduces.i=1 n=2.up to e=9 s=0.(1-9 then zero).c=8 s=0 1980