Throttle, mixture & prop cables --throw length

This one is expecially for Dan Checkoway, any RV7 builders or otherwise knowledgeable gurus. I bought an RV 7 with a Superior 0360 built by Aerosport. I've now flown it about 150 hours and have always felt something was not quite right about the throttle cable--could not seem to come to slow idle. As I was doing the oil change today, an A&P that has 15 years experience on spam cans was checking my work. He noticed that the throttle was not coming to its stop. After adjusting it a bit, it hit the stop and then would not retract back to the other stop. Same with the prop & mixture. It seems the throws are about 2 1/8". Do I have the wrong cables? Should I order new ones from Van's-- which ones? It seems it needs about a 2 1/2" throw. Thanks for the input.

I had the same issue and drilled a new hole in the throttle arm, and it works fine now.

I run across this problem very often during inspections. You can usually get the proper throw by playing with the cable housing adjustment on the carb bracket to make sure you are taking advantage of the entire cable movement.

Pretty much every bend in a cable will reduce its throw. If the cable is twisting and turning to get where it's going, that's one factor.

The type of cable is another factor. You can purchase custom-made cables from various sources. I haven't gone that route so I don't want to give you bad advice there.

The quadrant or the control is another factor. I started out with a 3-knob quadrant that I bought from Spruce...pretty sure Van's sells it as well. It's the type with round knobs. That quadrant was fairly compact and inexpensive, but it wasn't ideal. The throws weren't long enough...and I had to drill another hole closer in on my throttle & mixture arms.

Then I upgraded to a Dayton Murdock's DJM Mfg quadrant, and that puppy is not only MUUUUCH nicer, but it has larger throws.

That's my brain dump on the topic for now. You ABSOLUTELY gotta have those throttle & mixture controls hitting both stops on the carb or FI servo. Anything else is unacceptable in my book. As tech counselor, when doing FWF inspections that's one of the first things I look for.

throttle cable throw and stiffness at idle

I have a carb with Van's black throttle cable (O320 engine). After pulling idle (at 550 rpm per advise from Mike Seager for 9A) it is hard to push the throttle forward (high resistance for the initial short distance of travel). I read previous postings and am not able to figure out the solution to my problem. Due to the amount of throw I am not able to use the middle hole on the carb throttle arm as shown in the engine installation drawing. I am using the inner hole (shorter arm). The resistance from the accelerator pump and the angle of the throttle arm at the idle position make it hard to move the throttle. Higher idle speed will make the angle the throttle arm a little lower thus better leverage to turn it. However, it also means more floating during landing (this is a long winged 9A). I wonder if anyone has the similar experience and how did you solve your problem. Any advises and suggestions are welcomed. By the way, for the amount of throw I don't see how can one use the middle hole on the throttle arm. Am I missing something?

Aircraft Spruce has cables like the one Van sells but in different lengths and the throw is longer. I'm going to order one since I can't make Van's cable reach and the throw is marginal for my IOF-360 in an RV-7A.
Danny

I ordered a custom cable through Spruce.

DSmith said:

Aircraft Spruce has cables like the one Van sells but in different lengths and the throw is longer. I'm going to order one since I can't make Van's cable reach and the throw is marginal for my IOF-360 in an RV-7A.
Danny

Click to expand...

They had me call the manufacture to give the detail of what I wanted, then they coordinated the purchase. I wasn't able to order direct. I took a long time, so I would keep calling them to make sure they don't loose track of you.

Kent

What's the bottom line on cable throw?

A few years ago, I installed my "second" set of ASC cables for mixture and prop, because the originals were too short for the RV6A with the cables installed horizontal under the main panel.

Mixture would go from stop to stop, and the prop was close to the low rpm stop---- as I remember.

Then last week, I'm told that I should have about a 1/8" gap when the vernier knobs are pushed in all the way. Of course this throws may cables out of wack, no matter what adjusting I do.

Looking up archived responces to this problem, I find that the Van's cable throws of around 2.25 inches is a bit too short. One reponse from someone at Van's a few years back, was to adjust to full idle cutoff, and and let the full rich side, end up where it ends up.

This is fine for me, since I'm at a 4600' airport to start with, and never go full rich except for engine start. By adjusting it that way, I then of course loose that 1/8" gap, because the cable never hits the full rich stop on the carb.

Someone else had told me, that the 1/8" helps prevent the cable from locking, if the vernier knob is twisted while fully pushed in. I haven't experienced this, but it's possible I suppose.

Now for the bottom line. I see posting/replies on this forum from people who do the inspections, and some appear to want full stop to stop, and even an excess percentage of extra cable throw.

My plane is not inspected yet, but will be very soon. Is this just a case of ordering new cables for the 3rd time, to get that 1/8" gap? In all these years, I had never heard of the gap requirement till last week. But who knows, I never knew my gascolator had holes in the four screws for safety wires either...

I'm just wondering what so many others have done, and why Van's didn't supply cables with an extra 1/4".

L.Adamson --- RV6A

Bounce back.

I was taught that when the control is pushed all the way forward that it should bounce back a little. (1/8 inch or so). This is to insure that you are getting full control motion at the carb/TB.

If you need more travel look to see if you can move the cable connection at you carb closer to the center of the attachment. That way the throw that you have will move the control more.

Kent

Throttle cable throw

I have been puzzled by not able to get throttle wide open when I pushed the control forward. After reading threads on cable throw, I kind of settle with the knowledge that I had a bad cable. Not until I read the January 2009 issue of Van's RVator newsletter I found the true reason. In the article Kent Scott mentioned that some builders put F-746 (control bracket) reversed. It is supposed to be one inch behind the instrument panel. Some of us without checking the drawing put it flash with the instrument panel. No wonder my cables were all very tight.

After correcting this problem, my throttle control has plenty of "throw". I can use the center hole on the carburetor arm and still have some extra moment. I was using the inner hole and could not reach from idle to wide open. In case you have the same problem, you might have installed F-746 wrong!

There is alway something to learn: read the drawing!

On my installation (8A, O-360A1A, carb, Van's standard quadrant) I could get full travel on the throttle, but not on the mixture. It was close, but I couldn't get enough adjustment out of the quadrant and cable to get it to move stop to stop. I discussed with Van's and, contrary to what a previous poster was told, they told me that hitting the full rich stop was the important thing and not to worry about the idle cutoff too much. They said if it was close, it would shut down. And so it does.

I'm of the impression that you really do need to hit the stop at full rich to fully activate the "economizer" in the carb that meters extra fuel at full throttle to prevent detonation.

????

I'm making the cables and measuring throws required now. Measuring at the engine first, I need 2 5/8" for the prop, 2 1/2" for the mixture and 1 7/8" for the throttle. I can make these work, but the holes are just barely clearing the top of the throttle quadrant. This one:

https://www.aircraftspruce.com/catalog/appages/RVthrottlequads1.php?clickkey=4196

So, firstly, just wanting to hear from anyone who has had a problem of cables chaffing against the top bolts of this quadrant.

Second issue. The linkage to the rear throttle (RV8) needs to be right on top of the linkage forward to the engine. I plan to overlap two clevis forks there, one going forward and one going aft. Any issues doing that there?