The chain lubricator not feeding

not on the older chainsaws
newer ones it s normally the black lever you hold
Check the Chain Brake
Make sure the chain brake is working properly by putting the chainsaw on a stable surface. Release the chain brake, squeeze the throttle and then activate the chain brake by pushing your left wrist against the kick back protection without releasing the handle. This should cause the chain to stop rotating immediately.
source
http://www.tractorsupply.com/know-how_home-garden_outdoor-power-equipment_chainsaws_the-basics-of-using-a-chainsaw-for-beginners


can be part of the centrifical clutches

depending on the make and model there should be a nut , sited close to the motor , close to the bottom cog. When you undo that the chain carrier should also be removeable. Remove the chain and refit the new one and fill the lubrication point. Reassemble keeping tension in the new chain.
There should be videos on youtube showing the procedure. It is fairly straightforward but there varying designs/layouts

That's an unusual problem, usually the opposite happens. After making sure the chain brake is off, loosen the two nuts that hold the bar. Be sure to hold the bar up when adjusting the tensioner screw and adjust until the chain is just snug, but not too tight. While still holding the bar up, tighten the two nuts firmly. Check to see that the chain can move freely by hand. Then start the saw and run the chain at speed with something in front of the nose to check for adequate lubrication. You should note a slight fine spray of oil on the object in front of the nose of the bar. Inadequate lubrication, a chain that is binding on the bar, or an overly tight chain can cause the bar to heat up and expand, further tightening the chain. A properly adjusted Stihl saw will use almost all of the chain oil in the reservoir for every tank of gas. Too much oil is better than too little. The oil feed may have to be adjusted for operating in temperature extremes. If operating in very hot conditions, be sure that the saw has not run out of chain oil. The oil feeds faster when hot.

Did you take teh Chain off and the Bar and see if the Oil Feed holes are clear of sawdust?

You are free to charge to the top if you think right to use a chainsaw. It is essential that the oil is clean. If you accidentally charge too much (full hopper) it is good the rest of oil put back in the oil bottle or to extend on the chain. It is important that it is not oil-free and should be cleaned around the chain for good lubrication.

turn the nut counter clockwise so that it backs out a bit this tightens the cable to clutch

Make sure the chain is not too loose it should sag aboug 1 eight of an inch. If the chain is still slipping than you have to replace the centrifical clutch.

HI , FIRST UNDO BOTH SIDE COVER BOLTS ON THE CHAIN COVER AFTER MAKING SURE THE CHAINBRAKE IS IN THE OFF POSITION,[BRAKE LEVER PULLED BACK].TAKE THE TWO NUTS OFF REMOVE THE COVER,LIFT THE BAR SLIGHTLY AND PUSH IT TO THE REAR.THAT WILL LOOSEN THE CHAIN SLIP THE CHAIN OFF THE BAR AND REMOVE THE BAR ,ONCE THE BAR IS OUT OF THE WAY ,YOU TAKE THE CHAIN OFF THE SPROCKET BEHIND THE CENTRIFICAL CLUTCH AND SLIP IT OUT AROUND THE BACK. AFTER CLEANING EVERY THING ,PUT IT ALL BACK THE SAME WAY .YOU WILL HAVE TO SCREW THE ADJUSTER BACKIN SO AS TO EASILY FIT THE BAR TO THE ADJUSTER PIN ,IT IS NOT DIFFICULT AND AS YOU SEE THE PARTS IT WILL FALL INTO PLACE

your centrifical clutch need to be replaced there is no adjustment,I hope this helps you?

It sounds like the centrifical clutch is in need of service or replacement, or the brake is not adjusted properly.