Some expert help requested

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johnnycosmos

RC Newbie
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Hi,

I have a little nitro RC and it starts great. But it immediately goes into full full throttle and screams.
The throttle goes straight to fully open and I can't control it.
The servo seems to not be attached to the throttle in the usual way. Picture attached.
Any thoughts? has this been rigged like this on purpose?

Many thanks

John
120471
 
Hi John,
Can you take some pictures of the throttle linkage attached to the carb? It might give a better picture.
I had the same problem recently and needed to adjust some spring tension.
 
Check an see if the throttle trim on the transmitter has been turned all the way up ,also ,you can reset the throttle
linkage horn by removing it from the spline an turn it back some!

That also don't look right ,there should be two linkages ,one that goes to the brake ,an one that goes to the
throttle ,the also should have some tiny springs tension springs on the linkage rod with rod collars!
 
Hi,

many thanks for responses. I attach a couple more pictures.
The throttle servo does work and it moves the brake linkage back and forth. However the throttle linkage doesn't move. It looks to me that the throttle linkage isn't connected to the servo in the same way as the brake linkage. The resting position is the throttle open about 1.5mm. But when I fire it up it goes to full throttle and screams the servo has no effect.

Many thanks

John
 

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Since the idle speed screw seems to be set correct, close the high speed needle all the way (count the turns), and back it out 3 1/2 turns. Turn the low speed all the way in (count the turns), back it out about 1 1/2 to 2 turns from closed. Start the engine, if it still goes wide open throttle, then you may have a broken needle. Also, you could have a bad air leak causing the engine to run lean.

One step at a time.

Hope this helps.
 
Hi,

So I've investigated further. If I disconnect the throttle linkage from the servo the servo does move as I'd expect. The problem is that if you open the throttle with the remote it doesn't spring back when you release the remote. Where does the energy come from to close the throttle. Does the carburettor have a return spring or is the servo suppose to 'pull' it closed? Am I making sense? Do the servos need lubricating?



John
 
I think that the little arms on those old style carbs maybe adjustable ,I can't remember .I would have to check mine!
But if so ,then you may can loosen that tiny nut ,an adjust the arm in its proper place ,also ,the arm may have slipped.

Also ,the engine looks gunky ,make sure that the carb barrel is not sticking!
 
i can honestly say that throttle servo linkage is the first like that i have seen, what vehicle is this?
 
i can honestly say that throttle servo linkage is the first like that i have seen, what vehicle is this?

LOL....it is funky lookin ,as I noticed it too ,it almost looks like a steering servo saver in which ,that maybe his
problem!
If the saver itself isnt properly put together ,or even if someone else had forced a larger screw into the horn ,
it could cause jamming ,lol.....I had done that before ,so I would know!
 
Hi,

So I've investigated further. If I disconnect the throttle linkage from the servo the servo does move as I'd expect. The problem is that if you open the throttle with the remote it doesn't spring back when you release the remote. Where does the energy come from to close the throttle. Does the carburettor have a return spring or is the servo suppose to 'pull' it closed? Am I making sense? Do the servos need lubricating?



John

All servo's should return back to its neutral center place when the trigger device is released ,the servo is being jammed
by something causing it to labor!
 
Hi,
Had a bit of time so have got back to my misbehaving Tiger.
The servo seems to work ok and the brake linkage moves back and forth fine. The throttle linkage though doesn't move the carburettor. The throttle linkage attaches to a horn on a collar on the server. The collar has a metal band which bulges when the server rotates but doesn't move the horn and hence the carburettor arm doesn't close or open. The carburettor moves freely on its own. Seems to me that the metal collar should be the spring but isn't effective.
This is the set up on the servo

https://www.ebay.co.uk/itm/PD9108-T...a=0&pg=2047675&_trksid=p2047675.c100012.m1985

Should the metal band bulge? is it supposed to be spring?

If anyone understands my explanation then you're a genius. Any advice gratefully accepted.

Kindest

John
 
Disconnect the servo arm from the throttle and see if the linkage will open and close the carb effortlessly. If not, that's your problem. It's sticking. Keep us posted.
 
Have you tried taking the servo horn apart and look for broken parts? if nothing else you can clean it and make sure it is working
 
Good Morning,

Thank you.
When disconnected from the servo the carb opens and closes freely.
It's not immediately obvious to me that any parts are broken apart from the fact that the 'collar' rig (link from earlier) doesn't appear to be doing its job.
I thought I might just get a new linkage and do a more simple trad rig with throttle and brake both linked to same 'butterfly' on servo.
Most grateful for your insights.

Kindest

John
 
BTW Would anyone know what model it is?
The engine is a Thunder Tiger Pro and I think the car is a Tomahawk but can’t find a model number. Servos are ACE S1903.
As ever thank you.
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That car looks too clean ,an appears that someone never got it going an gave up on it!
The tires looked like that they was not glued!....?
 

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