[NSRCA-discussion] YS engine follow up

[Michael Cohen]

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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