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compresion 1979

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boatbickle

Contributing Member
110, 110,110,90, 1979 evinrude. motor runs good. should I be worried about the compresion in the low cylinder? 17' 5'' duracraft boat. runs around 44 with just me in it. Is that a good speed? I am new to boating and dont want the motor to blow up due to bad cylinder.
 
Re: compresion

How long has that engine been sitting? If that last number doesn't come up soon it will surely be going down. I was in a similar situation a couple of years ago. I refurbed a 1973 3 cyl. (boat sat unused for 13 years) Comp was 100/100/80. Once I got it running and retested it was 100/105/100.
 
Re: compresion

yes decarb with seafoam. took it out today and it ran 45 on gps. strong motor. I havent checked the compresion yet. is 45 a good speed for this motor? I have a 21 pitch prop and a hydro foil. thank you
 
Re: compresion

Speed depends on how much the boat weighs, the prop, how its loaded, hull design, etc. However, 45 for a 17-18' doesn't sound too shabby if your engine is a 100HP or below. (HP is also a big factor, didn't see it listed.)
 
Re: compresion

You might get lucky,The ring could be possibly compressed in piston,Run some ring free through it ,maybe it will loosen it up if it is stuck.After that Try running a can of marine engine tune threw it,to get carbon blown out.Make sure you have it in the water not muffs on ,So you can run it wide open after doing the treatment to get all excess carbon out.Worth a shoot if your going to run till it blows.Good Luck
 
Re: compresion

It blew up. Had it wide open on lake hartwell sc. It just stopped running, got it started again but it was running bad and coughing and sounded like crap. pulled it into a cove and took the spark plug out of the low compresion cylinder and the spark plug was melted and looked like it got hit with a hammer. the boat now is listed on craigslist in the atlanta area. It was fun while it lasted.
 
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