Wphew.. How quickly the point of the original post goes awry.

WD40, Marvel Mystery Oil, fuel, whatever works.

As for me, I soaked an old engine, a somewhat vintage OS 61 SF that I bought at an estate sale, in a coffee can that I filled with ordinary glow fuel, high enough to cover the engine, and let it sit for a week. After that, I cleaned everything out, mounted it, and started it up. It ran just fine. Originally, the throttle would not move hardly at all. After the soaking, it moved like a new engine. Do what ever you need to do to free the carb using any method. I liked my method because it exposes the engine to exactly what makes it run and it both dissolved the old crud and lubricated, heck it contains 20% oil blend, so why not.

But let me offer this one point. Hoss said it, but there may need more said here. I would disconnect the linkage and see how the throttle works. If it's gummed up, well, read the above. If it is NOT, then there is something going on with the servo or linkage or both.

I have offered this method to several people in the past, but here it is again.

1. Make sure your throttle channel does not have any expo, end points, or anything like that - meaning that it has full movement end to end, then, using your transmitter with all trim removed, electrically center the servo. This means put your throttle stick on the transmitter in the center, as close as you can get it visually.
2. Mount the servo in the proper servo slot in your fuselage.
3. Put a servo arm on making sure you select one of the arms that will be perpendicular to the side of the servo that is in parallel with the throttle on the engine. The splines in the servo shaft and inside the servo will pemit rotating it to find the one position that provides a good perpendicular mounting.
4. Center the throttle on the engine.
5. Connect the linkage shaft being careful not to move either the servo arm nor the throttle. I would suggest a Z bend on the servo and a plastic clevis on the throttle. Twist the clevis so that you have plenty of adjustment room, both in and out, in the threads This will prevent any metal-on-metal friction that can often cause electrical interference due to vibration. Using the clevis, adjust it so that both the throttle and the servo arm are both centered. One point here. I would choose a center hole in both the throttle arm and the servo arm. This will give you room for mechanical adjustments that will surely happen. Re-check centering. If it all looks good, then continue.
6. With both ends of the linkage connected, SLOWLY move the throttle stick to full open then to full closed. No doubt, there will be either to much movement or to little. The goal here is to have the throttle fully open when the stick just reaches full travel. No more no less. Any less and, well, you won't get full throttle. Any more and you will bind up the servo and either break a tooth in the servo spline, drain your battery, or both. A small point here. I use a gadget called Voltwatch2. It can be plugged either into an empty receiver slot or, using a Y cable, into any of the used slots. This will give you an outstanding indication if you are having throttle binds.
7. Adjust the linkage at the clevis to the point where full open has the throttle fully open - again with no binds, but with the idle end, adjust your trim so that it is fully closed then pull the throttle to fully closed position. Re-check the fully open again because the trim will affect both ends of movement.
8. You can move the throttle linkage to any pair of holes in the arms as necessary, but watch out. You can lose resolution if you are not careful. Spend some time on this.
9. Repeat as necessary until you are satisfied with the way the throttle works.

I admit that this could be a long process, but if done right, you will have a smooth operating throttle from idle to full open with room on the idle side to operate a cut-off button or switch, on your transmitter and you will have absolutely no binds in the linkage.

Good luck.

CGr.