HI, cbdeitz here...We have a Troy-Bilt, z-start, 6.75 HP, 21 inch self-propelled mower, about 4-5 years old. This belonged to my dad who has recently passed away & we can't find where the air filter is located. Mower starts right up but won't keep running. New gas, new oil, clean, new spark plug...Help, I'm a female & am 72 & every mower I've ever had it has been easy to find & clean or replace the air filter, but can't seem to find any air filter on this mower. No prime & it appears no choke either. Thanks for any help.