Navion pilot reported loss of throttle control on takeoff. Pilot returned to departure airport and after landing found the throttle cable linkage was disconnected.

Narrative

After stopping at ZZZ for fuel; I performed a routine sump of the fuel tanks and normal runup of the aircraft; then approximately XA:30 I was cleared for takeoff on course to ZZZ1 from Runway XX. Takeoff roll was normal; all systems on the green; rotated at 65mph; gear was retracted upon positive rate of climb; once I reached 700'MSL I pulled the propeller back to 2500RPM; suddenly at about 1000' I noticed a reduction of fuel pressure from 25gl/hr to 5gl/hr; I immediately pushed all knobs in; mixture; props; throttle. Checked and made sure the fuel lever was on the main fuel tank position; then turned the boost pump on high pressure; checked rate of fuel stayed the same; switched to low pressure with the same result; no change. I kept the aircraft climbing to give me more options in case of an off-field landing; the aircraft began to lose speed. At this point; I kept the airport in sight to my left; I called ZZZ Tower and [requested priority handling] saying I was returning to the airport due to fuel problems. The controller directed me to land straight in on Runway XY. While descending to land on Runway XY; I was too close and too high for a normal landing even after forward slipping the aircraft so I requested to perform a 360; which Tower clear me for a right 360 turn. Once I was lined up on final for Runway XY and retarded the throttle; I noticed no change in the power output; I realized the throttle cable was inoperative. I was too close and too fast to land on Runway XY; I requested a change of runway; ATC told me Runway XX was available. I turned right; cutoff the engine power and landed without incident. ATC told me to stay with the aircraft and they would send operations personnel to help. I performed an engine restart and contacted ATC and said I would taxi to the ramp. At the ramp; I met with two operations people; I gave them my name and phone number. Shortly thereafter; I received a phone call from the ZZZ Tower manager; Person A. We discussed the events leading to the [priority] landing; he then informed me that ZZZ Approach said to him that I was identified as a target of interest for flying into their Class C airspace (1200 feet). Person A said he would communicate the [priority] landing situation to ZZZ Approach. After the phone conversation with Person A; I looked under the instrument panel; everything seemed normal; all cables attached and in place. I proceeded to inspect the engine compartment for any obvious abnormalities. The fuel lines were all connected and normal. I noticed the throttle cable linkage had become disconnected. I found a bolt; a spacer; a washer and a castle nut inside at the bottom of the cowling. The cotter pin was missing. I went to the aircraft maintenance shop on the field and the A&P mechanic gave me a new cotter pin. I connected the throttle linkage; tested the connection; everything worked normal. The flight to ZZZ1 was normal and uneventful. This event has made me more aware of the subtle issues that can come up; this issue could have been caught during a thorough preflight inspection. Upon reflection of this situation; the throttle linkage is hidden from view during inspection while the throttle is pulled in the idle position but in full view when the throttle is in the open position.As for the potential airspace violation; just the thought of fuel contamination and being low to the ground was my main concern. I should've contacted ZZZ Approach in addition to ZZZ Tower.