Johnson Service Bulletin SB-961 - Rubber Tipped Carburetor Float Valve

Issued June 20, 1963. Original two-page Johnson Motors bulletin documenting rubber-tipped carburetor float valves, engine applications, and proper float-level adjustment.

Johnson Motors gray factory service bulletin header
SB-# 961 Carburetion
June 20, 1963
SUBJECT: RUBBER TIPPED CARBURETOR FLOAT VALVE.
Rubber tipped carburetor float valves are now being used on all production engines - see illustration, figure 1.
Original factory figure 1
The rubber tip on the new carburetor float valve acts to cushion the wearing action of valve and seat. Thus, valve life is increased, seat wear is not noticeable and carburetor flooding due to valve malfunction is greatly reduced.
The following engines use the indicated rubber tipped float valve assemblies:
JW-10 thru 17S V4-10 thru 11B V4S-10 and up Use assembly #379312 V4A-13 and up
CD-10 and up AD-10 thru 12 QD-15 and up Use assembly #379313 FD-10 and up FDE-10 thru 12
JW-18R and up RX-10C and up RD-10 and up RDE-16 thru 19C Use assembly #378895 RDS-20 and up RK-24 and up
QD-10 thru 14A Steel needle only - Use assembly #375654
List prices of the new carburetor float valve assemblies are as follows:
378895 - $1.35 379312 - $1.35 379313 - $1.35
Your standard parts discount applies - order only from your Parts Distributor.
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Page 2
PROPER FLOAT LEVEL ADJUSTMENT:
When installing a new carburetor float valve assembly, it is extremely important that float level be checked and accurately adjusted as described here. If the float level is too high, fuel will start flowing through the high speed nozzle prematurely, delivering more fuel to the engine for a given running condition than it should (RICH MIXTURE). On the other hand, if the float level is too low, fuel will start flowing through the high speed nozzle later than it should and will in this instance deliver less than the required amount of fuel for a given running condition (LEAN MIXTURE).
Original factory figure 2Original factory figure 3Original factory figure 4
Figure 2
Figure 3 - Proper Adjustment
Figure 4 - Improper Adjustment
Carburetor floats for all engines listed on the preceding page (except QD-10 thru 14A) are adjusted with the carburetor air horn (float bowl cover) in an inverted position, so that the float is parallel with the gasket surface of the casting - see figure 2. The float arm must also be straight as indicated in figure 3. In event that float arm is bent or twisted, as shown in figure 4, inaccurate fuel level will result.
To adjust the float on QD-10 thru 14A carburetors - proceed as follows. Remove and invert the float bowl. Top of float will be parallel to gasket surface of float bowl casting if float adjustment is correct. To adjust float height, bend small tang at end of float arm that slips over groove in check valve needle.
Always install a new float bowl gasket after checking the float level and stress cleanliness during all carburetor work.
Sincerely, JOHNSON MOTORS R. Compton Administrative Assistant
RC:eb NOTE: Post on all indexes.