I was at the track yesterday and after 6-7 laps having the engine(H8P) slightly rich it suddenly leaned out on it's own.
Why did this happen?Was it an air leak or something?
And i also noticed that my runtimes are a shorter than most in here.I run about 6-7mins and can't lean it more cause of high temps!

Sounds to me like you are running 15% nitro and say 15% oil ? What kind of pipe are you running ? is it the standard Hyper 2 piece pipe and header with a rubber joiner ? If so the Fuel could be the reason you are getting bad run time.. and the leaning could be an air leak in your pressure line or the rubber joiner from header to pipe...

let me know ..

I run 20%nitro and 13%oil with SH #5 glow plug on stock pipe.I can't zip more on the rubber joint.I removed one shim a week ago from the head to see if i can make it run at lower temps with a richer mixure but that's it.

Put the shim back, The laening is all part of the break in of the engine as it wears.

How hot are you running on average? Seal your carb neck, back plate, and HSN with o2 sensor safe high temp RTV, put that shim back in, and give it another go. My Hyper 8 port was leaking at the carb neck and it was a pain in the ass to tune and it was running hot until I sealed everything.

I did put the shim back on, i just removed it to see if there is any difference.
I do have air leaks...when i finish my runs there is dust+fuel on the neck and screws of the carb and there is some under the cooling head.
I removed everything last night and used PTFE to seal them and silicone on the neck,head and pull start plate.
I didn't do this sooner because i thought that there wasn't much of a leak to increase the temps at ~280 and not let the engine run any richer,i thought the problem was somewhere else.
Did anyone noticed any difference in temps and tuning after sealing everything and how much?
Also, when i removed the pull starter and tried to put it back,the only way to fit it was to let some rope out about 1.5inches.To fix this i have to cut the rope and tie it up again closer to the plate,BUT i can't remove that steel cylinder on the handle of the pull starter that the rope pass around it.How can i pass it through there and tie it up?