Author Topic: AMAC carb idle speed  (Read 2519 times)

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Offline steveale

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AMAC carb idle speed
« on: 21 Mar 2016 at 14:18 »
I have the exact carb in the attached picture.  The throttle and air slides work within full range.  When I am sitting in neutral with open air and throttle closed the motor still runs at relatively high speed.  I can close off some air and the motor will idle down but doesn't run as well.  I am running at full advance on the mag and have not tried to retard the spark because my cable needs attention to function properly.

Is there any other know way to control idle speed on the 2 3/4 machines with this specific carbie?   It is a 1913 douglas btw...

Offline eddie

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Re: AMAC carb idle speed
« Reply #1 on: 21 Mar 2016 at 15:36 »
Steve,
          Look carefully at the bore for the slide - if it is worn, it will probably have a step at the back, just above the bottom of the inlet tract. When this occurs, the slide will operate correctly with the engine stationary - with the engine running, the suction pulls the slide against the back of the carb and prevents it from dropping over the step - resulting in a fast tickover. You may be able to ease the step with a small scraper, but a better solution is to have the carb body bored and fitted with an oversize slide. I ran my 2 with a worn carb for several years, but ended up having to 'play tunes' on the valve lifter to control the revs!! A cheapskate way of making an oversize slide is to turn down the original and then soft solder a sleeve onto it - then cut out the guide slot.
  Regards,
               Eddie.

Offline steveale

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Re: AMAC carb idle speed
« Reply #2 on: 21 Mar 2016 at 15:47 »
Thanks Eddie, I'll check out the bore tonight.  I don't recall seeing a step but I wasn't looking specifically for it either.  The throttle body is a bit weird with the angle taper at the bottom which allows the air passage at closure.  I guess it's akin to the round tapers you see in the more modern slides.

Offline cardan

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Re: AMAC carb idle speed
« Reply #3 on: 21 Mar 2016 at 22:30 »

On early bikes it's common to retard the ignition to slow the idle speed, not to mention improve slow running and hill climbing, so it's certainly a good idea to get the magneto control working properly. However if the throttle lever is closed completely the motor should stop. If not, your throttle cable is too short, or the slide is a poor fit in the body of the carby.

Leon

 

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