help with 1980 Johnson 35HP

[Jay Ainslie]

Need help, i'm out of ideas...
I have a 1980 Johnson 35hp 2 stroke that is working only on the top cylinder. Both cylinders have excellent spark at the spark plugs. Compression is about 85 on both cylinders. Motor starts right up and when I pull the plug wire off the bottom cylinder, there is no change. I did a spark test with motor running on the bottom and spark is bright and at almost 1/2". I am now suspecting the fuel pump because I took off carburetor and removed and checked the reed valves. They were seating good...
Bottom spark plug is wet when I check it; actually the top one is also wet but not as much, because it is firing.
Could the low compression be the problem?
I am thinking that the fuel pump may be leaking fuel into the bottom cylinder? Any help would be greatly appreciated... I am out of ideas!
Thanks

 

[oldcatamount]

Re: help with 1980 Johnson 35HP

When you say the bottom plug is wet, is it wet with fuel or wet with water? I suspect a bad head gasket is the likely problem. A leaking head gasket can allow water into one or both cylinders and extinguish the spark. A bad head gasket may also be the reason for the low compression numbers.

 

[Jay Ainslie]

Re: help with 1980 Johnson 35HP

hmmmm I will check for water vs gas... About the compression: if I take both spark plugs out, install the compression gauge/tester and use the pull start to turn the engine over, the compression is at 85 on both cylinders. If I start the engine, (only the top cylinder is working), the compression on the lower cylinder jumps to about 100. I am confused as to why it would be higher with engine running vs me turning the engine over with the pull start..

 

[oldcatamount]

Re: help with 1980 Johnson 35HP

Has to do with rpm speed. The faster the motor is running, the higher the comp. numbers, but, a head gasket can leak water and not necessarily lose much compression.

 

[bonzoscott]

Re: help with 1980 Johnson 35HP

Both cylinders have excellent spark at the spark plugs. Compression is about 85 on both cylinders. Motor starts right up and when I pull the plug wire off the bottom cylinder, there is no change. I did a spark test with motor running on the bottom and spark is bright and at almost 1/2".

Did you pull the top plug wire while bottom was connected and try? What is the symptom while running the boat? Could be the fuel pump if you're saying will not run at low speed.

 

[Jay Ainslie]

Re: help with 1980 Johnson 35HP

Gentlemen, Thanks tons for the tip on the 'blown head gasket'. I pulled the head off and low and behold there was this creamy like liquid in the bottom cylinder (water mixed with gasoline/oil). I cleaned, and installed a new head gasket and the engine runs GREAT! I really appreciate all who posted possible solutions to my problem.. Happy Boating... !!! Jay