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Old 12-14-2009, 02:14 PM   #1
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Default Planning on replacing throttle servo. Help?

Hi. I have the Losi LST1 truck which has the JR Z270 throttle servo. I thought that the included throttle return spring that came with the truck wasn't strong enough (it couldn't close the carb) so I replaced it with 2x Goody Ouchless rubber bands. They were a lot stronger than the spring, and managed to close the carb unlike the spring (but of course when I say "closed" there was still a 2mm gap for the engine to breath).

However, with the new rubber bands, the throttle servo didn't even manage to open the carb 50% when I applied full throttle, it wasn't strong enough. I've heard about you guys using 2x Goody Ouchless's + having a servo that "can lift a house". So I'm wondering, can you recommend me any throttle servo I could replace with? I was thinking about one from JR since my radio is the JR XS3, and the other servos on the truck ar from JR aswell.

Take a look at this page, how do I know if my servo is sub-micro, micro, mini, mid, standard or High voltage?: http://www.jrradios.com/Products/Servos-Air.aspx

P.s. I have a digital servo system + radio!
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Old 12-14-2009, 02:20 PM   #2
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get a HiTec 7955tg its plenty strong and reliable!

I run 7950 for str and 7955 on throttle with a lipo rx pack.
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Old 12-14-2009, 02:30 PM   #3
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Originally Posted by xjqkz View Post
get a HiTec 7955tg its plenty strong and reliable!

I run 7950 for str and 7955 on throttle with a lipo rx pack.
Thanks for the quick reply! My current throttle servo has 45 oz/in torque but HiTec 7955tg has 333 oz/in xD Cool!

But one question man, my current throttle servo is 0.73" x 1.55" x 1.46"
and the HiTec one is 0.78" x 1.57" x 1.45". So, it will be no problem installing it? And also, will this one work with my JR XS3 radio? Thanks buddy!
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Old 12-14-2009, 02:35 PM   #4
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7955 is the way to go, yes it will work in your truck and with your radio

Also make sure that your slide isn't binding. If the throttle return spring wasn't fully closing it, that makes me thing something is binding
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Old 12-14-2009, 02:40 PM   #5
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Originally Posted by pickle311 View Post
7955 is the way to go, yes it will work in your truck and with your radio

Also make sure that your slide isn't binding. If the throttle return spring wasn't fully closing it, that makes me thing something is binding
Sorry, what is binding exactly?
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Old 12-14-2009, 04:42 PM   #6
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Originally Posted by helgso View Post
Sorry, what is binding exactly?
It could be that your linkage is at an angle enough to pull the slide a little crooked. (They tolerate some angle of course...) Also... If the carb is the same as in the Sportwerks .26 V2 (same engine as the Losi Mach 427) you might think about taking the slide out (just remove the idle screw) and deburr the edges of the slot that the idle screw sits in. You can use sandpaper, a file, or even a few good scrapes with a hobby knife to just VERY SLIGHTLY chamfer the edges. Be sure to clean it VERY well after- you don't want metal shavings in your engine!
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Old 12-14-2009, 04:46 PM   #7
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p.s. I agree on the 7955. That servo rocks. I use it on steering, and use the older version (5955) on throttle.

They're strong enough to bend or break aluminum servo horns, so 2 tips: Make sure your endpoints are set right... and when you are messing with them, DO NOT get your fingers between the servo arm and anything else.
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Old 12-15-2009, 04:27 AM   #8
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It could be that your linkage is at an angle enough to pull the slide a little crooked.
Let me try to explain. When LST is stock-built, the low speed needle is behind a knob that is used to change between HI and LO gearbox settings. When I sealed the engine, I decided to rotate the carb a bit, so the LSN would not face the knob, and because of this, the throttle servo's pull is not as straight as I would like it to be, that's why the throttle return spring couldn't close the carb, and that's why my current throttle servo isn't powerful enough anymore :P

I did not rotate the carb much, just very little, and the pull is not sideways or anything, just not exactly straight, but yet straight. So yea, I guess I have a binding.

