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XT Goes To Full Throttle After Starting Engine

Chortdakooba

Member
Messages
14
I still haven't finished breaking in my engine, and yet another set back with my new XT. This time the throttle servo wants to go to wide open after I start the engine. I tried searching for this problem and can't find any solutions.
Here's what happens. When I just turn on the transmitter and receiver, everything works fine. Throttle works up and down and sets back to neutral. I also just finished putting in an engine kill switch which is working fine. I upgraded to a Futaba 3 channel radio, and at first I thought that was the problem, so I went back to the stock electronics and it did the same thing. Then I thought maybe the kill switch is doing some wonky things, so I disconnected that, but no difference.
I took the throttle arm off the servo and started the engine just so I could see what the servo was doing. It was kind of twitchy, but it didn't seem to move too much to cause a wide open throttle. Soon as I put the arm back on, it seemed to twitch more and back to full throttle.
I just upgraded to a Hitec steering servo. Is this a sign of a bad servo? It was working last weekend. I still have the stock steering servo and going to put that back in to help eliminate the possibilities, but I thought I would put it out there for anyone that as any ideas or maybe experienced the same problem in the past.
Thanks,
 

Chortdakooba

Member
Messages
14
Well it was suggested in another thread that perhaps my clutch spring broke or popped off. I just got to the clutch and it looks fine. Although I don't have the piston stop tool to take it out, the bolts are tight, the spring is not broken or un-attached, and there's plenty of padding left on the shoes. When I insert it back into the housing (bell housing??), the housing still spins freely around the clutch. So that tells me the clutch should be fine.
Anyone with some insight on this? The servo isn't twitching when the power is on only. It only seems to twitch a little bit when the engine is started. That is the throttle servo, the steering servo is working fine.
 

Thwmathue

Well-Known Member
Messages
55
Sounds like Radio interference causing the servos to twitch. Try a different servo also have you set up the fail safe on the radio. Even with a kill switch it's a good idea. Imy not really familiar with the futaba system as I prefer the spectrum dx4c myself. What brand kill switch did you install the dynamite kill switch has some limitations on what Radio receivers you can use with it.I ran into that when I wanted to use spectrum avc with my xb
 

Chortdakooba

Member
Messages
14
Sounds like Radio interference causing the servos to twitch. Try a different servo also have you set up the fail safe on the radio. Even with a kill switch it's a good idea. Imy not really familiar with the futaba system as I prefer the spectrum dx4c myself. What brand kill switch did you install the dynamite kill switch has some limitations on what Radio receivers you can use with it.I ran into that when I wanted to use spectrum avc with my xb

I reverted back to the stock Redcat radio for now, but it was doing the same thing. The kill switch I got was the Redcat one (RRC-05K). The servo doesn't twitch with the power on only. It only seems to twitch after the engine is started. I know the power in the transmitter is good. I did have the fail safe programmed as well, so that it brakes and shuts the engine off when you turn off the transmitter. (did that with both radios). I thought maybe the kill switch was interfering, so I disconnected that but same problem. I still have yet to put the stock servo back in to try it out. I have taken off the drive gear so that at least the tires won't spin out of control if the engine goes full throttle while testing.
Maybe the Hitec servo went bad, but it was working like a champ last weekend. This was before the kill switch was installed.
I also recall when I first got the truck, the steering arm seem to be set a little bit more forward, like 1 position on the post. There was lots of play before it would actually engage the throttle lever on the carb. At least as much as 1/4 or more of depressing the trigger on the trans. When I put the new servo in, I installed the arm perpendicular to the servo so that there was equal travel in both positions for throttle and braking, and the throttle arm would engage more quickly. How is your throttle arm positioned when you turn on the electrics? Is it perpendicular to the servo or a little more forward of that? (ie; more pressure on the brake side)
 

Chortdakooba

Member
Messages
14
Well, it looks as though it was a servo problem after all. I put in the old throttle servo and no problem, no twitching or anything with the engine running. The fail safe and kill switch worked as they should. Just for fun, I even charged up the transmitter just to be sure. However, soon as I connected the Hitec servo, it didn't twitch with the engine off, but twitched like a bugger with the engine running.
For the record, the servo was HS-646WP Hitec servo. It's rated as a high voltage servo, maybe that's the problem?? It's what the local hobby shop had in stock for 1/5 scale applications. It has 6V specs, so I don't know why it wouldn't work.
 

Thwmathue

Well-Known Member
Messages
55
I've never used hitec servos. I prefer savox myself. Sounds like it's a shielding issue with that servo. the coil on the engine can cause EM interference if the electronics aren't shielded
 

Boohunter

Member
Messages
19
I still haven't finished breaking in my engine, and yet another set back with my new XT. This time the throttle servo wants to go to wide open after I start the engine. I tried searching for this problem and can't find any solutions.
Here's what happens. When I just turn on the transmitter and receiver, everything works fine. Throttle works up and down and sets back to neutral. I also just finished putting in an engine kill switch which is working fine. I upgraded to a Futaba 3 channel radio, and at first I thought that was the problem, so I went back to the stock electronics and it did the same thing. Then I thought maybe the kill switch is doing some wonky things, so I disconnected that, but no difference.
I took the throttle arm off the servo and started the engine just so I could see what the servo was doing. It was kind of twitchy, but it didn't seem to move too much to cause a wide open throttle. Soon as I put the arm back on, it seemed to twitch more and back to full throttle.
I just upgraded to a Hitec steering servo. Is this a sign of a bad servo? It was working last weekend. I still have the stock steering servo and going to put that back in to help eliminate the possibilities, but I thought I would put it out there for anyone that as any ideas or maybe experienced the same problem in the past.
Thanks,
Just adjust your brakes thank me later
 

Redredcat0223

Well-Known Member
Messages
149
Location
Glendale,Arizona
It’s def interference with the spark plug believe it or not,I had the same issue and I had read a few other people with similar issues where if it wasn’t a servo acting up it was thier kill switch,there is a plug you should get that’s made for stopping interference but I can’t remember the number off of the top of my head if you google it,it should come right up and I went back to using the Hitec 645mg because I’m only still using my 6v receiver pack but I bought a 6v 5000mah from ddm which works great,the stock pack in my opinion is junk and it’s a 6v 2500mah,hope this helps you out!
 

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