Vans RV7: Throttle/mixture back out on startup; GTN750 and GFC500 won't power on

Hi Chris,

That combo (throttle/mixture “backing out” + only some avionics powering) usually points to either (a) hardware axes/switches constantly overriding the cockpit, or (b) an electrical/avionics power split in the RV-7 panel where the GTN/AP are on a different bus/switch than the one you’re toggling.

1) First check for axis “fighting” (most common)
Even a slightly noisy throttle/mixture axis will snap the in-sim levers back to wherever your physical controls are sitting.

Do this test:

1. Load the RV-7 on the runway (so the engine is already running and you’re not dealing with startup logic).
2. With the mouse, move the mixture and throttle in the cockpit and watch them for 10–15 seconds.
3. If they creep or snap back on their own, that’s an input override.

Quick fixes to try:

1. In MSFS Controls, search your devices for Throttle Axis and Mixture Axis. Make sure you don’t have them bound on more than one device/profile (yoke and throttle quadrant and gamepad, etc.).
2. Temporarily unplug/disable any extra controllers (gamepad, spare joystick, etc.) and re-test.
3. If your hardware has mixture/throttle levers, physically set them where you want them before touching the in-sim levers (to see if they’ll then “agree”).

2) Check for an avionics/bus switch specific to the GTN/AP
Since your G3X/G5 come up but the GTN750 and GFC500 don’t, it sounds like they may not be on the same avionics feed in this particular RV-7. Some panels have an additional “GPS/NAV”, “COM/NAV”, “AP”, “Essential/Avionics bus” or similar switch/breaker separate from the general avionics switch.

What I’d do in the cockpit:

1. Look for any additional avionics-related switches (to the left side panel, center stack area, or circuit breaker row if modeled).
2. Check for any popped breakers related to “GPS”, “NAV”, “AP”, “AVIONICS BUS”, etc. (if the addon models them).
3. Try turning on the battery, then alternator, then avionics, then any secondary avionics/bus switch (in that order).

3) One more easy isolation step
Try spawning with a “Cold & Dark” state (not a runway start) and do a manual power-up. Sometimes a saved panel/state causes certain components to stay unpowered even though other glass displays come alive.

A few quick questions so I can narrow it down:

1. Which exact RV-7 addon is this (developer/store)? There are a couple RV-7s out there and they don’t all wire the same.
2. Are you using any external hardware for mixture/throttle (and if so, which brand/model)?
3. Does the GTN750/GFC500 ever power on if you start on the runway (engine already running), or is it dead in all start states?
4. Any other avionics mods running (Working Title stuff is fine, but anything else that touches GPS/AP)?