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Old 15 June 2015, 04:20   #1
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Country: UK - England
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Running a Mercury 50 ELPTO without an air box.

In between having my engine serviced, carbs removed and ultrasonically cleaned my air box seems to have gone missing. I thought I'd acquired a replacement via ebay but it doesn't seem to fit.

Is there any harm in runnintg the engine without the airbox?
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Old 15 June 2015, 05:48   #2
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For those not aware this is an autolubing two stroke.
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Old 15 June 2015, 10:48   #3
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Quote:
Originally Posted by Tim in Yorkshire View Post
In between having my engine serviced, carbs removed and ultrasonically cleaned my air box seems to have gone missing. I thought I'd acquired a replacement via ebay but it doesn't seem to fit.

Is there any harm in runnintg the engine without the airbox?
I am not an outboard mechanic, I am an automotive hobbyist.

But, the way it has always been explained to me:
Small engines typically have "tuned" airboxes which provide a certain amount of restriction at certain points in the RPM range. The engine may run lean or rich without the factory designed airbox, with a loss of power and possible engine damage.

I would recommend replacing the airbox.
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Old 15 June 2015, 12:33   #4
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Click image for larger version

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This is what's on the side of my engine which is a 40HP versions of yours.
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Old 15 June 2015, 16:27   #5
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Thanks, looks like I need to find a new one then.
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Old 16 June 2015, 08:04   #6
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Part ordered, it won't arrive in the UK until next week, so I'll launch the boat on to its mooring at the weekend then leave it there, all under 3000rpm of course!
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Old 16 June 2015, 08:58   #7
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If you run a 2/str without its air box, keep the revs to a minimum,because if you rev it up it will run weak and can/will cause overheat and power head damage. Ive seen o/heat damage many times through running on a weak mixture.
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Old 16 June 2015, 18:11   #8
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At risk of playing devil's advocate / genuine question - I would have thought the carb would throw in as much fuel as the air passing through it would pull out the carb bowl by the vacuum through the venturi?

Therefore would the fuel not be mixed correctly, albeit at not the passing volume it was designed for? (i.e the mix stay Ok-ish even if not as efficient through the intake passages / carb etc).

I will happily bow to Uncle Al's superior knowledge, but I have run the Merc happily minus the air box lid as it was a PITA to remove it every 2 mins to adjust the idle screws! (Granted I run premix so over oiled a lot of the time....)
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Old 17 June 2015, 04:24   #9
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It is to do with the bends and curves of the air box and the air flow to the throut of the carb. A long long time ago an engineer explained it to me. I have to admit most of it I have forgotten, I just remeber the bare bones now, (cos Im Old)but remember the powerheads that I had to repair/re-build because of running mostly at high speeds on a weak mixture.
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