Throttle binding
 

Hello,

Troubleshooting a few gripes on the lady?s new RV-6A with an O-320 H2AD and one of them is that the throttle cable seems to be binding a bit. This issue occurred before we purchased the plane and was fixed with new cables for mixture and throttle. Throttle was smooth. I had the cowling off putting in new plugs and when I put it all back together the throttle seems to have gotten a little stiff again with a ?gritty? ?grinding? feeling and more force than normal needed to move the throttle. A couple times the cable bent just in front of the throttle handle a couple times. Thankfully it wasn?t crimped when that happened.

I pulled the cowling back off and that helps make it a little more smooth but still a little tighter than normal, albeit no gritty feeling. Of note, her quadrant is the lever type not the push pull which requires the throttle and mixture to be routed around the left side of the carb and bend around the front of the carb and backwards connecting on the right side of the carb. I?m sure I would have no issues with a push pull setup as that would be a direct straight connection.

When I put on the cowling they do get pushed up a bit. I?m assuming this is causing the extra friction to make the gritty feel.

My questions are:
1. Looking for general insight from anyone with this setup where you have to route around the front to make throws in the correct direction.
2. I was thinking of shortening the throttle and mixture cables to hopefully bring it closer to the engine and away from the cowling but I am not sure how much bend I can induce? Thoughts?
3. Anyone know of any smart ways to get around routing around the front of the carb?

Any other insight is warmly welcome!

Thank you!

Charles

I would consider installing a belcrank either under the cowling or under the instrument panel to reverse direction of the cable operation.

I wouldn't be comfortable with such a long cable dong a 180 under the cowling.

Belcrank
 

Yep, I don?t like it either. Has anyone done this before? Do they make these specifically for this application?

Also I read somewhere about that if the accelerator pump goes bad it makes the throttle tighter. The mixture control which runs essentially parallel with the throttle is fine.

Vans does make a small bell crank that might help. It is intended for the mixture control on the Bendix FI (RSA-5) installations, and it reverses the sense of the mixture control. It has a bracket that mounts to some points on the engine case and cylinder.

Not sure it will help you directly or need some modification, or just be a starting point idea for making your own that is specific to the application.

There was a recent discussion here about that and I?ve experienced it with my 6. Resistance that felt like it was in the throttle cable was found to be caused by dryness around the accelerator pump shaft. A shot of lube on the pump shaft and it?s resolved. Disconnecting the throttle cable at the carby is a simple way to check if this is the cause of your friction.

You could remake the throttle quadrant lever so it extends below the pivot and attach the clevis below so it reverses.

Look into installing the proper quadrant that would push the cable instead of pulling it, and using short direct cables that connect to the carb from the back side.
https://www.vansaircraft.com/cgi-bin...oduct=quadrant and... https://www.vansaircraft.com/cgi-bin...uct=ctq-cables

I think that is his current problem, the cable connects at the bottom, under the pivot point.

Photo
 

Yep, it does....here?s a photo.

Then it can be reversed by drilling a hole in the proper position above the pivot. I've made throttle quadrants from scratch and have a solidworks drawing to determine the hole position.

Cable setup looks sketchy. I would get the correct push/pull cable from Spruce along with a clevis. They use teflon-lined bowden cables for those, which is available via special order if one just wants the raw cable.