Inverted installation affect idle?
 

I have a YS FZ91 that I have mounted inverted on my Decathlon that I have never been able to get running just right. Is their anything special that you need to do when you have an inverted installation? I've seen pics of the pattern planes that use YS. Do they use an on-board glow on those things? I would rather not add the weight but if thats what it takes I'll do it.

The problem is getting the idle down to 2000 rpm without shaking and dying out. It runs much smoother at a higher idle rpm but still seems to die out eventually. Regulator is set flush. Transition to full throttle is smooth. Top end is easy to set. It seems to end up at about 1 & 1/4 out when I get it where I want it. I start out with an Idle setting of 2 & 1/2 out but have to turn in a little because it speeds up a little and dies out after I bring it back to idle. When I richen the low end to the point where its not speeding up after I bring it back, it Idles great for a while but still eventually dies out. I'm doing this at about 2500 rpms though because it shakes and doesn't want to run smooth when I try to get it down to 2000. When I let it run a half throttle, It seems to run pretty smooth, but when I bring the power back to idle from there it seem to die out much quicker. Valve clearances have been checked and the engine is being run static without a cowl.

I've been using a light prop (Zinger Pro 15x8) because the nose is a little heavy. Is a heavier prop recommended with this engine to help it idle? Should I reduce the fuel pressure with the regulator a little, reset the other two adjustments and try again? How critical is it to get the idle down to 2000 anyway? could it be just because it's mounted inverted?

When it dies, quite a bit of fuel drips out of the carb and drips onto the ground. I don't think it would keep coming out until the tank lost its pressure though.

This is my first YS (I've got an FZ120 still sitting in the box though) so all of this is pretty frustrating. Any ideas?

Inverted installation affect idle?
 

99% of pattern airplanes use inverted installations and those guys have little if any problem.
The reg screw probably needs to go out. Start with 1/2 turn and see if the problem improves. You may also have to close the air bleed. Try going back to 1.5 turns open as a start.
ONCE AGAIN, THE REGULATOR DOES NOT CHANGE THE FUEL PRESSURE!!!!!!!!!!!!!! IT is a demand type regulator which you adjust to give the engine more or less fuel, DEPENDING ON THE THROTTLE POSITION!!!!!!!!!!!!! Think of it as a mid range needle.

You did not mention plug or fuel, what kind? The prop should not make any difference.

Inverted installation affect idle?
 

I had an OS F plug in their but I just changed it out with a YS Four stroke plug. The element in the OS plug looked a little white. I also run PowerMaster 20/20. I'll tweak the regulator until the midrange is right on, then readjust the top end and then readjust the low end. Does that sound like the right order? I think I'm pretty close. Hopefully that will do the trick. I also bought an APC prop and reset the valve clearances.

Inverted installation affect idle?
 

Here's the way we do it.

Start the engine at about 1/4 throttle and allow it to run for a minute or so.

Slowly come up to full throttle and work the hs needle in until it's about 2 or 300 rich side of peak. Let it run for a minute or so.

Reduce throttle to idle of about 2200 to 2400 rpm. Leave it at idle to see which way it goes. Gradual increase in rpm indicates lean, if it does this, richen regulator and possibly richen air bleed.
If too rich at idle make opposite changes.

When it 's about right, check transition from low to high. Adjust regulator for good transition.

BEFORE DOING THIS, CHECK THE VALVE CLEARANCE WITH ENGINE COLD. SHOULD BE .003", BOTH VALVES.

Inverted installation affect idle?
 

I don't think I'm getting anything when I adjust the regulator. I didn't do the adjustments exactly the way you just described though. First I adjusted the valves, but I adjusted them to be between .04mm and .1mm. .04mm was a close fit so I know they were closer to that. Then, with the regulator flush, I started it up and set the top end a tad on the rich side where I could hear that the rpms were just a little less (too cloudy this morning for the GloBee), then I checked the transition from idle to max. It accelerated very smoothly and rapidly. Then I checked the idle mixture by running it at full throttle and bringing the power back to idle fairly quick but smoothly. I then listened and it would slowly speed up and try to die so I richened the low end adjustment. I did this a few times until it idle well. After those adjustments I checked the acceleration again and its still good. Then I power up to the mid power setting to see how smooth and steady it runs in the middle of the power band and thats where it gurgles a little. And when I bring it back to idle after it gets running like this it dies out. I acts like its loading up when its left to run at about half throttle. I tried to adjust the regulator while its running at this power setting to see if I could lean it out a little (you said to think of the regulator as a mid range needle) but nothing would happen. I could turn the regulator a full turn in either direction with no change in the way it was running at half throttle. Could this be the problem or is adjusting the regulator at this point totally wrong.

I won't be able to get back to it for a couple of days, but I'll try to make the low end mixture adjustment with the regulator like you described next time and see if that does anything. I have tried to set the idle with the regulator in the past with no success but I'll try it again. I think I am getting a better feel for it now so maybe this time I'll get it. I'll let you know how it works out.

Thanks