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Discussion Starter · #1 ·
Hey Guys

I have an old mariner 15 that I put on my IPB 14, it was running pretty good until last night. After cruising all day running from spot to spot turning the motor on and off at least a dozen times i was idling around while talking on the phone. The motor ended up stalling out and it took about 20 pulls to get her started. Even then when it turned over I had to immediately put it in gear and run back to the dock where it stalled again. Now I can not even get it to crank and stay running.

Here are the things I have done recently to the motor / Before it started acting up again.

New Carb
New Sparks
New foot oil
New Gas & Oil
New Fuel filters

Not sure if it was related but it was also giving me a little squeal almost like belt noise on a car but not as loud.

The water pump is pumping water and compression is 110 on both cylinders.
 

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Discussion Starter · #3 ·
well... the motor year is impossible to find. The motor was made during a period when the SN did not mean anything. From what I find it is a late 80's early to mid 90's.

It will fire on occasion but will not stay running
 

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I love my microskiff
1998 Action Craft 1890- 2019 Yamaha f150- gen1 AC Factory leaning post/standing helm station
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You have trash in the carb, I would guess. These small jets in the carb mean that a small piece of trash can cause a big headache. It was cranking and running so you know you have spark. Make sure the fuel is clean and fresh- we have been getting a ton of rain, so ensure the tank doesn't have any water in it.

Get a high quality spray carb cleaner like Mercury PowerTune or similar. The stuff is like gap-filling foam and is amazing. Disconnect your fuel line and fill the carb with it- don't be shy. Then pull it through with a couple of yanks on the cord. Spray more. Let it sit for 45 mins. No longer than an hour, anyway. Then brace up for some pulling. Pull that cord till the engine fires, or at least till you have pulled fresh fuel all the way through it. If that does not work, you are going to have to pull the carb off and detail clean it.

Keep us posted.
 

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Living & Dying in 3/4 Time
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Sounds like what my old Johnnyrude did with a dirty carb. What float is in the carb? New plastic or old cork? Do you have a fuel water separator on the boat?
 

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well... the motor year is impossible to find. The motor was made during a period when the SN did not mean anything. From what I find it is a late 80's early to mid 90's.

It will fire on occasion but will not stay running
I realize sn# doesn't identify the year, but it does let you reference the schematics for the correct model. Probably doesn't matter in your case, since 2-cycle mercs were pretty similar from the mid-80's unit they stopped producing them.

Are you sure you're getting spark consistently? Is the plug wet if you pull it right after cranking it a few times? If it is, you can pick up a cheap spark tester from most auto parts stores. Once you figure out whether it's fuel or spark that isn't making it to the cylinder, you'll know where to begin.

Hate to say it, but it could always be an ignition problem. I recently had a bad control box that would only barely fire one cylinder. It was a very deceiving problem.
 

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Rules for diagnosing a 2 stroke outboard,

1) Check Compression
2) Check Spark
3) Check fuel

Also when you pull the spark plugs to check the compression inspect the plugs it will tell you if the motor is running lean, rich, etc, etc.

Can a Mod Make this a Sticky!
 

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Discussion Starter · #9 ·
No fuel water seperator, only have a 3 gal tank so the fuel is replaced often.  I have not put the spark plugs in any kind of tested but when I pull them out and place them close to the cylinder I am getting spark when I try and fire the motor. Plus they are brand new plugs.

What are the indications on a spark plug that let you know if you are running lean or rich? Fuel ration right now is 50:1.

SN is 684c S 044871
 

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I would pull and clean the carb. As a test find a dropper pull the plugs put a cuple drops of gas in each cylinder then reinstall plugs work fast as gas evaporates and don't pour a ton in or you will flood it. pull, if it will fire for a second or two I would start with the carb then move on to the electrical side of things.  I do not use sea foam or the other junk additives for cleaning a carb. on small motors it's worthless. the only way to clean the card is to pull it completly apart and clean everything including the passages(tiny holes.) I have had to many friends bring their motors to my house claiming to have cleaned the carbs I clean them and it's like a mirriacle they suddenly work again in most cases.  same with lawn mowers, weed eaters, chain saws...

My experiences with CDI's and condensers is as they get hot they stop working. and usually one cylinder will starts having issues not both. On twin cylinder motor you should be able to pull a plug boot and the motor will continue to run at high idle on one cylinder, albeit like crap. this is A poor mans test for determine if a cylinder is getting good spark if fuel supply problems have been ruled out.
 

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Discussion Starter · #15 ·
Got the motor back today.

Turns out that it was a dirty Carb. The guy showed me all the deposits that came out of it and it was amazing how fine the particles were. Almost like super fine metal filing dust.

Replaced the onboard fuel filter and added another inline from the tank to the motor. Seems to run fine with the muffs on. Tomorrow will be the real test when I get her in the water.
 
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