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Old 10-21-2013
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Default Fuel leaking from carb

Looking for advice please. I have a Yamaha 85 aet pre mix power trim motor. I have found it has become very heavy on fuel. There is quite a bit of fuel mix ( the fuel that runs out is quite substantially oily) running out from the front of the carbs if I tilt the motor say when we get to a shallow area and switch off. The motor also runs on after switching off the ignition for around 5 to 10 seconds.
I am mixing oil fuel 50:1. shell nautilus

For example we ran around 5km or so on the weekend . Some at 4000 rpm and some around 2500rpm from spot to spot fishing. We used around 10 to 12 litres of fuel.

Any help please.
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Old 10-21-2013
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Your floats are probably saturated and are sinking,,, time to tear them down and inspect/rebuild,,
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Old 10-21-2013
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Quote:
Originally Posted by 85aetyamahauser View Post
Looking for advice please. I have a Yamaha 85 aet pre mix power trim motor. I have found it has become very heavy on fuel. There is quite a bit of fuel mix ( the fuel that runs out is quite substantially oily) running out from the front of the carbs if I tilt the motor say when we get to a shallow area and switch off. The motor also runs on after switching off the ignition for around 5 to 10 seconds.
I am mixing oil fuel 50:1. shell nautilus

For example we ran around 5km or so on the weekend . Some at 4000 rpm and some around 2500rpm from spot to spot fishing. We used around 10 to 12 litres of fuel.

Any help please.
not sure what kind of boat you are running, but running at 2500 you probably get less than 2 MPG, and 4000 maybe around 4MPG but depends on the load you are pushing and how it is propped
Look at this site to see if you can find something close to what you have and see what kind of performance they got at different RPMs. 90HP will be close to your 85 is my guess
Performance Bulletins | Yamaha Outboards

When key is turned off the spark should not get to the plugs so should not keep running, that is one of your problems you need to look into

when running some fuel mix spits out of carbs and collects in the silencer on front of carbs, when the fuel evaporates it leaves a real oily residue that may be what you are seeing when you tilt motor

Last edited by 99yam40; 10-21-2013 at 09:09 AM.
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Old 10-21-2013
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Thanks Sequoiha. I will pull them off and check. The fact that the motor still runs on makes me think there is carbon build up in the cylinder to ignite the fuel as well as fuel mix in the plenum chamber of the intake perhaps. I was contemplating lowering the oil mix slightly as we never really run at top revs. Any advice...
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Old 10-21-2013
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I would stick to what Yamaha recommends.

Need to decarbonize motor if it has a build up in it
Yamaha makes Ring Free and a combustion chamber cleaner that should help

Not running to the upper RPMs and not propped properly can cause carbon build up along with quality of fuel

Need to make sure the key and kill switch are grounding as they should and the plugs are not getting spark when they tell it to turn off.
Fuel in carb bowls will keep motor running if the cylinders are firing even if there was no extra fuel in silencer( what you call plenum chamber of the intake)

Last edited by 99yam40; 10-21-2013 at 10:56 AM.
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Old 10-21-2013
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Until you get the problem (possible dieseling), solved, turn the engine switch off while STILL IN GEAR..

The extra load of the prop against the water should stop the engine immediatly (if dieseling/pre-ignition).

If it keeps running, as posted above, your ignition is probably still producing spark.
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Old 10-23-2013
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Default Re advice

Thanks to all for your advice. I will give feedback as to what I find. You have all been a Great help Thank you.
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