[Rhodes22-list] Is there anyone out there who can help mewith my Yahmaha 9.9 4 stroke

[Michael D. Weisner]

Joe,

This is a bit long but I thought that it might help explain what goes wrong 
in small engines that a handy person should be able to troubleshoot and fix. 
Those of you who have never had an engine fail to start, especially when a 
few miles out, and never expect to, can skip this.

I used to work on engines in a lawnmower/snowblower shop as a kid.  The most 
common problems with small gas engines was usually fuel related.  Yes, I 
changed plugs, points, condensers and even retimed many engines, but hard 
starting was almost always due to failure to maintain the fuel system or 
trying to use old fuel.

First, all fuel should be stabilized if older than a few weeks.  This has 
been discussed recently.  Very little stabilizer is really needed for our 
small quantities of gas.  More is not necessarily better.  Stabilizer keeps 
the "punch" in gas and emulsifies water so that it can be burned.

Next, small leaks in fuel systems are real hard to find.  They usually leak 
air into the line, not gas out, thereby preventing proper drawing of fuel to 
the point of combustion.  Replace worn or damaged hoses and use good clamps 
to insure a tight fit.  Check and replace filters and their connections as 
well.  Make sure that the carb screws are tight and that the bowl is not 
leaking.  If you feel adventurous (this requires some mechanical skills), 
you may want to open the bowl and make sure that the float is not sticky due 
to gum and varnish.  This can create a problem of too much or too little 
fuel depending on whether it sticks open or closed.  The best way to avoid 
this situation is to run the engine regularly (monthly) or to be sure to run 
it dry before seasonal storage.  A replacement bowl gasket is generally 
required.  NOTE: The fuel needle valve is fairly delicate - if you don't 
know what you are doing, you may cause more damage inside the fuel bowl if 
not careful.  Also, you must be meticulous in your cleaning since anything 
(sand or crud) in the bowl WILL ENTER THE ENGINE.  There is no filter 
between this point and the internals of the engine.

It is fairly rare for the fuel pump to fail, although it does happen.  Much 
more often, fuel is not "sucked" into the system due to a small leak.  If 
engines only run at high throttle, it is usually related to failure to draw 
fuel with lower suction at low rpm, although it can be related to low fuel 
pump pressure.  With outboards, the ability to draw the fuel may be impeded 
by the creation of a vacuum in the tank due to a closed or clogged vent.  If 
opening the gas filler cap solves the problem, look for a clogged vent.

With outboard setups, we also need to check the hose from the tank and the 
primer bulb for leaks (usually cracks in the bulb) and to make sure that it 
still pumps, since the valves inside are plastic and do fail.  If the motor 
doesn't start at all or only runs for a minute or so, check to see that fuel 
is getting to the engine by watching the fuel filter fill with gas when 
pumping.  If the filter is not see through, you may need to loosen a clamp 
to verify that gas is present.  Sometimes the fuel hose inside the tank 
collapses or becomes clogged.  Be sure to clean up and spilling gas before 
starting to prevent fire.

If fuel is getting to the combustion chamber but the engine doesn't run or 
runs poorly, check to be sure that air is reaching the system properly.  The 
air filter may be clogged or the choke may be stuck (closed or open.)  The 
choke partially closes off the air intake during starting to make a rich 
mixture for easier starting.  Once started, the engine will stall if the 
choke does not open (manually or automatically.)  Some outboards use a 
bimetallic spring to open the choke when the engine warms up.  If this isn't 
working properly, the engine may fail to start due to an open choke when 
cold,  If the spring fails to open when warm, a very rich mixture will cause 
poor acceleration or missing as the throttle is opened.  Some older 
outboards had problems running at high speed only with their covers replaced 
due to the fact that the air filter was in the cover and was clogged.

You can remove the spark plug wires and check for the presence of spark 
while cranking, although you should learn what normal sparking is like when 
the engine is OK, not when it is broken.  Ignition testing is a bit more 
difficult and should be left to a mechanic.

I hope that this has (or will in the future) helped someone.

Mike
s/v Shanghai'd Summer ('81)
Nissequogue River, NY

From: "Joe Babb" <joe.babb at comcast.net>Sent: Monday, August 11, 2008 5:44 PM
> Hi Alice,
> I'll be curious to know what you find out.  Our used 9.9 is getting
> harder to start, but still runs okay once it is started.
> I tried looking in my 9.9 service manual for hints but like most
> "troubleshooting" guides, it was useless.
> Since it does run, it's getting some gas, but it might be worth checking
> the fuel filter.  This is an inline afair.  Take off the
> cowl and follow the hose from the gas connection to the fuel filter.
> Not much of a way to test it other than replace I'm afraid.
> The other thing to check is the spark plug to see if it is fouled.
> Let us know the outcome.
> Joe
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