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HK

wrote:
On Wed, 26 Mar 2008 09:46:26 -0700 (PDT), wrote:

On Mar 26, 1:29 pm, wrote:
On Wed, 26 Mar 2008 08:17:41 -0700 (PDT), wrote:
What about the fact that you may well be voiding your warranty? What
about the fact that today's fuel systems work on precise pressures and
an extra filter may very well change that? What about the fact that
the computer my very well sense a problem with the fuel delivery and
not work correctly?
There are two fuel pumps between the line and the injectors. I doubt
an external filter will have any effect at all.
It HAS to have an effect, it's a restriction.

The question is really whether it affects performance and it shouldn't
unless the filter is plugged. That is a lot more likely in the tiny
little filter on the engine than a big spin on.
Considering they use the same basic fuel pump on the primary side as
they used in ther 2 stroke which used a lot more fuel, it should
deliver plenty to the second stage metering pump.
I looked in my Merc shop manual and it is silent about external
filters. It does warn about anti-siphon valves causing lean conditions
and electric pumps causing overpressure problems.
I have had a Racor spin on installed since the late 80s on my boat and
from my exoerience they rust and leak long before they plug up. I
stopped buying the sight bowl model because it is more expenbsive and
I have never had a water in the fuel problem. I use my boat a lot so
condensation is not really an issue. The regular spin on still
separates water and I suppose I could spin it off and dump the water
out if I did get some. So far I haven't.

I know a few guys with the RACOR filters on their outboards, including
some who use Yamahas. I don't know this for a fact, but I have read that
RACOR produces private label filters for Yamaha.

Yamaha has a stainless steel mounting head unit available now that the
filters spin into, as it were. Uses the same filters. You can also get
a unit with a water-sensing probe that signals a multi-use instrument on
your boat's "dash." I'd bet other motor manufacturers have these options
available, too.

My feeling is that use of a proper external filter with a modern
outboard is not an issue except to those looking to make it one.