Topic: Bypassing Speed Warning Unit

[raymond10078]

I just did this on my bike - this isn't theory.

In this other thread, I posted a schematic for the 76 CB750A change relay:

http://forums.sohc4.net/index.php?topic=112210.0

In that other thread, I promised to provide how to bypass the speed warning unit.  If you compare the 76 and 77/78 wiring diagrams, you'll note that the 76 doesn't have a speed warning unit.  That means that anytime the bike is in gear, the throttle is held slightly open - so raise the idle speed slightly when in gear.  The 77/78 bikes stop holding the throttle open above certain speeds.

Anyway - I and others have had some issues with the speed warning relay (which isn't a really after all, but a small circuit board).  If you can't (or don't want to hassle with trying to) figure out what is wrong, you can just bypass the speed warning unit by moving two wires around - changing your bike to 76 wiring for the idle solenoid control.

Here's what I did:

• Remove the left cover.
• Locate and disconnect both idle solenoid wires.
• Locate the four wires from the speed warning unit - and unplug all four.
• Locate the Black wire that was connected to one of the four speed warning unit wires.  It has a female plug.
• Connect the Brown/Red wire from the solenoid to Black wire in previous step.
• Connect the Black/Green wire from the solenoid to the Green/Black wire that plugs into the Change Relay.
• You're done!

I tested mine by turning the key on (set the kill switch to off), then moving in/out of neutral to Lo/Hi (or 1/2) while also putting a finger on the solenoid and feeling the click.  The other method is to unplug then touch the Black/Green wire from solenoid to the Change Relay wire with the bike in Neutral, then Lo, then Hi.  The click of the solenoid is audible then.

[salukispeed]

Thanks. I want to figure out what is wrong with my speed warning unit anyway but it will be nice to use it the rest of this season with it working partially..

[raymond10078]

FYI to all:  the manual isn't that clear (or is just plain wrong) - but the solenoid should operate as follows.

Solenoid OFF: A - B closed; B - C closed; A - C open.
Solenoid ON: A - B open; B - C closed; A - C closed.

On the 77/78 A bikes, the solenoid is energized when the bike is going below 20 km/h.  The 76 A bikes - the solenoid is energized anytime the bike is in gear.

The purpose of this system is to prevent exactly what you are experiencing - that is - to provide a stable idle regardless of the gear position (neutral, low or high).  On your bike, the idle has been set high - so that when the bike is put into gear, the idle remains high enough to keep running.  The downside is that a "lurch" that happens when putting the bike in gear.  The system allows a correctly tuned bike to be put into gear without much (or any) lurch at all.

In the end, you don't really need this system, it is a convenience feature.