How to troubleshoot water in cylinder & lowered comp (or should I bother)?

[Good Trout To You Sir]

Have had an awakened '69 4HP Lightwin on the water a handful of times. Not original owner. I replaced impeller and used carb kit. Cleaned points and gapped to 0.02. Ran pretty well a handful of times, but have been cautious on potential of overheating issue. Very old exhaust cover and head gaskets, but have been running motor with them.
Noticed motor becoming increasingly difficult to start. Many, MANY pulls in some cases.....or it had to "rest" and then would restart after lots of pulls. Have noticed a low "deflating" sound with slight fluttering after lots of pulls ---- pressure escaping from somewhere. Last trip motor slowed, stopped and then refused to restart. On stand, at least one cylinder will fire a few rounds, but motor refuses to run.
Removed plugs and noticed milky-oil-like residue on terminal of lower cylinder plug. Cold compression using loaner gauge has fallen from roughly 90 psi to just above 60 psi in both cylinders. Is it worth replacing exhaust and head gaskets to determine if they are at issue, or do symptoms likely describe motor death from some other cause?

 

[racerone]

Does spark jump a gap of 5/16" on a test device ?-----Sparkplugs are not used when doing this peak voltage / magneto output test !

 

[Good Trout To You Sir]

Although I cannot immediately answer that question, I can tell you that I increased the gap on the ancient J4C plugs to 0.035" and the motor seemed to fire just fine. Since you asked re: spark, I am assuming a link to water making its way into lower cylinder and to the decline in compression from 90=>60, but I'm not following.

 

[racerone]

Pull cylinder head and replace gasket.-----Reduce plug gap to 0.025" and see if it starts easier.

 

[Good Trout To You Sir]

Pull cylinder head and replace gasket.-----Reduce plug gap to 0.025" and see if it starts easier.

Will do-- if compression readings do not improve, should I expect this motor to run at balanced compression of 60 psi?

 

[Crosbyman]

I would just run it with a decarb product or engine cleaner

PSI might pick up some and you'll have a good troller .

 

[racerone]

Mere pennies for a head gasket.----Will allow you to see condition of cylinders.----Priceless information !!

 

[Good Trout To You Sir]

Understood. If folks have credible online resources in mind to which you can point the uninitiated on head & exhaust gasket install, efficient way to clean water passages and what to look for in cylinders, please do speak up.
The old engine service manual site (offshore) isn't loading for me and I would imagine there are do's and don'ts to get the best results. (Yes, I have the original '69 service manual. No, it's not helpful. Besides, materials & recommended procedures do change over time!)
Along with my $7 head gasket sourced locally, I picked up a loaner borescope from auto parts store. Have tools --- now all I need is knowledge for what I'm doing!

 

[Sea Rider]

Will do-- if compression readings do not improve, should I expect this motor to run at balanced compression of 60 psi?

Was the compression test done with motor cold or hot. A motor with very low compression ratio will be Hard to Start and that's normal. If a new head gasket doesn't work, there you have it. What's the factory PSI rated for when out of the box, probably 60 PSI is very low.

If it's a 2 stroke motor has it ever been decarbonized with Engine Tune Up , CRC Decarbonizer Sprays, not Sea Foam or any other type you pour in the fuel tank ? These guys do wonders most times...

Happy Boating​

 

[Crosbyman]

agree on post 7... changing the head gasket is not a big complicated job but it can become a nightmare venture if you snap headbolts .

it involves simple unscrewing of the head bolts , removing (scrappingT the gasket away , cleaning the cyl. head surfaces (recommended.... polish it evenly by doing circle 8s on 80-100 grit paper over a flat glass or ceramic tile for flatness)

reinstall the new gasket torque it down to specs test compression#s

retorque after a few hours of run time

lots of info available on the net
Maintaining Johnson/Evinrude 4h (leeroysramblings.com)
OMC 9.9 - 15hp (leeroysramblings.com)