August 25, 1961
Bulletin No. SB-862
Trouble shooting
SUBJECT: Overchoking on Cold starts;
75 h.p. V4S & V4SL-13 thru 13C
75 h.p. V4A & V4AL-13 thru 13F
Reports have been received to the effect that some 1961 V-75 engines failed to
start with the choke in automatic position due, apparently, to overchoking on cold
starts. Inspections and checks of such engines reveal adjustments may be in com-
plete accord with recommendations, yet indicate flooding.
This condition can be corrected by slightly advancing the carburetor's cam which
actuates the throttle roller. This means that the cam should be adjusted so the
roller touches the cam to the left of the index mark similar to that illustrated
in figure 2. This adjustment then causes the throttle to open a bit sooner than
the normal adjustment in which the cam's index mark falls in line with the center
of the cam roller. Note that this adjustment is the final one used in syn-
chronizing the distributor, or magneto, and carburetor (see SB-739 and SB-827)
except the cam's index mark is slightly advanced. The timing and synchronizing
procedure remains otherwise unchanged.
The actual amount of throttle advancement will vary from engine to engine. Make
the initial adjustment as illustrated in figures 2 and 3, and test it by running
the engine as follows:
1. Connect tachometer
2. Run engine to obtain a normal operating temperature.
3. With ENGINE IN NEUTRAL GEAR, open throttle as far as the neutral stop
and synchronizing linkage will permit.
a. Engine should run at a maximum of 2500 to 3500 rpm. If less
than 2500 rpm readjust cam and retest.
(NOTE: Under NO circumstances must the cam be advanced farther
than necessary to correct overchoking on cold starts. If the
problem is not corrected with the engine running between the
foregoing maximum neutral rpm range, check further for other
types of malfunction.)
With the foregoing adjustments, the engine will then run somewhere between 800 and
1200 rpm immediately after a cold start when up against the neutral stop. This
will enable the engine to carry through without flooding during the first few seconds
of operation.
The foregoing throttle cam adjustment is not necessary on all 1961 V-75 engines, and
is therefore to be made only on those engines on which the overchoking condition
exists. It does not supersede the normal adjustment specified in Service Bulletins
SB-739 and SB-827.
JOHNSON MOTORS
W. W. DeWees
Service Department
WWD:eb
NOTE: Post on your V-75 index.
(over)
