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Benchtop Basics 101>Episode 5>

Benchtop Basics No. 5

17.5 mm Carburetor setup tips


Initial settings for the 17.5 mm carb (left side of carb):

  • Center screw (idle position screw): 4 full turns from fully closed.
  • Right screw (air mixture bleed screw): 3 and 5/8 turns from fully closed.
  • Use the tapered needle (A 8), installed with the clip in the center notch position.

Use the #90 or #92 main jet, depending on your bike's level of modification.  You may need to change this jet further, if you are unable to obtain satisfactory tuning results.  Consider acquiring even number jets to 100 for general tuning purposes.
Note: These are rough initial settings ONLY.  You MUST properly tune the carb to YOUR bike by testing and riding the bike, to properly determine correct jetting and needle placement.  Jetting should be verified by "e;reading"e; the spark plug (see the TechFAQ -
Mid-South MiniMoto Tech FAQ for more info on reading your plug).
Failure to verify mixture settings may result in a lean condition, and cause engine failure.
To lean the mixture at lower RPMs, lower the needle further into the jet, by raising the clip's position on the needle.  To richen the "e;bottom end"e;, raise the needle further out of the jet, by lowering the clip.


Setup and operation notes:

The black knob is the choke, you must pull up and turn the knob ΒΌ turn to set the choke.  Release is NOT automatic, you must release the choke manually. In later model packaging for this carburetor, the choke mechanism must be user-installed (it comes in a small parts bag).
The fuel inlet line fitting is located next to the choke knob.  The small hose dangling from the carb is a vent hose.  You may route this hose to a vent canister if desired, or required for racing. The fitting adjacent to the vent hose should be capped.  Do not uncap any vacuum fittings that come capped.
It is not necessary to cap the two left-most fittings across from the vent hose (these exposed vacuum fittings are unused in this application, and do not open to the inside of the carb).  The brass fitting located at 12 O'clock on the manifold side of the carb should be capped.  Later model packaging includes the cap for this fitting in the small parts bag.  Be sure to install the cap, if it is not already fitted.
The stock 14mm throttle cable WILL NOT WORK with the 17.5 mm carb.  If your kit does not include a 17.5 mm cable, purchase the proper 17.5 mm throttle cable (see our online catalog underPocketbikes & Parts
Use the appropriate chrome cable guide elbow for your application (you will likely need to install the shorter one).  Be careful when installing or removing them not to put any side-loads on the tubes - they are made of BRASS, and can bend or break if mishandled.
Mid-South Minimoto stocks a full range of jets to fit the 17.5 mm carb should you require something beyond the scope of the jets enclosed with the kit.

This information is the intellectual property of Mid-South Minimoto and may not be reproduced, in whole or in part, unless authorized with the express written permission of Mid-South Minimoto.
Copyright 2000-2004 - all rights reserved.

This information is provided in good faith as a guide. We are not responsible for any typographical or informational errors or omissions.  Due to the many mechanical and technical variables, this information is to be used only as a guide, and is in no way guaranteed to be accurate or applicable to your engine, your bike, or your world in any way.

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