Yes, your main jet is in there and is not adjustable. I've never seen one with a bolt like that in the hole though. Usually it it screws in all the way to the head like this .



An adjustable jet


"It's just a phase. He'll grow out of it." Mama, 1964

1956 Chevy 1/2-ton 3100
1953 Chevy 6100 "The Yard dog"
1954 GMC Suburban Now with a new proud owner.