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looking for some free advice i have a 40 hp yahama 2 stroke outboard took t out for a shake down cause weather may turn around some day and it gave me a problem running it is a 3 cylinder it ran like it was running on two cylinders 3800 rpms out of a 4500 as it normally does last trip out was early dec. no problems does have ethonal gas in it what do i look for i took each plug wire off by them selves and it fired up each time does any one have any advice what to look for before it goes to an expensive shop
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Same motor same issue
I have a 2000 40hp Yamaha I found when I reinstall my cover the top plug would kinda pull off.
Then mine stated doing something simular. However mine was kinda surging from fast to slow like as if it was running out of gas. I stripped down my carbs cleaned them and put fresh (non ethanol) gas back in. I went for a test run and it was running as if it were 2 cylinders. Next time I ran it my bushing in my prop went out. I had to idle back to the dock.
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carbs
I helped a friend with the same sort of problem on a 50 yamie, his carb jets were full of trash from sitting with ethonol. It doesn't take long. Check your carbs. It's not hard if you are a little mechanically inclined. Just pay attention when you pull the carbs to clean them. Take pics of before take=down for reference.
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Good tip
Also if you never tore down a carb before here's a tip for cleaning the jets. Mark the slot on the set screw to the carb screw in and count each turn before backing out. Once you clean the jet screw it all the way back in and count the same amount of turns out. You should have no problem.

Also after I cleaned my carbs I ran sea foam as per the directions on the can. That did an awesome job of getting the rest out!
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40 Yammie
Also the ethanol gas will melt the inside of a regular gas line to the motor, then it will go to the carb's.
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carbs
are there any manuals on this 40 hp yami beter than others looking on ebay
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Carbs
Theirs nothing to it man take your 3 carbs out keep them in order clean the jets..take the top plate off you'll have to little things that look like dimes clean them real good and spray all your holes with card cleaner and air compressor
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Repair
My 90 Merc did same thing a couple years ago after running ethanol gas in it. I ended up getting rid of left over gas, changed gas lines and fuel filter. Took off all three carbs and cleaned them good using Sea Foam. It went back to running good after that. I also add sea foam to my tank if its going to set up for more than a month.
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carbs
i guess seafoam will do the job i just cleaned out my diesel truck with it
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Ethanol
You might want to give the fuel pump a look as well. My 1995 Merc 150 was surging when trying to jump on plane but would run fine at idle or low speeds. All 3 of my carbs had been reworked previously. Changed all my fuel lines and then took apart the fuel pump and found this inside of it!!Hope this helps!!
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big thanks
thanks to all that responded thanks jarret did not think of that thats a lot of crap in that pump boughy seafoam and plugs today also a instruction manual will do this after this cold snap
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