153 – Service Information Applying to Model “M” Linkert Carburetors On Motorcycles

SERVICE INFORMATION APPLYING TO MODEL “M” LINKERT CARBURETORS ON MOTORCYCLES

M-341, M-341-1, M-342, M-343, M-344, M-344A, M-441, M-541, M-641. M-641-1, M642, M-644, M-741, M-741-1,
M-841R, M-841L, M-Bonn., M-Bonn., M-Bonn.-1.

(All models have the model number stamped on the pad on top of the carburetor.)

These notes apply to carburetors which have been in service for some time and have become dirty, full of “crust” in the throttle barrel, and are found to be difficult to get adjusted properly. Usually the effect of excessive dirt or “crust” formation in the carburetor throttle barrel, around the throttle disc, and in the fuel mixture passageways, is to cause the carburetor to have a lean spot off idle. This “crust” should be removed, particularly when a lean spot comes in at speeds off idle up to 30 M.P.H. with the low speed (idle) adjustment set properly for idling. The idle adjustment should not be set to the very lean side when checking this point, but to a point about five to ten notches rich from the setting where the motor dies from leanness.

HOW TO REMOVE THE CRUST

1. Back off the throttle lever stop screw so that the throttle disc closes tightly. With a sharp pointed tool like a sharp pen knoif or scriber, scratch a line deeply on a closed throttle disc on both sides of the throttle shaft and against the shaft. These lines should “jibe up” again with the shaft when you replace the disc. Remove the throttle lever, throttle disc and shaft, the idle hole body plug next to the idle holes in the throttle barrel, the body plugs in the carburetor flange and carburetor body idle channels, and the low speed (idle) lift lever and needle valve assembly. Also remove the venturi and nozzle.
2. Scrape out the caking or “crust” in the throttle barrel with a scraper or knife, being sure not to cut into the metal. “Crust” or caking can be removed easily with a rag moistened in acetone.
3. Clean up the throttle disc by rubb1n~ it on both sides on emery cloth on a flat plate and clean the edge of the disc all around, being careful not to round the corners or cut into the metal. The disc can also be cleaned with acetone. See note 2.
4. Clean out the idle holes in the throttle barrel next to the disc with the proper size drills. See list for proper sizes for both holes for all models of carburetors.

Clean out the slot of all models by inserting the tool with the proper thickness Slot Tool – see List above for slot width. The .008″ Slot Tool has no ring around handle. The .014″ Slot Tool (to be used in the .015″ Slot) has 2 rings around the
handle. The .018″ Slot Tool ( to be used in the .020″ Slot) has 3 rings around the handle.

6. Clean out the idle channels with the #43 drill. When cleaning vertical idle channel do not completely bottom drill as doing so may damage the low speed needle seat.

7. Clean out the low speed (idle) needle valve seat hole with the proper drill size. All l¼” carburetors are cleaned out with the #53L#2 L.S.N.V. Seat Hole Tool. This tool has 2 rings around the handle. 1″ Carburetors are cleaned out with the #55-L L.S.N.V. sent Hole Tool.
8. Blow out all channels and holes with compressed air and wash all parts in gasoline.
9. Re-assemble the parts, being sure the lift lever spring seat (washer) is between the spring and carburetor body when assembling the low speed lift lever and needle valve assembly back into place. This spring seat or washer limits the air bleed to the idle system and must be in place: otherwlse carburetor cannot be adjusted for satisfactory motor idling. There are two kinds of seat washers, a thick one and a thin one. Be sure to replace the one as assembled at the factory.
   
   Be sure the throttle disc is assembled in the barrel properly and closes off tight. Have the correct aide of the disc up or toward the flange and with the lines you scratched lining up with the throttle shaft exactly. Push up the shaft collar (on the throttle shaft) firmly against the body before tightening the throttle disc screws. The throttle lever should be clamped to the shaft with the disc wide open and with the throttle lever wide open stop against the body lug and with wear take-up spring between the throttle lever and bearing.
10. If the carburetor bowl continually leaks or runs over, remove it from the carburetor body and first remove all dirt by cleaning it out with gasoline and compressed air. Hold the bowl Up-side-down to that the float valve closes and suck on the bottom of the float valve seat. The valve and seat should hold this suction. If the valve and seat leak after repeated testing, replace with a new float valve and float valve seat.
11. If the float is damaged or “logged” replace with a new float. Remove the old float by cutting the seal around the float screw which fastens the float to the float lever. This seal can be cut with a pocket knife. Remove the float screw and assemble the new float to the lever. This should be done with the float valve, float valve lever, float hinge pin and screws, float valve seat and gasket assembled in the bowl. Before tightening float screw securely, adjust as follows: Looking down on bowl with gasoline inlet side away from you, pull float toward you to the limit of slot in float lever and about 1/16″ to left of center line . This provides necessary body clearance. Tighten the float screw and cement the top of the float screw to the float with Dupont Household Cement, or with a mixture of celluloid dissolved in acetone, or with thick shellac . When the cement has dried thoroughly, check the float height and adjust as explained in 12.
12. Check float level, and if necessary, reset to 1/4″ (M-741 and M-741-1 reset to 7/16″.) Measure directly opposite float lever with bowl held up-side-down (top of float to top of bowl.) When re-adjusting Linkert carburetor float, do not attempt to do so by simply bending float lever upward in some manner, without dis-assembling from bowl. Re-adjusting in this manner bends and spreads the fingers between which the head of float needle fits, and thus develops lost motion between float and needle. Float and lever assembly should be removed from bowl, and lever then bent as required.
    
    Before re-assembling, see that needle head is a good free fit between lever fingers with not more than approximately .003″ play. This clearance can also be checked after the lever is assembled in bowl, by carefully placing a small screwdriver or a small rod against the valve head in such a position that it will hold the valve firmly against the seat and yet not bind the lever. Moving the lever up and down will then show the amount of actual clearance between the valve head and fingers. If this clearance is excessive, the float mechanism will not feed properly. After assembling note that float is approximately square with top of bowl.
13. The bowl drain plug now being used in the model “M” carburetors can be removed for quick flushing of the bowl. Before removing this plug, turn off the gas at the tanks. Be sure to pull this screw up tightly when replacing.
    
    ADJUSTING CARBURETOR ON MOTOR
14. The low speed needle is the adjusting needle to the right (looking at the air intake end.) If low speed needle is so far out of adjustment that motor does not start readily, screw it down until needle knurl bottoms, then unscrew it about three to four turns. After starting the engine, unscrew it further if too lean or turn it down if too rich. After motor has “warmed up” set low speed needle for smooth idling. Be sure choke is wide open before making idle mixture adjustments. Too rich an idle adjustment will cause excessive rolling, and too lean an adjustment will result in idle dying or very rough and unsteady operation. Starting and all-around carburetion are better with low speed adjustment slightly rich rather than as lean as it can be made and with throttle stop screw screw set for reasonable fast idling.
    
    High Speed adjustment is made by setting the High Speed Adjusting Needle (Left Hand adjustment looking at the Air Intake) to the proper setting. Good average High Speed Settings are as follows:

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