Johnson Service Bulletin SB-960 - Fuel Pump Diaphragm Rupture

Issued June 21, 1963, this bulletin introduced a larger nylon inner spring support for certain Johnson fuel pumps to help prevent diaphragm damage. It also identifies symptoms of diaphragm failure and affected engines.

Johnson Motors Service Bulletin gray letterhead

June 21, 1963 #SB-960 - Fuel Pump

SUBJECT: PREVENT FUEL PUMP DIAPHRAGM RUPTURE BY USING PART #309944 SUPPORT

ENGINES AFFECTED

RX-10C thru 10R
RD-21 thru 24E
RDS-20 thru 24E
RK-24B thru 24E

V4-10 thru 11B
V4S-10 thru 14B
V4A-13 thru 14L

Fuel pump diaphragm rupture can be minimized on engines listed above by replacing the inner spring support with part #309944 - (see figure 1). Part #309944 support is now made of nylon and is considerably larger in diameter than part #304094 support - (compare figures A and B).

Factory exploded diagram of fuel pump assembly 377602 showing inner spring support 309944 and comparison figures A and B

Figure 1 - Part #377602 Fuel Pump Assembly.
Figures A and B - spring support comparison.

Do not attempt to replace the outer spring support with part #309944. The smaller support, part #304094, must be used with the outer spring due to space limitations in the pump housing.

OVER

Page 2

The following symptoms will usually result from a ruptured fuel pump diaphragm. Keep in mind, however, that even the smallest pin hole rupture in a pump diaphragm can cause these symptoms.

1 - Hard starting

2 - Rough idling

3 - Spark plug wet fouled
(bottom plug on 2 cylinder engines)
(number 4 plug on V-4 engines)

4 - Excessive fuel consumption

5 - Power loss at full throttle

Part #309944 support was first used on the following 1963 production engines: RX-11C, RD-25D, RDS-25D, RK-25D, V4S-15R and V4A-15E, and is now available from your parts distributor at the list price of $.05 each. Your standard parts discount applies.

Sincerely,

JOHNSON MOTORS

Robert Compton

Administrative Assistant

RC:eb

NOTE: Post on your RX-28 H.P., RD-25, 30 & 35 H.P., RD-40 H.P., RK-40 H.P. V4-50 H.P. and V4-75 H.P. indexes.

Historical parts reference

Part 309944 - larger nylon inner spring support; part 304094 - smaller outer spring support; part 377602 - fuel pump assembly. The two spring supports are not interchangeable in their respective positions.