YS FZ91 Problem
Henderson,Eric
Eric.Henderson at gartner.com
Thu Jan 29 07:21:02 AKST 2004
These are always tough to answer and, although I have two of them, I don't really feel that I have the knowledge base that I have with the 1.20-1.40.
The servo and fuel line sound like good suspects. Also look for tank pressure after the run is over.
I did have some idle problems. I believed it was the diaphragm but did not have a spare for the 91. In the end I fitted a complete regulator assembly from a YS 1.20/1.40. It worked. Looking at the 91 diaphragm it is different in that it is a one piece gasket and diaphragm combo. Two of mine were pretty distorted. Central Hobbies has the spares.
You can test the engine on the ground. Use a minimum of 20% nitro and a fresh OS "F" plug. It should idle for at least a full five minutes. Pick up the plane and hold the nose up. It should keep running and maybe speed up a fraction due to the leaner feed. Point the nose down at about 20 degrees to level. Should still idle but a little slower. If it does all of these things right the idle is right. If it quits with nose up it is too lean. If it quits with nose slightly down it is too rich.
So how do you set the idle. That screw is more of a transition screw than an idle adjuster. It need to have a reasonably correct fuel flow to work. The YS at idle will actually draw fuel without pressure. The regulator prevents too much fuel reaching the engine at idle. I set my idle with the regulator.
Start with Main needle at approx. normal position. Tank fully pressurized. Engine warmed up. See if it will hold an idle. Turn in for lean and out for rich, about a 1/16" of turn at a time. If idle is good, reset main needle. May be leaner or richer depending upon what you do to the regulator. Then you can set the transition mixture.
Good luck,
Eric.
P.S. Where are you??
-----Original Message-----
From: discussion-request at nsrca.org
[mailto:discussion-request at nsrca.org]On Behalf Of Ed White
Sent: Thursday, January 29, 2004 12:11 AM
To: discussion at nsrca.org
Subject: YS FZ91 Problem
Folks,
We have a club member who is really interested in
pattern and bought a ARF pattern plane and put a YS
FZ91 in it to fly Sportsman and Intermediate. The YS
has been a problem since he bought it. It starts
easily and runs great on the ground, idles beautifully
before take-off, has good power in the air and flys
the intermediate sequence well. Then he sets up for
landing and on the downwind or base leg the engine
quits. I don't mean occasionally quits, I mean every
stinking time.
This is a very low time engine and the only time I've
seen it land under power was when the throttle linkage
slipped and he couldn't make it idle. We've checked
for pressure leaks, run the same magnum fuel I use in
my FZ140, tried the idle leaner, tried the idle
richer. He sent the engine back to YS who installed
an "updated" piston. All to no avail.
I finally got him to give me the engine to tear down
and look at. I haven't got very far into it, just
pulled the valve and airbox covers and diaphragm. I
was sorta hoping to find an air leak but so far
nothing obvious. Any thoughts/experience from the
community?
Thanks,
Ed
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