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I have a 15' 1974 Seaswirl tri-hull with a 1975 Johnson 70ESL74 motor. We are the third owners and it has been in the family since new.
In the past this boat did everything including towing a skier with 3 people in the boat. It would get up to about 37mph without the skier.
It sat for about 10 years and was only ran once about 8 years ago. At that point it had full power but developed a issue with the coils. Father in law had them replaced and then it just sat until this year.
Runs fine, but has lost power since it sat. Compression is 98-100 in all 3 cylinders. Mixed info on line about whats right, but one source said 100lbs is correct. I would think if compression were the problem it would not be even on all 3.
I replaced the plugs and removed and cleaned the carbs as best I could and changed the lower unit oil. This helped a little but it still wont pass 30mph with 2 adults and a child. With this load it also takes about 20-30 seconds to get out of the water and plane. With 4 adults it simply wont do it.
Fuel filter screen is clean and all throttle linkages are in correct time. I have no tach so I cant tell you what RPM I get, but it seems low.
As best I can determine it has a 13.25 dia x 16.75 pitch prop, and this is the same prop it has had for a long time. It has also had a whole can of seafoam run through it over several tanks.
Suggestions as to why it runs weak? Things to look for? I don't have a book on this motor. If the motor is just tired (from sitting?) could going to a 15 pitch prop help it? Seems logical, would get the rpm's up again and should get on plane faster. Help!!
In the past this boat did everything including towing a skier with 3 people in the boat. It would get up to about 37mph without the skier.
It sat for about 10 years and was only ran once about 8 years ago. At that point it had full power but developed a issue with the coils. Father in law had them replaced and then it just sat until this year.
Runs fine, but has lost power since it sat. Compression is 98-100 in all 3 cylinders. Mixed info on line about whats right, but one source said 100lbs is correct. I would think if compression were the problem it would not be even on all 3.
I replaced the plugs and removed and cleaned the carbs as best I could and changed the lower unit oil. This helped a little but it still wont pass 30mph with 2 adults and a child. With this load it also takes about 20-30 seconds to get out of the water and plane. With 4 adults it simply wont do it.
Fuel filter screen is clean and all throttle linkages are in correct time. I have no tach so I cant tell you what RPM I get, but it seems low.
As best I can determine it has a 13.25 dia x 16.75 pitch prop, and this is the same prop it has had for a long time. It has also had a whole can of seafoam run through it over several tanks.
Suggestions as to why it runs weak? Things to look for? I don't have a book on this motor. If the motor is just tired (from sitting?) could going to a 15 pitch prop help it? Seems logical, would get the rpm's up again and should get on plane faster. Help!!