Help. I’m putting an older OS 48 Surpass on my plane. Because the throttle is on the rear of the engine that puts it about 1 inch from the fire wall. And because the throttle arm pivots around the throttle screw the hole to mount my push rod to is never on the same plane as my push rod and it’s binding. What to do?
I hope I’m explaining this right. I need to get this in the air tonight.

Use a pushrod that has some flexibility, e.g. small diameter wire; then make it long enough to extend beyond the throttle arm and bend it back (so it looks like the slide of a trombone) and attach it to the pushrod from the front of the engine. I'ts easy and usually works well.

DaveB

Same trick works well when steering arm tiller is too close to the firewall.

On 4-stroke engines like that what you need to do is bring the pushrod out of the firewall PAST the throttle arm and then put a U-bend in the pushrod, and bring it back to the control arm. See attached diagram. This is actually a pretty common thing to deal with on 4-strokes.

Ken

I just switch over to 4 strokes and had the hardest time getting the throttle set up. I use a flexible braided cable and sometimes the Dubro 4s throttle linkage. Makes a very smooth setup.
The loop way RCKen described will work fine . I use large fiberglass mounts that have a big webbing on them and have trouble getting the wire to clear.

I had the same problem with my RV-4, so a combination of what the others suggested and make the exit from the firewall more of a vertical slot - instead of just an exit hole. (Exaggerated for clarity in pic)

The looped back wire usually works ok, but sometimes the wire flexes and you can't get the throttle to close all way, or it's not very smooth. It's easy to make a bellcrank system using and extra servo arm. Simply screw and arm (or wheel) to the front of the motor mount, on the side with the throttle. You can tap and thread or use a small sheet metal screw. Don't tighten so far that the servo arm doesn'e move. Epoxy on the screw will keep it in. Run the throttle rod to a hole in the bottom of the arm and another from the top of the arm to the carb throttle arm then check the direction of travel and adjust accordingly.

Flying Greg beat me to the explanation while I was making this drawing. Bell Cranks work great in this situation.

Brad

Good drawing BKDavy. Thanks.

Thats what I ended up doing. Nice drawing. Tx

Or you can do something like I did on my Hog Bipe.

The throtle actually pulls up and down, and the bell crank lowwer pushes back to front.

That needle must be fun to get at.

drill a big enough hole in the firewall to allow for the rod movement. run a straight 2/56 rod back to a servo with no bends, kinks etc. This may require moving some things around,. but it will provide a slop free smooth linkage that will never let you down. Nyrods expand and contract with heat and are poor choice for precise throttle control. Anything like bell cranks etc adds slop and is more complex then it needs to be. I set this up during my planing stages so the gas tank, servos etc are in the right place. A retrofit may not work without some compromises.

How do you draw, post such a sketch? I am a computer dummy with windows xp home and paint. Thanks.

The drawing is post #4 was done by MinnFlyer who is a graphic artist by trade. He does some amazing stuff.