Re: [OMC-Boats] cowling venting

Hi Jeff

The spark arrestor, actually a backfire flame arrestor, is also the air
intake - there's just no replaceable filter involved. It's required by the
Coast Guard on all boats with an engine that could backfire, which, besides
being noisy, shoots flames out of the carburetor.

Gas fumes are heavier than air - which is why the blower intake is at the
bottom of the bilge and why the scoops have 3" hoses directing the incoming
air to the bottom of the bilge when underway. Explosions seem to be rare
and probably involve a fuel leak with lots of gas sloshing around down
there - any experience in this group? (!)

The rumble of that oddfire V6 with the tilt up a little brings a smile to my
face every time...

-Doug Julien

----- Original Message -----
From: "JEFF DOOD" <jdood@...>
To: "Evinrude & Johnson Boats of the 1960's and 70's"
<omc-boats@...>
Sent: Tuesday, July 22, 2008 10:34 AM
Subject: Re: [OMC-Boats] cowling venting

> AH - ok, makes sense now. although diminishing noise seems to be the
> least concern with about 1/2 the boats i see (hear) at the boat ramp
> every time.
>
> and so if the thing on top is a spark arrestor, not an air cleaner,
> where do these engines get their air for combustion - shouldn't there
> be an intake somewhere? not disputing, just wondering
>
>
> so i guess i could put a grill in my cowling, and it would just be
> louder and maybe a little less likely to explode on starting due to
> better fume venting. but it won't run any cooler!
>
> actually another question - are gas fumes heavier than air? if
> so, where i want to put the vent won't help the fumes at all. either
> way, i always run the blower regardless.
>
>
>
>
>
> On Jul 22, 2008, at 7:03 AM, D. F. Julien, AIA wrote:
>
> > Hi Jeff
> >
> > Engine noise is probably the reason for the tight compartment. If
> > you put a
> > grille in the back cowling, facing forward, you'd greatly increase
> > your
> > awareness of the engine noise.
> >
> > Not that it changes your argument, but that round thing on top of the
> > carburetor is a spark arrestor, not a filter. I guess the
> > presumption is
> > that boats don't go down dusty roads much during operation.
> >
> > -Doug Julien
> >
> >
> >
> > ----- Original Message -----
> > From: "JEFF DOOD" <jdood@...>
> > To: "Evinrude & Johnson Boats of the 1960's and 70's"
> > <omc-boats@...>
> > Sent: Tuesday, July 22, 2008 12:19 AM
> > Subject: [OMC-Boats] cowling venting
> >
> >
> >> kind of inexperienced with boat i/o motors. here's something i
> >> don't get.......why no venting in the cowling? i happen to
> >> have a
> >> Deluxe, but i think it's the same story with other boats as well.
> >>
> >> - You are supposed to vent the fumes out with a blower before
> >> starting.
> >> - the top of the carb has an air cleaner intake just like a car
> >> (although small)
> >>
> >> yet my particular cowling seals up pretty tight and seems like it's
> >> designed to not let any air get in. it does have a smaller grill in
> >> the back of the engine compartment, but minimal. So why aren't
> >> cowlings (or atleast mine) vented like crazy with air grills all over
> >> the place? it just seems like it would A) make the engine run
> >> better
> >> by providing more available fresh air intake, B) make the engine run
> >> even cooler with air flow taking away some of the heat , and C) make
> >> it easier for the accumulating fumes to get out of the cowling
> >> without
> >> having to rely on the blower.
> >>
> >> I have a perfect spot right on the front of the cowling for a nice
> >> big
> >> chrome vent, but i don't want to be cutting any holes without knowing
> >> for sure first.
> >>
> >>
> >>
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> >
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Received on Tuesday, 22 July 2008