You may have heard of “Startus Interuptus”, its a term they use on the Wild Guzzi forum for failure to start.
It takes a very strong magnetic field to engage the Bosch or Valeo starters on our Guzzis. To produce this strong field there are two coils inside the solenoid not one as the schematic in the manual shows.
One of these coils draws 10 Amps but the other one will draw 40 Amps if you let it, yes a total of 50 Amps, 600 Watts at 12 Volts but only for a fraction of a second, as soon as the large solenoid contacts close they bypass the heavy current coil dropping the current back to 10 Amps.
Unfortunately the Guzzi wiring even on a new bike is not capable of providing the current the starter would like, there is too much resistance in the long path through the wiring and ignition switch.
The switch resistance gets higher over time as the grease gets hard, eventually it may get so high the solenoid just sits there overcome by mechanical load and all you hear is the dreaded relay click, the fuse often blows at this point just to confuse the isue.
What can you do about “Startus Interuptus”?
First of all clean the ignition switch and re-lube it with Vaseline (no fancy expensive grease please), make sure the Start relay is in good shape and the base is making good contact with the relay pins to provide as much current as possible to the solenoid.
The single best move you can make is bypass the ignition switch, feeding a wire direct from the battery via an in-line fuse straight to the start relay 30 contact (this happens to be a yellow wire on the more modern bikes like a Norge or Griso)
How do I know all this?
I have made a study of the Bosch and Valeo starter circuits.
To prove my theory I did a simple test on one of my California Guzzis, first of all I cleaned the ignition switch and all the connection points hoping to make the wiring as close to perfect as possible.
To measure the current I wired in a high current shunt with an Oscilloscope. (events happen too fast to measure with a normal ammeter).
I found it took 40 milliseconds between the instant I pressed Start and when the motor started to crank. The current peaked at about 30 Amps Next I bypassed the ignition switch with a wire from the battery to Start relay as I described above.
I found it now only took 20 milliseconds from pressing start to cranking, (twice as fast). The current inrush was also higher by about 10 Amps.
I also simulated what can happen when the solenoid is unable to pull in, the 15 Amp fuse popped in less than half a second.
Why did the bike get wired that way?
I don’t think the factory know about the second coil and they think the solenoid only draws 10 Amps (that’s what you would measure with a regular meter), how else can you explain the single coil on the schematics and the 15 Amp fuse, remember too, they only see brand new bikes with pristine wiring components. The trouble starts to show after a couple of years on the road.
What Guzzis can catch “Startus Interuptus”
Only the ones where the feed to the Start relay is fed through the ignition switch
All the later VIIs, Griso, Norge, Breva, I haven’t seen a V7 yet