Topic: CB750 dreaded charging issue!

[Jcop.550]

I’ve been working on a 74 CB750 and finally got the bike to start right up and it’s idling/running nice until I go for a ride. About 20 mins into the ride the electronics shut down and eventually the bike cuts off and I’m left stranded.

Obviously, it’s a charging issue. I’ve searched high and low on about every forum thread a google search brings but cannot find a definite answer.

At idle, the bike stays around 12.3V and then drops around 11.3V when giving it some throttle so there’s something up with the charging system and I can’t figure it out. The stator reads .7 ohms, field coil is reading 7.8 ohms.

I have a new Ricks regulator/rectifier with a lithium battery wired with the mo.unit blue. Please confirm, but judging by the readings for the stator and field coil, it’s gotta be an issue with the reg/rec or my wiring.

Currently, I have 3 yellow reg/rec wires to 3 yellow stator wires, green and white reg/rec wires to green and white field coil wires, one green reg/rec wire to ground on m-unit (should this be grounded to the frame?), one red reg/rec wire to battery power on m-unit, and lastly, the black reg/rec wire to the AUX 1 output on the m-unit.

I spoke with Calj a while back about this (doesn’t look like he has an account anymore?) and he told me black to AUX 1. However, I’m also seeing in other forums black should be spliced to the ignition switch wire going to the LOCK input…

With that being said, I’m lost! Any help would be greatly appreciated.


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[scottly]

green and white reg/rec wires to green and white field coil wires, one green reg/rec wire to ground on m-unit (should this be grounded to the frame?),

Both the reg green wires and the field green wire need to be connected to ground, not just each other. The black reg wire needs to have 12V applied when the bike is running.

[bryanj]

Rather than when running when ignition turned on and the black wire needs to be at battery voltage within less than 0.5volt

[Jcop.550]

green and white reg/rec wires to green and white field coil wires, one green reg/rec wire to ground on m-unit (should this be grounded to the frame?),

Both the reg green wires and the field green wire need to be connected to ground, not just each other. The black reg wire needs to have 12V applied when the bike is running.

Ground the field coil green and reg/rec green separately? Or can they be connected with a spliced ground?


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[scottly]

You can connect the greens together and then to ground or ground them all separately; it doesn't matter as long as they are all grounded.

[scottly]

I spoke with Calj a while back about this (doesn’t look like he has an account anymore?) and he told me black to AUX 1. However, I’m also seeing in other forums black should be spliced to the ignition switch wire going to the LOCK input…


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The black reg wire should be connected to the ignition switch wire as the M-unit may have a voltage drop on the AUX 1 output, which will affect the voltage reference for the regulator. 

[Jcop.550]

I spoke with Calj a while back about this (doesn’t look like he has an account anymore?) and he told me black to AUX 1. However, I’m also seeing in other forums black should be spliced to the ignition switch wire going to the LOCK input…


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The black reg wire should be connected to the ignition switch wire as the M-unit may have a voltage drop on the AUX 1 output, which will affect the voltage reference for the regulator.

Switched everything up to how you said, grounded green wires and switched the reg/rec wire to LOCK on m-unit with the ignition switch. Voltage is reading 13.8 now at idle and no increase with higher RPMS.

Bad regulator rectifier? Poor ground?


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[bryanj]

13.8 is a good charge voltage and if it keeps that with lights on you have no problem

[Jcop.550]

13.8 is a good charge voltage and if it keeps that with lights on you have no problem

From my understanding, it’s supposed to increase to the mid 14s right? It’s staying around the same. Maybe a slight decrease with increased rpms.


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[bryanj]

Lithium batteries cant take high charging voltage and the figures you quote are for a "standard" lead acid battery and mechanical reg, as i asked before does it make the 13.8 WITH THE LIGHTS ON

[scottly]

I have a new Ricks regulator/rectifier with a lithium battery wired with the mo.unit blue.

The Ricks lithium specific regulator is set for 14V max, +/- .2v, IIRC, so you're probably OK.

[Jcop.550]

Lithium batteries cant take high charging voltage and the figures you quote are for a "standard" lead acid battery and mechanical reg, as i asked before does it make the 13.8 WITH THE LIGHTS ON

13.8 is with only the headlight off. All other lights are on. I unplugged the headlight the other day hoping that would solve the issue thinking the 52w LED bulb was drawing too much


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