I power voltage regulator by 12V / 8A power supply. 

UA78S09 is responsible to convert voltage to 9V for DC motor, which is able to swallow 1,5A at start and under heavy load. Motor however does not start even if specs for regulator states that it should be capable to provide 2A current. 

Multimeter shows proper voltage 9V but max current peaks on around 0,4A only (only multimeter - no motor connected).

Why is that so?
 BTW: I have attached heat sink to regulator (if it matters here) and do not use capacitors.

Disclaimer: I am total noob, just started playing with simple circuits. So please be gentle with me ;-)