1996 25hp Yamaha Compression

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bayscallop

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Oct 20, 2011
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Hi, hopefully someone out there can help. I have a 1996 25HP Yamaha pull start engine. The engine starts great, idles nice, and runs very strong. I just did a compression check on it today for the heck of it and it tested at 60 psi in both cylinders. I removed both plugs and pull the cord two or three times for each check. I even borrowed a different pressure gauge from my neighbor and it came up the same. Am I doing something wrong or can an engine run great w/ 60 psi per cylinder. I was always under the impression it should be about 115 -120. Any ideas?????
 
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99yam40

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Sep 7, 2008
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8,878
Re: 1996 25hp Yamaha Compression

Did you open the throttle some so it could get some air to compress?
I would have expected more also.
It is also a good idea to short to ground the plug wires or pull the kill switch to eliminate the spark while turning over
 
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robert graham

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Re: 1996 25hp Yamaha Compression

bayscallop said:
Hi, hopefully someone out there can help. I have a 1996 25HP Yamaha pull start engine. The engine starts great, idles nice, and runs very strong. I just did a compression check on it today for the heck of it and it tested at 60 psi in both cylinders. I removed both plugs and pull the cord two or three times for each check. I even borrowed a different pressure gauge from my neighbor and it came up the same. Am I doing something wrong or can an engine run great w/ 60 psi per cylinder. I was always under the impression it should be about 115 -120. Any ideas?????
Click to expand...
If it "starts great, idles nice and runs strong", why even worry about it?...there's apparently nothing wrong with the motor...go fishing and be happy!;)
 
JB

JB

Honorary Moderator Emeritus
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Messages
45,907
Re: 1996 25hp Yamaha Compression

60-60 is excellent for a pull start outboard. Any psi spec is fantasy.

Throttle position is irrelevant.

You usually need 5 or more pulls to get consistent readings.

Of course, if you are really desperate to find something wrong send it to me. I will part it out if it ever quits. :p
 
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bayscallop

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Re: 1996 25hp Yamaha Compression

Thank you for the input. I got in touch with a Yamaha dealer today and he said as long as compression is about the same, don't worry about a thing. He stated not all engines were desined to have that 100+ compression. Thank you again for the responses.
 
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