But I don't understand what you mean by "deburring" it. You want me to remove the idle screw, take something rough and rub down or polish the part of the carb that loosens when the idle screw is out? And what, will that make the slide easier to move inside the carb resulting in a less-resistance pull?
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Old 12-15-2009, 04:56 AM   #9
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Originally Posted by helgso View Post
Let me try to explain. When LST is stock-built, the low speed needle is behind a knob that is used to change between HI and LO gearbox settings. When I sealed the engine, I decided to rotate the carb a bit, so the LSN would not face the knob, and because of this, the throttle servo's pull is not as straight as I would like it to be, that's why the throttle return spring couldn't close the carb, and that's why my current throttle servo isn't powerful enough anymore :P

I did not rotate the carb much, just very little, and the pull is not sideways or anything, just not exactly straight, but yet straight. So yea, I guess I have a binding.

But I don't understand what you mean by "deburring" it. You want me to remove the idle screw, take something rough and rub down or polish the part of the carb that loosens when the idle screw is out? And what, will that make the slide easier to move inside the carb resulting in a less-resistance pull?
Yes. The part that is pulled by the throttle linkage. You have to pop the rubber boot loose too of course... that will slide all the way out when the idle screw is removed.

It has a slot cut in it that the idle screw sits it. The edges of the slot can be a little rough and cause it to catch. Just smooth those sharp edges up just a hair.

Treat it very gently! You don't want to bend the brass needle that controls the fuel flow!

And try to get the pull on the carb linkage as straight as you can too. It may involve taking the linkage loose from the servo horn and moving it... then resetting endpoints of course. Note that the pull is NOT a straight line in line with the rod... it is a straight line from the end of the ball link to the center of the bolt that attaches it to the servo horn. You can also rotate the fitting that the ball link connects to on the carb slide by loosening the tiny set screw opposite the ball.

Hope that helps.
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Old 12-15-2009, 07:04 AM   #10
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Mission accomplished. Loosened the idle screw and got that slide out. I took a look at the edges, but they were quite smooth already, I barely didn't do anything to the slide but clean it. When installing it back on the carburator, should I oil the slide with WD-40? But of course not too much of it :P
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Old 12-15-2009, 07:30 AM   #11
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Mission accomplished. Loosened the idle screw and got that slide out. I took a look at the edges, but they were quite smooth already, I barely didn't do anything to the slide but clean it. When installing it back on the carburator, should I oil the slide with WD-40? But of course not too much of it :P
I don't like WD-40 on nitro engines. A little after-run oil or even just a splash of nitro fuel maybe.
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Old 12-15-2009, 07:32 AM   #12
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Basically you want to take the sharp edges off the slot... that's the point. They may feel smooth, but just a tiny, miniscule rounding of that sharp corner will help. Almost so small you can't see it.
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Old 12-15-2009, 08:01 AM   #13
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Quote:
Originally Posted by DOMIT View Post
Basically you want to take the sharp edges off the slot... that's the point. They may feel smooth, but just a tiny, miniscule rounding of that sharp corner will help. Almost so small you can't see it.
I only have a very rough piece of sandpaper, I tried using it a bit but I could see I was scratching the slide where I was trying to evening out the edges. is that allright? :P

EDIT: nevermind, got the job done with a knife :P

Last edited by helgso; 12-15-2009 at 09:34 AM.
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Old 12-15-2009, 02:56 PM   #14
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Hey Domit are there any indoor tracks in the dallas/fw area? I'll be visiting family over the holidays, it would be cool to burn some nitro with my cousins. One of them just got into the hobby after he saw my buggy.
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Old 12-15-2009, 03:47 PM   #15
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Hey Domit are there any indoor tracks in the dallas/fw area? I'll be visiting family over the holidays, it would be cool to burn some nitro with my cousins. One of them just got into the hobby after he saw my buggy.

I believe Mikes is indoor
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