Starting idle opening on a 257 carb?

[Mike Cathey]

I'm setting up the throttle linkage on a Gizmo 30.5 with a 257 carb in a gas scale. What's the starting point idle butterfly opening?

 

[Rich Jones]

I like to use the outside (high) needle as a guide. I set the tip of the carb arm a little bit to the left of that needle. It is kind of trial and error but that is a good starting point for me.

 

[Dave Gilles]

1/4"

 

[Mike Cathey]

Between the butterfly and the barrel correct?

 

[Mike Cathey]

Also, I have also been told that you don't want to get off the throttle too quickly at lower speeds because the gas motors are prone to dying. So, is it wise to slow down the servo speed in that direction as a preventative measure?

 

[Daniel's Racing]

Also, I have also been told that you don't want to get off the throttle too quickly at lower speeds because the gas motors are prone to dying. So, is it wise to slow down the servo speed in that direction as a preventative measure?

Not true at all. On and off throttle as fast as you can should never cause the properly tuned gas engine to die. Zero truth to that.

A very small crack is all it takes to idle. Close it tight and just a couple clicks of trim from there.
Not sure what Dave meant by the 1/4" but it takes nothing like a 1/4" of anything from closed to idle opening. Guessing he meant end of carb arm, pushrod or something but it is a bit less than that for sure. Closed and then barely cracked is where it will idle at. Screw idle screw back in it. Like 1/2 turn max after contact would be a good start to judge a idle spot with butterfly. Maybe he meant a quarter turn of a idle screw. ???

 

[Dave Gilles]

1/4" on your carb arm thing. This isnt rocket science it doesnt even need discussed after the first time you fire the engine up.