I have been trying to tune my os 37 for a long time now. It keeps losing power like I can't keep it up high because after awhile it will fall from slow to fast power lose. I have tried tuning leaning in and out both high and low niddle. I also checked fuel lines and tank. It seems to me to be running lean but sometimes when I go to move it alot of fuel poors out of the muffler. So I leaned it out a good few times and tryed riching it up trying everything for weeks now and can't get it to run right. I also noticed lately it has had like darker fuel coming out of muffler like greenish brown latest was black whats that mean? I need help please any ideas? I think my engine maybe finally broke in since not that old so can see why I might need to tune but tryed everything on needled many time please help.

Sounds too lean. Heli engines when rich will power slim out the exhaust. Even when tuned correctly will spew oil out.
Flying for a while then slowly loosing power is a symptom of overheating and overheating is a symptom a lean mix.
Heli engines run richer than airplane engines.

Have you checked the temp? Use a temp gun or the old finger on the back plate trick. 185 or so with a temp gun or about 3 seconds with your finger on the back plate before you can't stand it is a good starting point. I think you're way lean, getting hot and losing power and black stuff out the pipe. You should have some good smoke coming out and it's normal to see fuel (oil) spiting out the pipe. Remember your engine only burns the alc. and nitro, the caster or blend of oil which is 18% of your fuel doesn't burn, it only lubircates and comes out the pipe. An oily mess is normal for a nitro engine.

I would suggest going back to factory settings and working your way down. I have an OS 37 and have had great success from day 1.

What pipe are you using?
Have you changed the glow plug since break-in?

I have tried leing in it out and riching alot back and forth I guess I didn't really riching it alot because I was watching smoke and plenty way to much smoke was coming out or so I thought. I also could smell the nitro alot more so thought it was rich. But I didn't change glow plug since it broke in if it did maybe I will try that. I also will try factory settings maybe. I am using the stock muffler that came with the hawk pro black one.

Well I tryed a new glow plug and no luck I even went back to factory settings or I think I did. Because I am not exactly sure what 3 turns means if that means like all the way around is one or what. But I tryed both and then I messed with it forever and still no luck. Any more idea's please help? I have already opened up tank and checked lines any ideas?

Yes, 3 turns means 3 times all the way around from fully closed. Do you have the vent line connected to the muffler? Are you sure the fuel is not contaminated? If it runs fine when first started but then loses power after it warms up then it would be lean. Can you touch the backplate after you land?

Yea the vent line is hooked up to the muffler just not sure if it is aiming up like it should. I was when I put it in but I have a tendendsy to mess with things and make sure it si right and I may have moved it. But sometimes I can touch the back plate sometimes I can't depends on my tuning but I have tryed tunning and tunning and tunning. But the fuel maybe old plus I mixed two fuels but only after it was running this way anyway. But my fuel maybe have stuff in it I can see grass or something in the bottom of fuel but I have a filter on pump I think so didn't think that would matter.

Get new fuel. Fuel can have nothing in it and you have to keep it sealed shut because it's hydroscopic, it will absorbe water out of the air. Also it gets stale with age.