Electronics 2000

Hi guys, I'm fairly new to electronics, I play with domestic wiring and vehicle wiring but now I'm expanding my knowledge for a project I am doing, I'm starting bike racing next year and want to build myself an automatic shifter for my bike. All it does is when I push on the gear change lever, that activates a switch which sets off a timer relay which earths out the signal to the coils for around 0.04s and 0.1 seconds, I need to kill both signal feeds (1 to each coil) so need a diode on each feed to the relay to stop them crossing over and sparking the wrong boil, I realise there's hundreds of diodes out there so I need one that will work with a 12v pulse so it will need to be a fast acting one .

Also what 12v timers are out there that will time for hundredths of a second? I got one off eBay that does 0.3 of a second but that's still too slow really.. I realise this may be in depth for a first post, any help would be greatly appreciated, thanks, Joe

If this is any help, this is a rough diagram of what I want to do, I didn't to cut the live feed to the ignition coils incase I get a back emf going into the relay

What will the effect be on the CDI unit of grounding it out? Is there a way of just switching this out instead?
Mechanical relays will probably not offer good timing in the region you want, they take time to operate. Maybe some sort of opto relay switching power or pulse off to the CDI ignition module?
I thought a CDI just went directly to the spark plugs, no coil. Just a capacitor discharge like you get in a camera flash gun.
If so then I don't think a diode or similar device will be any use as you have drawn them switching EHT (extra high tention - into the 1000s of volts!!)

I've been thinking about this, I was thinking of switching the pickup which sends the signal to the cdI in the first place, I need to find a timer of some sort now just don't know where to start lol you're right about the relays being slow because of the coil energising and energizing, thanks for your reply

Pauldf wrote: I thought a CDI just went directly to the spark plugs, no coil. Just a capacitor discharge like you get in a camera flash gun.

Nope. You still need a coil to drive the sparkplugs, even with a CDI. You can't magically get 20kV or so just by discharging a capacitor.

Camera flash guns have a small (and rather primitive) switched power supply to make the HT for the flash tube, which is "only" 300V or so anyway. The high pitched whine you can hear from some (older) flash guns after they fire is the SMPS recharging the flash capacitor.
Incidentally, firing a flash tube involves a circuit not dissimilar to a CDI sparkplug ignition circuit, only the coil is a lot smaller.