[NSRCA-discussion] OS 91FX or 120 AX for Focus sport

[J N Hiller]

Aha! Interesting. I wasn't aware that there were two different carb's used
on this engine. What numbers are on each carb? My engine is most likely
later production and it runs fine in the Venus 2 with the tank on the
firewall with reasonable prop sizes.

John Pavlick

J N Hiller <jnhiller at earthlink.net> wrote:

	Bob, I am getting back into this discussion late. I went to the bearing
store and when I got home it was miller time.

	John they were labeled the same, which is what prompted me to inquire to
"Engine Support" as whether there was a change and which one was "correct".
I still have the e-mail chain with the standard reply to send it in and no
answer as to which one was correct. I made mine work and dropped the issue.
I guess I should have inquired directly to OS but not being their customer
my inquiry would likely be disregarded.

	Jim



	-----Original Message-----
	From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of John Pavlick
	Sent: Friday, June 27, 2008 6:33 AM
	To: General pattern discussion
	Subject: Re: [NSRCA-discussion] OS 91FX or 120 AX for Focus sport





	I have two AX'es purchased at different times and their carburetors are
different (see photo). I am currently using the OS muffler and the first
motor carb pictured on the left has a serious fuel draw problem and the
other one works fine with the tank against the firewall. I was already into
a 1.20 size airplane when the OS 1.20 AX appeared on the market and I got
one right away, which was likely early production (left carb). The idle
needle didn't withdraw fully from the fuel delivery tube at full throttle
and the barrel has an air bleed hole through the bottom side, which opens to
the intake around half throttle. I shortened the needle, which helped some
but ultimately I added an exhaust restrictor (.350 ID) to increase
backpressure before I got an acceptable mixture setting and transition.

	I inquired about the difference but understandably got no reply. The other
carb from the second motor works much better.

	I suspect running a 16-10 is a little too much load and I need to advance
the throttle before going vertical to get the RPM's up to produce sufficient
back pressure / heat or it will go lean. The OS muffler is likely sized to
operate with more exhaust volume using a smaller prop at higher RPM's.

	I plan to try a double quiet Mac pipe, probably with a pump in the next
airplane.

	Sorry about the photo size. I had to make it quite small to fit the file
size restriction.

	Jim Hiller

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