Questionhello i have a 78 cb750f that i have modified extensevely but the engine is pretty much stock other than a dyna s ignition and dyna 3 ohm coils and a integrated rec/reg. The bike is kick start only and only has a head light and a led tail/brake light. The issue i am having is that when the bike is started up first thing when cold it charges great at about 14.5 volts around 2 grand i would say.But once i take it around a 5 min ride and check again its only charging around 12.3 or so. I have tried everything i put a diff rec/reg,a rotor off a charging bike and a stator/feild coil of a charging bike that i was told was charging i should say, ive checked all the wiring and its all good i am at a total loss here i would certainly appreciate any help thanks!!
AnswerMike.. from the www.sohc.net site:
Testing of the excited-field coil charging systems:
Three-phase charging system inspection and maintenance for all pre-79 SOHC 4-
CYLINDER motorcycles.
I. Initial inspection.
A. Charging system fuse check
1. If open replace.
2. If shorts again search for short circuit.
II. Full load test. (Determines battery condition).
A. Turn ignition and high beam on, while bike is not running.
B. Test battery voltage.
C. Voltage bellow 10.5V means battery needs service.
III. Charging the battery.
A. If specific gravity of any cell is less than 1.230 battery has low charge.
B. If sediments in battery are touching bottom of any plates, replace the
battery.
C. If specific gravity varies, more than .050 then replace battery.
D. If fluid level is low, add distilled water only. Do not add too much, as
level may rise even more while charging.
E. Charge the battery at no more than 10 percent of its amp-hour rating.
F. If battery temperature is more than 113 degrees F, allow it to cool
then resume charging.
G. If specific gravity of any cell will not charge above 1.230, then replace
the battery.
H. Put the fully charge battery back in the bike and do the full load test
again. A running RPM test cannot be done unless you have a fullycharged
battery. If the voltage is above 12V then you can do the RPM
test.
I. Start the engine and lock the throttle, when the RPM is above 4000. If
the voltage is between 14V and 15V, the system is fine and the battery
was to blame. If not you have more work to do.
IV. If @ 4000 RPM the voltage was below 14V…
A. Check for problems.
1. Corroded, loose, or mismatched wires. i.e. orange and green
wire plugged in to each other.
2. Modified or non-stock systems.
3. Visibly damaged wire insulation.
B. Do a system resistance test analysis.
*. NOTE 0 resistance = good wire.
*. NOTE infinite resistance while grounded to frame = good
insulation. Coils will automatically have resistance.
C. Resistance testing of regulator wires.
1. While the bike is not running, disconnect (-) battery lead and
Black regulator wire. Check for 0 resistance between (-)
battery wire and Black regulator wire.
2. Disconnect all regulator leads.
a. Test for resistance between I and F poles. 0 resistance is
good. If greater than 0, clean the regulator points.
b. Test for resistance between the white wire and ground.
Resistance between 4 and 8 ohms means the field coil is
good.
V. Testing the stator yellow leads.
A. Test wires 1 and 2, 1 and 3, 3 and 2 for ohm readings. Less than 1
ohm means the circuit is good. Greater than 1 ohm means poor
connection. Infinite resistance means that the coil has an open circuit
or possibly a bad lead.
B. NOTE. For GL1000 you need to disconnect/remove the permanent
magnet rotor before continuing. Set tester to insulation resistance
and calibrate it to 0 to perform a wire insulation test on the stator.
Ground the negative test lead and touch the other lead to each of the
three stator wires. If the resistance is infinite then the coil is ok. If
not then the coil is shorted to ground.
C. Test the three stator wires in the harness of the motorcycle. First,
disconnect the rectifier. Set the tester to resistance. 0 resistance
means all three wires are fine. Greater than 0 means the wire is bad.
D. Check the wires for bad insulation. Connect the black tester lead to
ground. Each wire should have infinite resistance. Greater than
infinite resistance means the wire has bad insulation.
VI. Check the five leads on the rectifier.
A. To perform a forward bias test, first connect the red tester lead to the
green ground lead.
B. With the black tester lead, test all three yellow wires.
C. Resistance must fall between 5 and 40 ohms.
D. To perform a reverse bias test, connect the black tester lead to the
green ground lead.
E. With the red tester lead, test all three yellow wires.
F. Resistance must be greater than 2000 ohms.
G. Connect the black tester wire to the red and white rectifier lead.
H. With the red test lead, test all three yellow wires.
I. All three must have between 5 and 40 ohms.
J. Connect the red test wire to the red and white rectifier lead.
K. Test all three yellow wires with the black tester lead.
L. Resistance must be greater than 2000 ohms.
VII. Testing the harness plugs and leads.
A. Test each of the plug wires in the circuit for o resistance.
B. While the battery and rectifier are disconnected test the red and white
harness rectifier wire to the (+) battery lead for 0 resistance.
VIII. Regulator bench test.
A. Remove regulator cover.
B. First, check the core gap to be sure it is between .6 and 1mm.
C. Next check the points gap to be sure it is between .3 and .6mm.
D. Clean the points with contact cleaner.
E. Note the 350F point’s gap is not adjustable.
F. Test the regulator leads by first placing paper on both sides of the
points contacts.
G. Test resistance between I and F, then I and E terminals. Check you
manual for model specific resistance readings.
H. Test for 0 resistance at regulator points connections.
I. While the points, contact is in the upper position test between I and
F.
J. While in the lower position test between F and E.
K. Note. Do not file the points or they will quickly pit when used again.
IX. Perform RPM test again. Be sure all components meet specs before going
forward from here.
A. Reconnect all components but leave the regulator cover off.
B. Start the bike and lock the throttle at 4000 RPM.
C. The voltage should read between 14V and 15V.
D. If voltage is low unlock the adjuster screw nut and turn the IN. NOTE
do not run the screw into the coil winding or short the screw to
something else with the screwdriver.
E. If voltage is high, adjust the screw OUT.
F. For the 350F bend the arm up for and increase in voltage or down to
decrease.
G. Replace the cover and test the voltage again, as the cover can have an
affect on the field of the coil.
H. GO FOR A RIDE!
Possible other considerations are with the upgraded reg-rect unit that the battery is being held to closer to battery voltage when the bike has refilled the charge after initial start-up. A fully charged battery is generally said to have about 13.2 volts. Charging a fully charged battery at 14.5 volts could be counter-productive over time. A halogen headlight current draw will offset the "gain" of the LED tail light and lack of running lights and winkers.
Make sure that the reg-rect is rated for use with a field coil type of charging system.
Bill Silver
