tachometer
It was a long time ago, don't exactly remember the fine details but here is a schem that is similar. The difference was I used an LM395 for the trigger input, the base tied to the tap coil around the spark wire.
Again, this was for a lawn mower so perhaps there was less noise. Definitly less energy in the spark.
You say yours is not working, please post your schem and maybe we can figure it out. The timing adjustments can be tricky for pulse type sensing but as long as your input is low when the timer wants to reset you should be ok..