[NSRCA-discussion] OS 120 AX

[J N Hiller]

Bob. I have two 120-AX purchased at different times. The carburetors were
different. On one when the barrel is fully open the idle mixture needle
pressed into the barrel didn’t fully withdraw from the idle adjustment /
fuel delivery tube.  The other had about .03” gap between them. I modified
the idle needle in the first one and it has improved. I am running a 16-10
APC about 8500 and I am not totally happy with the transition. I am using an
OS #8 plug and have not yet tried the ‘F’. Transition lags, I think due to
the engine cooling off at mid throttle. Lower nitro 10% seamed to work
better allowing a leaner high speed setting without excessive heat buildup
in a prolonged vertical with the heavy load. I felt like higher nitro fuel
needed a head shim, which I haven’t tried yet. I tried the 16-8 prop and
didn’t like it. It took a higher throttle setting in horizontal flight than
I like. It may also help to restrict the exhaust outlet of the stock muffler
also to increase muffler / fuel pressure at full throttle, which I haven’t
tried yet either. I don’t get along with pumps and have learned to start
getting into the throttle with elevator every time I go vertical. I am
flying a 9 lb 4 oz airplane in Advanced which I believe is pushing the limit
for this set-up. Sorry for the late post but I just got home.
Jim Hiller



-----Original Message-----
From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of Bob Richards
Sent: Monday, September 03, 2007 5:35 AM
To: NSRCA Mailing List
Subject: [NSRCA-discussion] OS 120 AX

I acquired a plane with an OS 120AX installed, and seem to be having some
issues with it. It came with an APC 16x8 prop and stock muffler. Is not
running as well as I think it should, but I did figure out I had some bad
fuel. I plan to go out again today and tinker with it some more.

What fuel, prop, and what rpm figures should I be seeing?

Thanks in advance.

Bob R.

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