YS 120 NC Idle & Regulator Screw Exist?
 

Hi Dave- I've a new YS 120 NC that's run perfectly for first 15-20 flights. Now some low end adjustment is necessary since its getting run-in. Idle is too rich & I need to lean. Does this engine have a low speed idle screw? Where is it? Or do I adjust the pump regulator screw to adjust idle. If so, then won't this affect my high end adjustment?

As a side note- my roundish muffler with this engine was constructed of 2 halves welded together with a low temp metal filler (I think)... anyway, after 20 flights the metal filler has melted & my muffler is coming apart. Is this why I don't see any of these around any more? It worked great before it melted!

Thanks for your help!

RE: YS 120 NC Idle & Regulator Screw Exist?
 

The NC does not have an idle airbleed. The airbleed hole in the carb barrel may have to be drilled out slightly to make the idle lean enough. We usually open them to 1/8th inch. Mufflers for these can be an issue. Check with YS Parts at 775-782-4562 for a replacement.

RE: YS 120 NC Idle & Regulator Screw Exist?
 

Dave- I disassembled the barrel & found 3 holes. I believe hole "B" is the air bleed hole you're referring to, am I correct? If so, this hole is less than 1/16" in diameter and I'm a little reluctant to double the size to 1/8". I'm thinking I'll start with 5/64" or 3/32" & check performance. Sound like a good plan?

RE: YS 120 NC Idle & Regulator Screw Exist?
 

B is the right one. Opening it up a little at a time is fine. Just let me know where it's finally correct, OK?

RE: YS 120 NC Idle & Regulator Screw Exist?
 

I drilled out the air bleed hole with the smallest increment drill bit I had... 5/64". Reassembled and started the engine. Wide open throttle & midrange were still excellent. When I went to idle, I'd guess 2000 rpm with 15x10 APC prop, the engine would sag a couple seconds & then speed up a couple hundred rpm (might be the tiniest bit lean?) but then idle for as long as I cared to.... :D:D:D Additional tests confirmed results & gave me confidence in our fix.

Case closed! Just ordered a case of fuel... [8D]

Thanks Dave!

RE: YS 120 NC Idle & Regulator Screw Exist?
 

Good! You might be able to correct the small problem at idle by slightly richening the regulator.

Good Flying!