[NSRCA-discussion] YS engine follow up

Fri Aug 21 12:47:21 AKDT 2009

Make sure you pinch the line when it is running full throttle.  If the
rpms jump, your needle is too rich.  If you pinch it and they stay the
same, you can back off two clicks.  If you pinch the line and it cuts or
drops in rpms, you are too lean.

Thanks,

Jim

From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Michael
Cohen
Sent: Friday, August 21, 2009 4:46 PM
To: nsrca-discussion at lists.nsrca.org
Subject: Re: [NSRCA-discussion] YS engine follow up

I will check that as well at the field on Sunday, but it was idling
really well for about 20 to 30 seconds.

________________________________

Date: Fri, 21 Aug 2009 14:58:08 -0400
From: jim.woodward at baesystems.com
To: nsrca-discussion at lists.nsrca.org
Subject: Re: [NSRCA-discussion] YS engine follow up

Hi Mike - did you "pinch" the fuel line to see what the rpms would do?

Jim

From: nsrca-discussion-bounces at lists.nsrca.org
[mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Michael
Cohen
Sent: Friday, August 21, 2009 2:52 PM
To: nsrca-discussion at lists.nsrca.org
Subject: [NSRCA-discussion] YS engine follow up

Well, I ran the YS engine I had trouble with the other day and am
reporting back with my findings.  First, the inspection and changes.  I
looked for cracks or splits in the o-rings and saw none.  I went back to
flush on the pump (it was about 3/4 of a turn out).  After starting the
engine and running on a high mid throttle and back down to idle, I
tweaked the pump slightly to keep a good 2000 to 2200 idle.  I left the
high speed set where it was, but after running at full power, I went to
get the tach and the engine would die abruptly.  I decided to check the
valve clearance and reset it to .0015 to .0020 inches.  Since the valve
cover was off, I did a quick wet sand on the valve cover.  Since I was
out 2.25 turn on the main needle (much further than any other DZ I
have), I decided to simply turn it in to 1.75 turns and see what would
happen.  I know for a good controlled experiment, one should not alter
more than one thing at a time, but the engine seemed to work just fine
now.  High end power was up to 7400 to 7500 RPM on an 18.1 X 10 prop
from the 7200 (but rapidly sagging) setting before.  Richening the high
setting slightly cause a slight drop in RPM, so I left it at 1.75 out
and double checked the idle and the transition from idle to full power.
Everything seems to work great, but I will try it in the air on Sunday
before feeling more comfortable.

In summary, from the previous, issue free running of this engine in a
Brio, I made the following changes:

1)  Had a mid air and buried the engine nicely in a plowed field.
2)  Disassembled, inspected, cleaned, and reassembled the engine (using
klotz synthetic oil as a lube) and installed it into an Eclipse
3)  Used a 18.1 X 10 2 blade in place of the 15.5 X 12 4 blade
4)  Ran the engine on the ground to check its operation, all seemed
normal
5)  Had one flight on the engine last weekend and on the second flight,
the dying at full power issue popped up.  Admittedly, it was a very
humid day last weekend.
6)  Reset the pump to flush and checked the idle for a nice 2000-2200
run.  The high power setting issue was still present.
7)  Reset valve clearance, sanded the valve cover, and reset the high
speed needle to 1.75 turns out.  Problem solved!

So, now for the educational questions:

Could the high speed needle being so far out have cause the abrupt high
speed "flame out"?

Does switching from a 2 blade from a 4 blade make a difference and why?

Does the valve clearance being in the .003 range instead of the .000 to
.002 (as recommended) make that much of a difference?

Could an air leak cause this high speed flame out problem?

I am interested to know so I can someday become the Troy Newman of the
East (maybe) for YS engines.  I don't get a heck of a lot of flights per
year, so my statistical database is lacking.  But that said, I did help
two people with their YS engine troubles at the Weak Signals contest so
I must be learning something!  Thanks all for the help.

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