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Old 09-07-2007, 05:12 PM   #1
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Default Throttle Servo ?

I have a couple of questions that I was looking for help with.
I was breaking in my new O.S. .28 truggy motor yesterday and my throttle servo went out. It was an Airtronics 94358 high torque (however, it was about 3 years old and had been used alot). When I got the motor the the carb was sticky so I dropped some afterrun oil down it and it seemed to loosen up. However, the carb sits at a weird angle to get it to fit in the truggy without hitting the center diff set up. The servo seemed to pull the carb smoothly after some tinkering with the linkage. Well I had to buy another servo, but before I put it in I had a few questions.
1) Should the throttle servo have lasted longer, or is this the average life? (Yes I did have the EPA set correctely)
2) Is there anything I can do to make the slide carb move more freely?
3) Is there a way to rotate the small ball that the servo hooks up to on the carb?
4) Would there have been enough binding in the way I had the throttle linkage set up to cause the servo to fail even though it felt preety smooth?
Thanks for taking the time to read this any info would be appreciated.
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Old 09-08-2007, 01:36 AM   #2
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the small ball has a set screw on the opposite side loosent hat and you can move the ball to a better position
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Old 09-08-2007, 03:52 AM   #3
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When viewed from the front, your linkage arm should be parallel to the chassis. Adjust the ball on the slide to get this.

When viewed from the top the linkage arm should be in line with the centerline of the slide. Get this by rotating the carb until the rod lines up with the slide. You may need to readjust your ball on the slide to get it lined up both ways. What you are after is getting a full pull on the slide without bending an imanginary line between the link rod and slide centerline in both the horizontal and vertical plane. Set your EPA real low, pull full throttle and start running the EPA out til you get a full pull and the servo starts to buzz, then walk it in a point at a time until the buzzing stops.

You mentioned having to turn the carb at a weird angle to clear the center diff. You may be able to move the linkage to the opposide side of the servo horn to correct this. Under if it's on top, or on top if it's currently mounted under the horn. You will need to redo all the above if you flip the linkage on the horn.

Sorry if this sounds confusing, it's simple to show someone, but not so easy to describe.

Here's a pic that might help make some sense of the description.
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Throttle Servo ?-linkage1.jpg  
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Old 09-08-2007, 07:33 AM   #4
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fhm555, I don't see any throttle return springs on your car.
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Old 09-08-2007, 05:22 PM   #5
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Thanks for the help. I thought that the throttle linkage should be perpendicular to the chassis, now that I know how to move the carb linkage ball I should be able to set it up right.
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Old 09-09-2007, 04:10 PM   #6
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Quote:
Originally Posted by satoch View Post
fhm555, I don't see any throttle return springs on your car.
First, it's not my car, and you also don't see an air filter because the car was not done when I took the pic. It's one I built for a guy several years ago and the pic was originally taken to show someone how to set up the brake linkage on an MP 7.5 K car.

As far as that goes, you won't find any return springs on any of my cars since I started using GMK Carb-o's. They work just as well as a spring and are much simpler and easier to install. No need to hunt or rig a spring anchor point or find a spring that's not too whimpy to close the throttle, and not to stout to ruin the throttle servo. The GMK units make runaway prevention a no brainer, just slap on a carb-o or two and your done.
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