On the XL model series units the oiler is actuated by way of crankcase pressure. You will have a fitting on the crankcase (in the vicinity of the carburetor) which in turn goes to the oil reservoir and pressurizes the tank. There is a small duckbill valve pressed into the tank that allows air pressure in but not out. This pressure feeds oil to the bar. There are two rubber lines involved to move the air from the engine and oil to the bar. This is a very lousy set-up and is notorious for failure. Areas to check are: duckbill valve, oil tank cap (if it leaks it won't seal and not pressurize the tank), supply and feed lines colapsed/plugged or in a worst case a leakage of the intake system whereas it can't possibly create the needed pressure due to crankcase leakage (seal(s), gasket(s), etc. related to the crankcase).
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