No. 229 February 20, 1942
SERVICE NOTES FOR ALL MODEL “M” LINKERT CARBURETORS ON HARLEY-DAVIDSON MOTORCYCLES
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 engine dies from leanness.
HOW TO REMOVE THE CRUST
- Back off the throttle lever stop screw so that the throttle disc closes tightly. With a sharp pointed tool like a sharp pen knife or scriber, scratch a line deeply on the closed throttle disc and also on the throttle barrel so that the lines on the disc and on the barrel meet. These lines should “jibe up” again 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.
- Scrape out the caking or crust in the throttle barrel with a scraper or knife, being sure not to cut into the metal.
- Clean up the throttle disc by rubbing 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.
- Clean out the idle holes in the throttle barrel next to the disc with the proper size drills of clean-up tool set described on last page of this bulletin. See following list for proper sizes for both holes for all models of carburetors.
|Model (Stamped in top of Carb. Body)||Carb. Size||Venturi Size||Small Idle Hole Nearest Manifold Flange (Drill Size)||Idle Hole Farthest From Manifold Flange (Drill Size)||Slot Width|
|(Model numbers followed by letter “F” or “F1″ or “LF” apply only to carburetors used on California Highway Patrol motors.)|
- Clean out the slot of all 1″ and 1 1/4″ carburetors by inserting the tool with the .009″ blade (this tool has plain handle) through the slot between the two idle holes. Use the tool with .0155″ blade (this tool has two rings around its handle) to clean out the slot in M25, M35, M35F, and M35S 1 1/2″ carburetors. Use the tool with .020″ blade (this tool has Springs around its handle) to clean the slot in M75 and M75F 1 1/2″ carburetors.
- Clean out the idle channels with the #42 drill. When cleaning vertical idle channel do not completely bottom drill as doing so may damage the low speed needle seat.
- Clean out the low speed (idle) needle valve seat hole with the proper drill size. All earlier 1 1/4″ and 1 1/2″ “M” carburetors are cleaned with the #53L drill. Later Model M-35, M-35S, M-75 and M-75F, 1 1/2″ carburetors, have a smaller channel above the seat hole and for these use the #53L #2 drill which has a smaller handle, (this tool has two rings around its handle). All model 1″ carburetors are cleaned with the #56L drill.
- Blow out all channels and holes with compressed air and wash all parts in gasoline.
- Re-assemble the parts, being surethe lift lever spring seat or 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, otherwise carburetor cannot be adjusted for satisfactory engine idling.Be sure the throttle disc is assembled in the barrel properly and closes off tight. Have the correct side of disc up or toward the flange and with the lines you scratched lining up with each other 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.
ATTENTION TO MODEL “M”
LINKERT CARBURETOR BOWLS
- 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 so 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.
- 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. The 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 of bowl. 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.
- Check float level, and if necessary, re-set to 1/4″. 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 disassembling 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 screw driver 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.
- The bowl drain plug now being used in the Model “M” carburetors can be removed for a quick flushing of the bowl. Before removing this plug turn off the gasoline at the tanks. Be sure to pull up this screw tight when replacing.
ADJUSTING CARBURETOR ON ENGINE
- In adjusting the carburetor, set the low speed needle for smooth idling, and set throttle lever stop screw for desired idling speed.
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 set for reasonably fast idling.
Average high speed needle adjustment for best engine performance is as follows: All Side by Side Valve engine carburetors – about 1 1/2 turns open; all O.H.V. engine carburetors – Model M-25 about 1-1/4 turns open; Models M-35 and M-36 about 1-1/8 turns open; Models M-45 and M-75 about 1-3/4. turns open. It is advisable to set high speed adjustment slightly rich rather than as lean as possible as a lean high speed mixture causes overheating.
CARBURETOR CLEAN-UP TOOLS
These tools are for hand cleaning only. Do not use in power or hand drill, A complete kit including 12 tools is covered by Part No. 12012-58, list price $6.00. If you already have a set of clean-up tools that originally included ten tools, you will need only two extra tools to make your kit complete, part No. 12012-38L and 12012-58M. If you have an earlier kit that originally included only eight tools you will need to complete it the two extra tools just mentioned and also two additional tools, part Ho. 12012-38J and 12012-58K. Extra tools are 50c list each.
(All part numbers mentioned in this arctile are H-D part numbers.)