jeff4912

I am nearing the end of my Sig 4 Star 60 build and test fitted the engine and throttle linkage cable from the carb arm on the engine to the servo arm.

The cable is flexible and incased in a plastic sleeve.

The problem is that when I push the throttle up, the flexible cable bows(binds) instead of pushing the cable and opening the throttle. Any ideas to stiffen the cable at the servo end?

The carb barrel on my Evolution 15cc gas engine is also stiff and contributing to the problem. The first 25% of travel to open the barrel is tight and I can't seem to loosen it up enough to stop the flexing (binding) of the throttle cable.

Tried a couple drops of oil and repeatedly working it, but that did not seem to help. Is there a way to get that carb barrel loosened up?

I attached some pics. I would like to make that cable shroud in pic#3 more rigid too because it bends into the bottom of the muffler when the throttle is opened.

av8tor1977

My Feedback: (6)

First off, flexible metal cable like that is not recommended for gas engines due to the possibility of radio interference. Secondly, when you do use those types of cables, the outer sheath needs to be anchored as close to the servo as possible while still allowing enough throw, and at the firewall. Lastly, I have sometimes had to solder a length of solid pushrod to the flexible cable where it goes from the firewall to the carb to help eliminate unwanted flex. You can use a brass sleeve to facilitate soldering the cable to the pushrod. A couple of times I got away with just cleaning the flex cable with flux and wicking solder into that portion in front of the firewall to stiffen it.

You might want to just go to the regular plastic flexible pushrod. It is stiffer than the metal cable.

AV8TOR

All Day Dan

My Feedback: (5)

First of all, if you are detecting a resistance from the carburetor barrel send the engine to where you got it and have them fix the problem. Second, you are not supporting the cable at enough points to avoid flexing. Third, the geometry you are dealing with is working against you especially at the engine. I’ll attach a couple of images of one of my installations to help you out. Dan.

av8tor1977

My Feedback: (6)

Thanks for the pics illustrating what I was saying Dan. Nice setup. And I recommend that plastic pushrod you used over the metal cable, as mentioned before.

His problem with resistance in the throttle setup may be due to sharp bends in the throttle cable in the fuel tank area, as the throttle servo is on the port side of the airplane, and the throttle arm on the carb is on the starboard side. He probably has two sharp 90 degree bends in the cable in the fuel tank area. A better setup would be to have the throttle cable cross over in the receiver area and get to the other side with two gentle 45 degree bends.

AV8TOR

ahicks

My Feedback: (2)

He's likely running into a not so swift carb design. There's a spring that holds the carb barrel against a stop/follower that must be compressed as the carb closes. The groove that stop/follower travels in is not machined real well, making sticky installations pretty easily done (when closing/compressing that spring).

I'd start by changing over to a solid (2-56?) push rod of the type generally shipped with the kits. You might also have a look in the engine owners manual, at the initial carb setup, paying attention to the fact the engine idles with the carb open a little further than most designs. It doesn't need to close completely - not on the idle anyway.

Take your time here. It does need to work reasonably smooth to function well. Keep in mind that when the engine is running, the vibration may work to your benefit with this issue.... -Al

pilotpete2

The Dubro flex cable is an excellent setup, and with 2.4Ghz I see no reason not to use them with a gas engine. In fact my Sig 4 Star 64 and EVO 15cc is set up exactly that way. What I would do is ditch the EZ connector on the throttle end of the cable and solder a 2-56 brass end on the cable and use a nylon clevis to (comes in the Dubro package) connect to the throttle arm. The clevis and threaded adapter will lessen the amount of cable that can flex. Another tip on using those flex cables is to tin the area with solder where you're going to trim it, before you try to cut it. Also tinning with solder can be used to stiffen an unsupported area of those flex cable. Normal electrical solder flows very nicely with that cable.
Pete

rt3232

My Feedback: (6)

Jeff

Something I have done that has worked, for me in a tight install. With the engine removed and the cable free to be pulled out a bit carefully tin the cable back into the area just before the first bend, this will give you a stiff rod effect from your first bend to the carb. also make sure your end point on the servo is correct.

Just a thought

Cheers Bob T
AMA13377

jeff4912

1.Great ideas, thank you.

2. I will tin the cable at the throttle end to stiffen it.

3. Calling Evolution tech support in the morning about the barrel being too tight.

Thanks for the insight into the mechanics of that throttle barrel.

jeff4912

Called Horizon Hobby and they are having me send the engine back for warranty work.

jeff4912

Apparently the throttle barrel was defective, they said they are sending me a NEW ENGINE!

flyinwalenda

My Feedback: (5)

Going forward try and correct the geometry of the pushrod/cable with the throttle arm so it's more at a 90 degree angle.
As already mentioned, support the sheath in more spots and extend it beyond the firewall.
Heat up the last 2" of the cable and flow a bit of solder in to stiffen it up.
Also I would ditch that easy-connect on the throttle arm and replace it with a ball link. Those easy-connects can be/are usually nothing but trouble .

CARS II

My Feedback: (7)

Jeff
soldering the cable is a great idea, I have done that many times, when adding the solder to it make sure you use the paste or liquid to help it solder to the cable good, also when doing it I have a wet rag next to me, as soon as i'm done soldering I run the wire in between the wet rag to cool it and to get all the excess material spread even on the cable and I end up with a clean and a straight.cable.

av8tor1977

My Feedback: (6)

Needless to say, remove cable from the plastic outer sheath before soldering....

AV8TOR

jeff4912

Don't think I can get a 90 degree connection because of the engine mounts.

The 2-56 ball stud thread diameter on the connector from Dubro that I bought are to large to fit into the throttle arm hole on the engine.

Should I just connect with a clevis instead or drill the throttle arm hole larger?

All Day Dan

My Feedback: (5)

Use the 1/16 ball link number 190. Dan.

jeff4912

Thank you Dan!

jeff4912

I followed many of your guys suggestions and soldered a brass connector to the throttle cable (removed the easy connector) and tinned a portion of the cable also.

I then put the ball connector on and the throttle problem now seems to be solved.

I also braced the cable in a couple of places.