I have a used 120 that I want to put in my edge,  this is my frist OS120 engine , there is no pump but there is a pressure fitting in the rear what is this for ?

as i recall that fitting was to vent and drain old oil and combusted acids from the crank case - common in 4 strokes.....put a piece of tubing on it long enough to stick out from under the cowl. After a days flying, you can use that tubing to put after run oil into the crank case to prevent corrosion...run the engine dry, then squirt aro into the tubing

Now that's as I recall. Others may well have other opinions and suggestions - feel free to jump in..

Fingers is bang on. There is a fitting on the muffler of the old 120 for tank pressure.

Thank you , I seem to have an issue tho , will not start , seem to be low on compression ,

I checked the plug , made sure the pitson is moving ....  ,, 

I need some pointers on this to debug,   2 strokes I am good at  fixing

should I pull the valve caps make sure   vavles are opening ect ....

Paul
First thing is to remove the valve cover's and give her a spin by hand to make sure the pushrods and valves are moving. If you've got low compression on a 4 stroke that's been sitting a little while 99 % of the time it's a stuck valve.

Yip, that's what it was ,   stuck intake ,   now I seem to be missing one lock nut on the tappet,  anyone know what size  nut this would be ,  I have checked the exploded view and it does not say

Update , i found my nuts .....    lol,    it was stuck to the side of lifter / valve

had a good friend and flyer visit last evening and adjust the  clearances for me , we now have good compression ......  ::)

Betcha she'll run now  :)