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Old 03 September 2015, 17:21   #41
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If it's a chap in need of some mozzy spray I think we've been looking at the same youtube clip
If one cylinder was very low - as his was - I'd be repeating the test after putting some oil into the cylinder. If the reading then went up I'd suspect rings/bore/piston damage.
I've also been looking for a service manual for yours online, lots of owners manual that just give compression ratio free to download but the service manuals generally are on pay-to-download sites - - although I've just checked the service manual for mine & it makes no mention of compression test results.

If your plugs were older a steam cleaned look is a giveaway that a cylinder has had water into it.
Difficult to know which way to go, but in the absence of any other suggestions - or the problem having gone away after what you've done so far - I think the next step could be to remove the head & examine the bores & the state of the gaskets.
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Old 03 September 2015, 18:51   #42
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Ron

Search on here for outboard service manuals there are some free downloads.or go on eBay I got one for around 6 for a Suzuki 90 on d Isco, from what I have seen on a Yam50hp 125psi is the lowest recommended by Yamaha seen on YouTube getting 150psi
your within the recommended 10%between cylinders see if you can borrow another gauge as a comparison

Cheers

thanks found it, I download the large Yamaha/mariner file and found the figures at last... Section 6-147

Minimum compression =175.4
My gauge isn't decimal place accurate but the needle was on the good side of 175 so looks like it's all ok :-)
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Old 03 September 2015, 19:01   #43
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If it's a chap in need of some mozzy spray I think we've been looking at the same youtube clip
I think the next step could be to remove the head & examine the bores & the state of the gaskets.

Was there Mosquitos or does he have some kind of nervous tick 😂

I'm starting to feel positive again so going to fit new thermostat and water pump kit and put it all back together and try it out, hopefully got away with it ... Cheers :-)
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Old 04 September 2015, 03:34   #44
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Originally Posted by paintman View Post
If it's a chap in need of some mozzy spray I think we've been looking at the same youtube clip
If one cylinder was very low - as his was - I'd be repeating the test after putting some oil into the cylinder. If the reading then went up I'd suspect rings/bore/piston damage.
I've also been looking for a service manual for yours online, lots of owners manual that just give compression ratio free to download but the service manuals generally are on pay-to-download sites - - although I've just checked the service manual for mine & it makes no mention of compression test results.

If your plugs were older a steam cleaned look is a giveaway that a cylinder has had water into it.
Difficult to know which way to go, but in the absence of any other suggestions - or the problem having gone away after what you've done so far - I think the next step could be to remove the head & examine the bores & the state of the gaskets.
that's him mate you could hear the little buggers
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Old 04 September 2015, 03:38   #45
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I'm starting to feel positive again so going to fit new thermostat and water pump kit and put it all back together and try it out, hopefully got away with it ... Cheers :-)
Fingers crossed!
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Old 04 September 2015, 03:46   #46
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thanks found it, I download the large Yamaha/mariner file and found the figures at last... Section 6-147

Minimum compression =175.4
My gauge isn't decimal place accurate but the needle was on the good side of 175 so looks like it's all ok :-)
hi Ron
that's good news just had a look at my service manual i know its four stroke but as a comparison cranking with recoil starter 71-142 psi with starter motor 71 - 256 psi 25 hp Suzuki and 14 psi difference between cylinders so i think your right on the money apart from getting the water ways cleaned out i would give them a good blow out whilst the bottom of the leg is off to remove any loose stuff especially if its been stood, then give it a run with salt away or another de-scaling product.

cheers
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