ok done a bit of research, it seems the engine in my 88-90 GSXR400 is a k707, am I right in thinking it should be a k709? Why would someone change the engine? does this mean to make it run, if I need a CDI I would have to buy one ofr a Bandit400 and not a GSXR or are they both the same? What is the difference between these two engines?

There were differences in the CDI over the years of Bandit 400 and GSX-R400 production. Here's a datasheet that somebody showed me recently:



I don't know if everything shown on this datasheet is absolutely correct but it does point out that there are differences to be aware of when replacing a Bandit 400 or a GSX-R400 CDI.

And don't forget that on the GSX-R400SP the carbs had a Throttle Position Sensor that was wired into the CDI to give better performance by actively controlling the spark advance during rapid throttle movements.

I'm working on a U.S. market 1993 GSF-400 and I've discovered that the bike's wiring harness has 7 wires to the CDI (4 wires in one plug and 3 wires in the other plug). All of the Bandit 400 Service Manual and the Bandit 400 Service Manual Supplement wiring diagrams only show 6 wires going to the CDI (4 wires in one plug and 2 in the other plug).