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Carb Parts 
Book  SP & DP

Carb Body Late

Tinning Solex carbs

Solex jets

Solex Carbs

Rebuild Kits

    11/14/08*

Answer---> The idle jet is properly referred to as Bypass Air Cut-Off Valve and the small pointed one was used in the single port Solex carbs and the dual port carbs had an aluminum mushroom end with no jet on the end. (It just closed off the idle passage)  The earlier single port Solex carburetors had just a small idle jet or "Pilot Jet" with no cut off. This is the one we recommend using on the single port Solex carbs because it's simple, cheap and works. Now even the new Brazilian Bocar single port carbs  use the late model electrical cut off valve, so be sure you know which carb you have before ordering parts. The reason this electric cut off was used in the first place was to help stop pollution. In other words if your motor is in bad need of a tune up  or an overhaul, this little valve will keep it from running on after the key is shut off. Several things that cause this "run on" are excessive carbon in the combustion chamber or something sharp that acts like a glow plug. (end of a Helicoil spark plug insert) So if you keep the motor in tune and descent shape this device is not needed.
  If the electrical cut off valve gets a little loose or goes bad then the motor won't  idle and will keep dying at low speeds. (remember it must be grounded through the threads to the carb body so don't use any Teflon tape on these threads) 
 On some of the early type electrical cut off valves ( that had a small pointed brass rod coming out the end) you could just cut tip off and keep using the jet, but with the later type valve with the aluminum end, it must be in the system and pulled back by the solenoid. (it can be modified to always be in the out position but requires  more work to modify it then it's worth)    See carb parts page -> # 57, # 58 & # 40
If the motor will not idle it might also be wise to check for a plugged jet even if the solenoid is working.
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