outboard air intake design

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catalac08

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as an "outboard engine virgin" I found it quite interesting dismantling the carburretor, fuel filter etc in order to sort a misfire problem (30 hp tohatsu 2 stroke). It was all clean inside no gummy deposits etc and the misfire turned out to be a plug, which I would have done first except that after 400 hrs I felt I should do a bit of maintenance intead of just fixing problems as they occur!
I have had fair regard for tohatsu outboards but I was amazed to find that there seems to be no intake filter for the carburretor, no wire mesh, paper,cartridge - nothing jto stop anything going in to wreck 2/3K of engine, just a plastic cowl and a hole straight into the carburretor inlet.
I always thought that intake filters were an important part of the wear control system - my question is how are other outboards set up or is having no intake air filter just a Tohatsu feature?
 
Outboard engines do not need air filters because they are not normally used on dry dusty roads!

An air intake silencer box is common but not universal
 
Only necessary if you intend to use your Tohatsu on dusty roads.
Not very likely, is it?


edit:
Blimey, too slow!
/forums/images/graemlins/shocked.gif
 
I would agree that none of the outboard motors I have seen has ever had an air filter. It does raise the interesting question of why inboard engines generally do have air filters. Can anyone explain the difference? Is it just that outboards tend to have a short life and are expected to die from other causes before air borne dirt is likely to be an issue?
 
Could be that Outboards normally are expected to operate outside the boat and well clear of any source of dust, while an inboard could easily ingest stuff such as sawdust, grp dust, paint stripping debris, not to mention the odd Fray Bentos, from the inside of a boat.

The again quite a number of inboards are based on industrial engines designed to run in a wide variety of conditions.
 
Some learned gentleman informed me a long time ago, that 40% of engine noise was due to induction roar! and the reason for an effective air filtration system, was to reduce this level. Taking note of these comments, my own instalation has the air filteration intake in the cockpit locker (dry & out of the way) and is significantly quieter than a similar installation with a similar unit. /forums/images/graemlins/grin.gif
 
The familiar and deafening racket of the old Seagull - audible at half a mile range was very largely down to induction noise. Later models had a little plastic silencer cover that did at least reduce the audible range by a few hundred yards!
 
[ QUOTE ]
The familiar and deafening racket of the old Seagull

[/ QUOTE ] Deafening racket! Music to the ears !

Actually even older ones, at least those with Villiers carburettors, could be fitted with a silencer available as an accessory.
 
The ones with a nice long moulded air intake survive better when submerged while running. they stop before the seawater gets sucked into the engine, which makes revival simpler.
Probably quieter as well.
 
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