YS 91ac lost compression
 

compression on this engine has gone to pot. I dont know what to do with it? The engine runs pretty good it is just missing the kick that it had before. I checked th valve clearances and it is just as factory describes. I have always run this thing slobbering rich as I do all my 4 strokes.

What should I check first? I have a complete gasket set so taking it apart is no big deal for me.

SO any YS fans out there that can give me some pointers?

Thanks in advance guys. -BT

RE: YS 91ac lost compression
 

Hi BT, you didnt say how much runtime you have on this engine?
Do you fly off a grass field and maybe over time the carb has sucked up specks of debris and some dirt, causing the compression to get lower over time. If you have lots of runtime on this engine, maybe a new piston ring is in order? You may also want to check out the YS engine section here on RCU, Troy Newman is the moderator there and he is the GURU and a great guy too for asking advice.
Keep us posted on what you find

RE: YS 91ac lost compression
 

If you are running your YS engine "slobbering rich", you probably glazed the cylinder wall
and lost the ring seal....resulting in the loss of compression. If indeed that is the case, you
may have to re-ring the engine, and de-glaze the cylinder wall.

FBD.

RE: YS 91ac lost compression
 

Running any 4 stroke that rich isn't good unless the break in procedure calls for it. You are also losing a lot of potential power. and blowing good glow fuel out the exhaust instead of burning it.

Since you are looking for the first thing to do, tune the engine and see how it runs.