Yamaha 70BET0 idle issue

[Yammie70]

Hi everyone,

Recently, my outboard started to run a bit rough at idle. It often dies after a while.
I don't have the full history but I know that:

- Carb kit installed a year ago + water separating filter
- Sparks plugs are new
- Compression ~95psi on all 3 cylinders. it's a bit low but it's been like this for a while.
- Motor runs well in gear

The motor starts really well (when hot) but the idle is a bit rough (shake).
Sometimes you can hear some sort of a 'pssshit' noise and if I leave running too long it dies.

I've tried to increase the idle screw a little and it does makes things a little bit better (from 30sec to 1min without dying at idle).
Should I increase the idle screw more ? or do you think the problem comes from somewhere else ?

Here is a video of the outboard running, I was hoping someone would have a clue and could help diagnose the problem,
thanks!

[boscoe99]

Need an engine serial.

[Yammie70]

The engine is a 70BET0
Serial: 6H3L 489488 W (year W - 1997)

[TownsendsFJR1300]

Sounds like an misfire every once in awhile..

How did the old spark plugs look?

.

[99yam40]

I think it has a lean sneeze going on.
if it runs well after warmed up then at least one cylinder is running lean at cold
may need to go thru the carbs again

did you follow the procedures in the service manual after installing the carbs?
link & sync along the pilot screw adjustment?
did you check to make sure the timing is correct with a light?

[robert graham]

My 1999 c90 3 cylinder 2 stroke similar to yours started idling rough and cutting off a few years ago and I removed each idle mixture screw and sprayed carb cleaner in orrifice where screw was, then followed by some high pressure air hose in same hole, replaced screws setting about 1-1/2 turns out from lightly seated....and it fixed the problem!.... Must have been some trash or debris in those orrifices or circuits.....maybe give that a try....

[Yammie70]

Thanks everyone for you inputs

Sounds like an misfire every once in awhile..

How did the old spark plugs look?

.

The old spark plugs looked OK, I've replace them for peace of mind. When I did the compression test a few days ago, the spark plugs looked fined and they were all the same color

99yam40[/B]]I think it has a lean sneeze going on.
if it runs well after warmed up then at least one cylinder is running lean at cold
may need to go thru the carbs again

did you follow the procedures in the service manual after installing the carbs?
link & sync along the pilot screw adjustment?
did you check to make sure the timing is correct with a light?

.

I didn't install the carb kit myself, but I assume a tuning has been done afterward. The motor was running really well for at least 50-80h after carb kit was installed.
I didn't check the timing because I don't have any gauge or light to do so, but I will try to find one.

robert graham[/B]]
I removed each idle mixture screw and sprayed carb cleaner in orrifice where screw was, then followed by some high pressure air hose in same hole, replaced screws setting about 1-1/2 turns out from lightly seated

That sounds like a good option, I think that will be my next step.
Do you know where I can find the correct number of turns for adjusting the screw ? I didn't find anything about this in the owner's manual and there is nothing inside the cowling either.

Thanks again everybody

[HarrisonDawgs]

Since I just went thru erratic idle I will suggest you at least check your thermostat just for giggles. May not correct your problem but good maintainence anyway. Does sound like a lean mixture though.

[Yammie70]

Thanks, I replaced the thermostat last month so I think we can rule this one out.

[99yam40]

Thanks everyone for you inputs



The old spark plugs looked OK, I've replace them for peace of mind. When I did the compression test a few days ago, the spark plugs looked fined and they were all the same color




I didn't install the carb kit myself, but I assume a tuning has been done afterward. The motor was running really well for at least 50-80h after carb kit was installed.
I didn't check the timing because I don't have any gauge or light to do so, but I will try to find one.



That sounds like a good option, I think that will be my next step.
Do you know where I can find the correct number of turns for adjusting the screw ? I didn't find anything about this in the owner's manual and there is nothing inside the cowling either.

Thanks again everybody

Service manual will have the specs.
but then you could check them before removing.

[robert graham]

I believe that the screws are set about 1-1/2 to 1-1/4 turns out from lightly seated......maybe adjust each one slightly in or out for the smoothest idle..... As I mentioned I set mine at about 1-1/2 turns out and my motor idles just fine( for an old 2 stroke) anyway.....

[99yam40]

I believe that the screws are set about 1-1/2 to 1-1/4 turns out from lightly seated......maybe adjust each one slightly in or out for the smoothest idle..... As I mentioned I set mine at about 1-1/2 turns out and my motor idles just fine( for an old 2 stroke) anyway.....

but yours in not a 70

does your service manual have specs for the 70 and 90?

[robert graham]

My Clymer manual says 1 to 1-1/2 out from lightly seated for the 70 and the 90.....

[99yam40]

maybe that would be 1 1/4 +or- 1/4 in a Yamaha manual

[robert graham]

It ain't brain surgery anyway.........