Originally Posted by
bjr_93tz
10 thou would make life easy for the cdi unit..
Something I've realised in the last few weeks is that my valve clearances have been bordering on too tight for the 7 years I've been running it. Just prior to swapping to the 19x11, I cleaned the plane up, reduced the valve clearance a bit then put it away. The very next flight at the field (same prop, same fuel) it started a very small misfire about 4 minutes in that got worse but was still flyable. I reached for the screw driver to lean the regulator, but stopped, remembered what I'd changed from last flight then opened up the clearance again and it was back running without fault again.
For whatever reason, my engine is not happy with less than 0.05mm (0.002") valve clearance at TDC. The clearance on the exhaust side is all over the place and even with 0.05mm at TDC it gets tight at other points. I wonder if the cam grind is/was a bit iffy?
I'd read on the 'net about people running 20% oil without problems, something my engine has never run happily on. I'd seen the videos where on takeoff and different times you could see the individual puffs of smoke in the exhaust trail and wondered how they could run so rich because my engine could never be set like that and run properly. Even for the couple of years when it was "reliable" I had to have it set super lean (needle and regulator) to prevent misfiring, so lean that the high speed needle was often on the lean side of peak rpm. Being my first YS and no other YS's (cdi or otherwise) around my area I figured that's just how it was.
What a difference this engine is to run now.
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Sounds like you're starting to get a handle on it Brett. The cdi's are a different beast to run and tune. YS have changed the clearance settings over the years. Used to be a minimum of 2 thou, now for the 185 they say zero to 4 thou. I use a 1 1/2 thou feeler guage and set it so there is a slight amount of resistance as it slides through. I think setting to zero is asking for trouble.
I've seen different percentages of oil run up to 20% with no issues. I've run various brews from 9 -15 with mixture settings being the only change required. Now you have it running well, I think you will be to use less oil OK. Because it was so lean, I reckon it needed the extra oil to keep it cool enough. It does sound like over heating was the cause of the poor running, but there were other problems that was causing the over heating. If that makes sense.
Fly the pants off it now
