mikeburgin
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heres a link to the insite of a carb
The throttle stop screw or idle-speed screw (same thing) determines how far the carb barrel will be able to close when the servo is in the neutral position. Typically you set the servo/throttle linkage so that the carb will go from fully open when the trigger is fully pressed to fully closed when the trigger is in neutral. Then you would adjust the idle-stop/speed screw so that there is a 1-2 mm gap when the servo is in the neutral position. You might need to readjust the spring collars on the throttle linkage to force the throttle arm against the idle speed screw.
Tip#1: If you completely mess up the carb setting and you want to go back to the factory recommended needle setting then you must have the carb fully (Yes I mean fully closed) before you can set the low-speed needle to whatever turns the engine manufacturer suggests. Before you close the carb fully back the low-speed needle a bit to make sure you wont put un-needed stress on the needle seat.
Tip#2: There should be no speed change whatsoever when the car is in idle and when you hit the brakes. If the engine's RPM drop either your linkage isn't set right or the idle-speed screw is set too loose. Tighten clockwise until the carb barrel doesn't move when you go from neutral to full brakes.
Tip#3: Some RTR kits have servo horns that are too small. There is not enough servo throw to open the carb barrel, if you use servo trim to be able to open the carb fully, then when you go to neutral the carb doesn't close enough. To compensate for this the novice engine tuner opens up the low speed needle to drop the engine RPM so the car will stay still when at idle... The drawbacks of correcting the linkage problem with the mixture control is that now the low-speed is too rich and the car won't idle for more than a couple of seconds before the engine sputters and dies.
To fix this problem you need to get an after market servo horn that is larger yet still fits your particular servo brand. Now you can go from fully open to fully closed, without using trim. Now you wont have to compromise the carb settings because of lack of servo throw.
Low-Speed Needle:
Thanks to http://www.nitrorc.com/ for saving me some typing
The throttle stop screw or idle-speed screw (same thing) determines how far the carb barrel will be able to close when the servo is in the neutral position. Typically you set the servo/throttle linkage so that the carb will go from fully open when the trigger is fully pressed to fully closed when the trigger is in neutral. Then you would adjust the idle-stop/speed screw so that there is a 1-2 mm gap when the servo is in the neutral position. You might need to readjust the spring collars on the throttle linkage to force the throttle arm against the idle speed screw.
Tip#1: If you completely mess up the carb setting and you want to go back to the factory recommended needle setting then you must have the carb fully (Yes I mean fully closed) before you can set the low-speed needle to whatever turns the engine manufacturer suggests. Before you close the carb fully back the low-speed needle a bit to make sure you wont put un-needed stress on the needle seat.
Tip#2: There should be no speed change whatsoever when the car is in idle and when you hit the brakes. If the engine's RPM drop either your linkage isn't set right or the idle-speed screw is set too loose. Tighten clockwise until the carb barrel doesn't move when you go from neutral to full brakes.
Tip#3: Some RTR kits have servo horns that are too small. There is not enough servo throw to open the carb barrel, if you use servo trim to be able to open the carb fully, then when you go to neutral the carb doesn't close enough. To compensate for this the novice engine tuner opens up the low speed needle to drop the engine RPM so the car will stay still when at idle... The drawbacks of correcting the linkage problem with the mixture control is that now the low-speed is too rich and the car won't idle for more than a couple of seconds before the engine sputters and dies.
To fix this problem you need to get an after market servo horn that is larger yet still fits your particular servo brand. Now you can go from fully open to fully closed, without using trim. Now you wont have to compromise the carb settings because of lack of servo throw.
Low-Speed Needle:
Thanks to http://www.nitrorc.com/ for saving me some typing
