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Throttle binding

WingnutWick

Well Known Member
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.


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.
 
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.
 
Also I read somewhere about that if the accelerator pump goes bad it makes the throttle tighter.

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

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.

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

msobx2.jpg

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

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.
 
Yep, it does....here’s a photo.

I think you might have mis-understood the point. The cable connection to the throttle lever on the quadrant must be below the pivot so that when you advance the throttle lever, it pulls the cable.

If you attach the throttle cable to the lever above the pivot of the quadrant, then when you advance the throttle lever, it will push on the cable.

Oh, and as RocketBob said, the cable attachment to the throttle arm on the carburetor is usually with the cable end threaded and a clevis fitted to the end of it. The clevis pin goes through the throttle arm on the carburetor with a cotter pin.
McFarlane makes really good throttle cables. When I need to replace my green Vans-supplied cable next time, I will get one from McFarlane.
 
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It may be just me but that throttle cable setup is giving me the shivers just looking at it :eek:
I would not use that type of cable on the throttle. I have seen that type bowden choke cable style break. Why not stop, take a step back and make some safety improvements while you have the cowls off.
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

As the others have said why not change the cable out to the correct length push pull throttle cable from Spruce or Mcfarlane with threaded ends on both ends to mount clevis or rod end fittings. You will find it will work much smoother than the choke cable style and especially if you drill the quadrant lever ABOVE the pivot and re route the cable to push rather than pull to advance the throttle. You will have to fashion a cable support bracket to hold the cable end near the REAR of the carb but that is not too difficult(add the mixture cable to it as well while you're at it). Vans may even sell one you can modify to fit this engine ( everything has to be modified to fit this engine!)

The mixture cable attachment is hard to see in the photo but looks to be a bugnut arrangement with a nyloc nut securing it to the bottom of the arm? This is a big no no in the Heat/Oil/Fuel environment under the cowling.The bolt is also too short with the nut at the end of the thread. Use a metal lock or better still castellated nut with cotter key.
I do use this type of cable and the bugnut arrangement you show on your throttle cable on my own mixture cable but mitigate the risk of cable breakage by using a mixture return spring from a Robinson R22 Helicopter. If the cable breaks or comes loose the spring pushes the mixture arm to full rich. Search for "Mixture Control Safety Spring" Part # A071-2 = Spring and associated hardware. It was a Service Bulletin for Robinson in 1984. https://robinsonheli.com/wp-content/uploads/2015/12/r22_sb41.pdf

Good Luck

Flying a H2AD in an RV6 for 14 years and luvn it.:D
 
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It may be just me but that throttle cable setup is giving me the shivers just looking at it :eek:
I would not use that type of cable on the throttle. I have seen that type bowden choke cable style break. Why not stop, take a step back and make some safety improvements while you have the cowls off.

Ditto that :eek:
 
Great!!

Hey guys - all great info and suggestions! It also confirmed what I was thinking about it to begin with. Again, we just got this plane and these cables were re-done right before hand due to binding and nothing mentioned in the pre-buy about the fact that they are basically the same connectors I used to use in model RC airplanes.

I am in the process of getting everything dialed in on this new plane and done correctly and this is one of them. I will be converting the connection to above the pivot (hopefully there is enough space - otherwise I'll change the quadrant), and use all appropriate cables and hardware as per your suggestions.

Thank you all for the input!

Much appreciated!

-Charles
 
Tracking

Yes - I'm tracking that. Drill a hole above (if there is enough room) the pivot on the quadrant side inside the cockpit above the pivot to make it a direct push pull and replace the cables with legitimate cables and connections.

I think the pivot is right there at the top of the cover so I may have to modify it all and move the actual pivot lower if that's a possibility. Otherwise some sort of bell crank or throttle armature to reverse the throw inside the engine bay.

Thanks all!
 
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