Lior,
Could very well be some oil residue that has solidified. Pull off the front cover, pull off the lube line from the nipple and inject some kero directly down the lube line into the engine. Turn the shaft over with some compressed air and repeat a second time, then reassemble. During the first run, let the engine idle for a few min (dont go to full power!) then shut down and see if they smoothed out. If not... probably need to be replaced....