Re: Fuel pump and filter mystery

On Tue, 30 Oct 2007 14:22:32 -0400, "Roger Long"
<strider@xxxxxxxxxxxx> wrote:

It's a Yamaha 2QM20. The bottom of the tank is above the engine fuel pump
but the fuel line was run to about level with the top of the engine. The
primary Racor 200 (discontinued) used to be fairly high but I moved it down
to the bottom front of the engine bed where it is easy to inspect and
replace. The electric pump has always been there but I'm going to look
carefully at the system this winter and see if I can eliminate it by
rerouting the fuel lines. I would still keep an electric pump for bleeding
and in case the diaphram on the engine driven pump fails.

The secondary filter is at the top of the engine. I'm running 2 micron
elements in both filters. I think the fuel system is pretty clean because
there was not so much as a speck in the fuel I drained out of the sediment
bowl or the bowl for the secondary. I've used nearly 200 gallons of fuel
this season and bounced around a lot.

A vacuum gauge for the primary is on the list of improvements this winter
but the problem this time seems to have been the secondary. It is
downstream of both pumps so I can't put a gauge on it.

I'm not entirely sure that either filter was clogged. The process of
replacing the secondary and bleeding the system could have dislodged
something else.

First of all, if the diaphragm on the engine driven "lift" pump fails
it provides an opening between the fuel side of the pump and the
mechanical side. Usually resulting in a rapid increase in crankcase
oil level.

Another point: when you say you have a 2 micron filter, unless you
have something other then the normal fuel filter, what you have is
actually a filter with an average of 2 micron filtering (if half the
filter was solid and the other half with 4 micron density the average
would be 2 micron) so it can pass larger then 2 micron particles.

I have no idea how frequently you change filters but it is certainly
possible for the primary to be passing particles which are caught by
the secondary and ultimately both filters clog.

A short story here: Some years ago I had the occasion to rebuild my
venerable Perkins 4-107. As long as I had the engine apart I took the
injectors and pump to a pump shop to have it calibrated and the
injectors checked. When I came to get them the bill was $100 which was
a substantial amount of money in Singapore at that time. I asked the
guy "Wazzat?" and he handed me the pump plungers and pointed out the
wear. "Change the filters", the guy says. "But I got good filters",
says I. "Change the filters!"

So, since that time I have religiously drained the bowl on the primary
before starting the engine and changing both filters with every oil
change and (Knock on wood)have had no problems since.

Re: Filter gages. Use a suction gage on the outlet of the primary and
a (low) pressure gage on the inlet of the secondary.


Bruce-in-Bangkok
(Note:displayed e-mail
address is a spam trap)
.

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