yamaha 80 running rough

[one eye]

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.

[Jizm]

Welcome to ribnet.

What is the year and model no? as it will help.

[Nos4r2]

It might be limiting the revs because it thinks you're trimmed too far out. Check all the trim position electronics.

[one eye]

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

[Nos4r2]

Depends on the engine. My 85 doesn't sound fantastically smooth at tickover but runs beautifully.

[Chris]

Are you running it up on flush muffs cause if you are it will sound quite rough.

Chris

[one eye]

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

[Nos4r2]

Originally Posted by one eye

Will it run smoother in the water?

Yes-much.

Originally Posted by one eye

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.

Originally Posted by one eye

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.

[one eye]

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

[Nos4r2]

Pretty much. Just shorten the blades til you have to use full throttle to hit 5000 revs. Make sure you don't unbalance it.

[fast fred]

she's lookin for 8deg' on the slow side, and 20deg' max on the high side.