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Early 90’s Mariner 6hp 2stroke low compression?

7

7tenths

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I’ve just picked up this motor for the kids (and me), to put on a 10” tinny. I checked the compression and it’s down to 60psi both cylinders (cold). Does this indicate a re-build is necessary (or rings at least)? It’s been sitting for about 3 years and isn’t actually running at present (prior to that it was running fine, so I suspect fuel pump or carbi as it fires up straight away with a squirt of fuel into the cylinders, but only for a second or so. I know I shouldn’t do that with a 2 stroke, but just needed to prove a point). Seems there’s very few parts available for these - I guess people just throw these little ones away, but I really don’t want to do that if I can avoid it. Any thoughts be greatly appreciated.
 
Suggest you get it running for several minutes (or longer) somehow, then check the compression again. If it comes up to about 100 pounds, she should be okay.

Jeff
 
It’s not running yet, not getting any fuel through. But the guy I got it off said it ran really well and I used to see him out in it.
 
Managed to get it running. Pretty rough though, but got it warmed up. Re-checked compression, cyl 1 at 58psi, cyl2 at 52psi :(
So looks like a re-build, but is it worth it? Had a quick look on line, doesn’t seem to be lots of spares available. Is this something I should I attempt myself though? I have mechanical experience, just not outboards though. Sorry for all the questions.
 
Might not trust the gauge....maybe low. Try the gauge on your chain saw. Most modern saws are 130 to 150 psi. My near new Jonsered 630 is 140. This gauge I have is quite expensive and 45 years old. I have checked it on hundreds and hundreds of motors. My readings seem a bit lower than what other techs like to see on these motors.....not sure why, but rarely do I see anything above 80 or 90 on these little twins......note: Try the same test with throttle open, see if it makes a difference. Regarding rebuilding, you should be able to get parts there reasonable, if not, then I'll price them out here.
 

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timguy said:
Might not trust the gauge....maybe low.
Click to expand...
It was a brand new gauge so didn’t think of that, but I just tried it on my car, it registered 115 which I know is not right as I know it is around 145. So went and borrowed another gauge - car 140, and o’board now registering 85 on cyl1 and 82 on cyl2. So much happier with that and will hold off in the re-build and see how it runs.
I now have to fit new impeller (very weak telltale), and carbi kit. Hopefully be good to go then.
Thanks again for your help.
 
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Fitted new impeller today and managed to get it started. Nice strong telltail, but the little bugger won’t stay running. It starts second pull easy and if I rev it hard it will continue to run, but as soon as I drop it back to anywhere near a fast idle it just snuffs out. Pulled the carby off and cleaned it thoroughly, but it was nice and clean anyway. All the jets blew through. Put it back on and still same problem. If I keep hitting the primer as it starts to die, it will keep running at idle. Give it a few revs, probably about 2500+ and it will keep running on its own. Checked the idle mixture screw and backed it out (although just had a thought writing this now - maybe I should be screwing it in for richer idle?). Very frustrating - so close to getting it running.
 
Maybe a weak fuel pump....dirty? Make sure all okay with tank too. You say it idles if you keep pumping the squeeze bulb? To test fuel pump a simple way (weakness test), raise tank to above level of the motor and see if it gets enough fuel now.
 
Well after removing the carby for the 4th time, I pulled the reed valve housing out this time. The rubber o section seal that runs around the housing sealing off between the 2 chambers I believe was not sealing as it was very sloppy and couldn’t see how it would seat properly. So shortened it be pulling both ends through the housing so it sat nice and tight in the grove, put it all back together and here’s the result:


Starts first pull, hot or cold. Awesome! Thanks for all your help everyone. I’ve learnt a lot about 2 stroke outboards for sure.
 
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Thanks so much Tim. Once i got it to idle I was then able to adjust the mixture needle to get idling as best as possible. I really think it was a combination of a few different issues. Every time I changed something it would make a difference. Just had to work through everything doing one at a time. It absolutely flies too. Wow, what a 6hp!
 
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