Model Engine Company of America
How to Adjust the Square K&B Carburetor

The style carburetor on left was used on the K&B 40, K&B 61 and K&B 7.5 outboard engine.

The style carburetor on right was used on the K&B .67, .82, 1.00 inboard, outboards and ducted fans.

First of all how many turns out an needle valve should be is an arbitrary starting point and  should not be considered a correct setting. If we knew exactly how many turns out a needle should be set you wouldn't need a needle to adjust. You have learn the sounds an engine makes tune your engine properly.
A good starting point for the main needle is about 4 to 5 turns out. To adjust the main needle loosen the lock nut slightly and turn the main needle in. clockwise, until it stops. DO NOT FORCE IT. You could place a piece of fuel tubing on the fuel inlet nipple and blow through it and screw it in until the flow stops, be sure the throttle barrel is in the full open position. Now unscrew the main needle 4 to 5 turns.

Next set the idle needle with the head about flush or slightly protruding from the brass receptacle it screws into. DO NOT TRY TO SCREW THE IDLE NEEDLE IN UNTIL IT STOPS. Doing so can ruin the spray bar end and make it impossible to obtain a correct setting.

The barrel stop screw does just that. It stops the barrel from closing completely and it also is a cam screw as it rides in an angled groove which allows the barrel to move in and out as it's opened and closed. See Carb Designs


Typically you will see a gap between the end of the idle needle and the end of the spray bar with the throttle in the full open position. This gap is usually 1/16" or slightly more.


Now proceed to:
"How to adjust an aero engine carburetor" or "How to adjust a marine engine carburetor"


The above information is provided as a guide. Since MECOA/K&B has no way of determining the ability of the individual using and understanding this information, we assume absolutely NO RESPONSIBILITY for any damage to person or property from the use of this information.
 

©2004-2008 Model Engine Corporation of America, All rights reserved.
MECOA and K&B are Registered Trademarks of Model Engine Corp. of America
Registered U.S. Patent Office

Linking to this page is permissible, However no part may be reproduced without written permission from
MECOA -- P.O. Box 5 -- Sierra Madre, CA 91025 U.S.A.