Audioguy

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Finally got the low speed carb adjustment to work on my 8N. Removed the idle jet completely and still had to adjust the idle screw all the way in for best idle. Turns out the circuit in the carburetor body base was about .020 which was much smaller than the .035 idle jet. So I got out the pin vice and drilled out the port, one number drill at a time, until I got to .040. The idle mixture and the main needle are both now set at about 1-1/2 turns out and it idles down to 400 RPM with no problem. Thanks to all you carbologists on this site...could not have done it without you.
a156404.jpg
 
(quoted from post at 21:35:43 04/03/17) Finally got the low speed carb adjustment to work on my 8N. Removed the idle jet completely and still had to adjust the idle screw all the way in for best idle. Turns out the circuit in the carburetor body base was about .020 which was much smaller than the .035 idle jet. So I got out the pin vice and drilled out the port, one number drill at a time, until I got to .040. The idle mixture and the main needle are both now set at about 1-1/2 turns out and it idles down to 400 RPM with no problem. Thanks to all you carbologists on this site...could not have done it without you.
a156404.jpg
here are two of those idle ports, both fed from the idle jet, one above the throttle plate and one below it. They are smaller than 0.040 in all M/S carbs. I guess if it works for you..........
 
Ineffectiveness of the low speed idle screw is almost invariably caused by air leaking past the throttle shaft due to wear in the air horn bore.

What you have done is increase the amount of idle air allowed by the idle screw to compensate for such wear.

Dean
 
Thanks for all the input. Actually this carb has a new throttle shaft and seal, the seal flange is facing the outside, hopefully the vacuum in the throat will help the seal to work.
 
It will help temporarily but will not solve the problem. The wear is in the air horn bore rather than the throttle shaft.

Will the engine idle at 400 RPM?

Dean
 

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