OMC Saildrive losing power

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David20613

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Jan 22, 2008
5
Oday 28 Flowery Branch GA
My 1979 O'Day 28 has an OMC saildrive, model 15s10s, that is losing power when trying to give it any throttle. Both plugs foul up quickly indicating running too rich, or excess fuel getting into the combustion chamber, and they are wet each time I remove them. The carb and fuel pump have been rebuilt, and the oil recirculation lines replaced, with no improvement. It idles fine, but struggles when increasing the throttle under load. It goes into gear fine, the prop turns, and it is not fouled. Tried hotter plugs, same problem. Have been using non-ethanol 90 octane fuel with valv-tec added by the marina, plus I add one oz of Stabil per six gal. of gas.
Carb adjustments are by the book, and the advance is working.
I am out of ideas.
What do you think is the next step? Installing an outboard is not an option.

Help!

David
 
caguy

caguy

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Sep 22, 2006
4,004
Catalina, Luger C-27, Adventure 30 Marina del Rey
David20613 said:
Yes, the OMC Zepher model 15S10S
Click to expand
If you do decide to get rid of it let me know. Mine was under water for about a year and is toast. How is your saildrive? Most I've seen look like swiss cheese.
 
anchorclanker

anchorclanker

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May 27, 2012
1,152
Oday 222 Beaver Lake, Arkansas
Have you checked compression or crankcase pressure? Sounds like you need to start from scratch and trouble shoot it.
 
Squidd

Squidd

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Sep 26, 2011
890
AMF Alcort Paceship PY26 Washburn Wi. Apostle Islands
Have a mechanic do a leakdown test which will pinpoint a problem in the rings, valves or head gasket...

Next would be to check timing (shearedf flywheel key) and then...

Suspect failing coils at higher rpm...
 
caguy

caguy

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Sep 22, 2006
4,004
Catalina, Luger C-27, Adventure 30 Marina del Rey
If you would like I have the parts blow up diagrams for that motor and also the service manual. I was going to send you the link to where I got them from but that website has closed down. Send me you email and I will send them as an attachment.
 
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David20613

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Jan 22, 2008
5
Oday 28 Flowery Branch GA
Thanks for the offer to send the parts and service manuals. I have both. Thanks again.
 
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David20613

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Jan 22, 2008
5
Oday 28 Flowery Branch GA
Compression on each cylinder was around 115 to 120. How do you do a crankcase pressure test or a leakdown test on a two cycle?
 
D

David20613

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Jan 22, 2008
5
Oday 28 Flowery Branch GA
Boat is out of the water in the service yard, and the lower end really looks good. Replaced the lower end oil, and it was not contiminated by water. Zincs are fine. Boat has only been in fresh water.

FYI: If you are looking for a potentially re-buildable OMC saildrive, I looked at one here in Georgia that had been run hard and put away very wet (salt water), and was completely siezed up. Owner was looking for $800. Seemed like too big a risk for me.
I'll send you contact info if you are interested.
 
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