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Old 10 May 2007, 09:30   #1
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yamaha 80 running rough

Please help!
I have just purchased a complete powerhead minus electrics,and replaced on my yam 80,( was told it was a good runner b4 dismantled).
It starts,and idles but above 2000 revs it wont power up and sounds like it fires every 1 second.
I have adusted timing and the three carb screws, checked fuel pump and lines and replaced and set plugs but makes no difference.
What can it be? im stumped and was looking foward to getting out in it this weekend.
Any advice will be greatfully received.
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Old 10 May 2007, 10:37   #2
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Welcome to ribnet.

What is the year and model no? as it will help.
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Old 10 May 2007, 12:24   #3
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It might be limiting the revs because it thinks you're trimmed too far out. Check all the trim position electronics.
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Old 10 May 2007, 12:31   #4
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yamaha 80 running rough

Thanks for your reply.

Just replaced the impeller and insert, ran it up to temp and it seems to be ok now, must have been the rev limiter cutting in on overheat.

I did have water runing out prior to changing the impella, but its comming out smoother and faster now.

Have adjusted timing to 5deg ATDC and done my best to sinc the carbs, it picks up ok but still not that so smooth on idle, (Worked on plenty of cars but this my first attempt on outboards), so not sure how smooth they should be?.

its an 80 AET and i believe its arround 1984.

Thanks Jim
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Old 10 May 2007, 14:54   #5
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Depends on the engine. My 85 doesn't sound fantastically smooth at tickover but runs beautifully.
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Old 11 May 2007, 15:26   #6
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Are you running it up on flush muffs cause if you are it will sound quite rough.

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Old 11 May 2007, 17:01   #7
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yamaha 80

yes chris i am running it on flush muffs!

Will it run smoother in the water?

I have another problem!! I set the low end timing on muffs, Is it safe to check the high end timing on muffs?

It does state in the manual that it should be in a test tank with a test wheel instead of a prop.

What do you think fellas?

By the way thanks for all your replies

Regards Jim
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Old 11 May 2007, 17:20   #8
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Quote:
Originally Posted by one eye View Post

Will it run smoother in the water?
Yes-much.
Quote:
Originally Posted by one eye View Post

I have another problem!! I set the low end timing on muffs, Is it safe to check the high end timing on muffs?
No. It'll bugger your engine if you're unlucky (the impeller will pump more than a tap can supply at anything above tickover) and if you do it without load your timing will be wrong.
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It does state in the manual that it should be in a test tank with a test wheel instead of a prop.
That's the only feasable way to do it. Make yourself a test wheel out of an old prop.
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Old 11 May 2007, 17:29   #9
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yamaha 80

Thanks for that its a great help.

can you explain using an old prop for test wheel?

Do i just shorten the blades?

Regards Jim
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Old 11 May 2007, 17:47   #10
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Pretty much. Just shorten the blades til you have to use full throttle to hit 5000 revs. Make sure you don't unbalance it.
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