1972 Honda CB750 K2 - Won't Start

[Jrperida]

Recently got this 1972 Honda CB750 K2 as a restoration project. Previous owner stated that it hasn't been running for 2 years or so. Compression was good, just about 150-160psi and got a multimeter to check the battery and the ignition coils. They're both good but still can't seem to start or even get a spark off the plugs. The contact breaker points seems to be okay, no signs of wear or tear. I was thinking maybe there was a break in the circuit, perhaps the engine stop switch (Kill Switch) need to be replaced. I can't seem to really diagnose the situation. Any advice would really help.

Thanks

 

[vandito.cb]

open the switch up and check for continuity between the switched power and the power out that's feeding the coils.

should be black and black/white wires you're looking for.

 

[irk miller]

Are you hitting the start button and it's turning over, just won't fire?

 

[Jrperida]

In all honesty nothing really happens when I hit the electric start button. The only feed back I'm getting is that the 4 indicator lights on the dash lights up when I turn the key.

I'm fairly new to this but what exactly do you mean by turning over?

 

[omgwtfbbq!]

Turning over means the starter is turning the engine but there is no ignition (the engine won't run by itself). If hitting the starter button does nothing you either:

1. Have a faulty starter button, which you can check with a multimeter, just unplug the right control and see if there is continuity on the appropriate wires (the diagrams are posted on this site and can be found with a google search).
2. Have a bad starter relay, you can check this by using a pair of pliers to short the two terminals on the relay. If the starter kicks you need a new relay.
3. Have a dead battery, it's amps that count, not volts, a battery that reads 12.4V can still be useless for a bike. Get a new battery or take yours to an auto parts store and they can test it (usually for free).

Batteries go bad more often than relays, which go bad more often than starter buttons. But I always like to check the easiest things first.

 

[Jrperida]

I couldn't help but notice on the service manual it indicates that the starter relay is right where the magnetic switch(solenoid) is. Are they the same thing or completely separate part?

 

[omgwtfbbq!]

Relays are magnetic switches. So I'm gonna say yes, same part. I have a DOHC so I'm less familiar with the SOHC stuff though.

 

[irk miller]

Yep. Same part. Mounted on the battery box. Direct wired from the positive on the battery and the reg rec. Two wires to the starter button.

 

[Jrperida]

So apparently I did need a new battery. The engine finally turns but doesn't fire up. I notice for my ignition switch the bike will only start when the key is on the 1st position rather than the 2nd. It actually turns off when i turn it to the 2nd position. I don't suppose that's normal?

 

[adventurco]

Second position on most motorcycles is a "park" feature. No power to the ignition, just tail/headlights. AKA useless for all intensive purposes.


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