What was the reason for using these? I assume that volumetric throughtput of main injectors is simply too large for engine of small displacement.
Your guess is correct, these ZX-6R secondary injectors have the exact volumetric profile that a high-revving 100cc cylinder needs.
You have to find a Goldilocks solution with injectors: not too big, not too small. Too big and the injection Pulse Width at idle becomes impossible to tune properly, and too small means you run out of delivery capacity before the engine reaches its redline speed.
When I first decided to try them I had no idea if they were a match for the GSF400, but they seemed like they might be a good bet and, as mentioned, they were for sale on Ebay at dirt cheap prices so it was worth taking the chance.
The gamble turned out good, these ZX-6R secondary injectors tested at 160cc per minute under 43.5 psi (held open, full flow). In actual use most fuel injectors cannot be constantly held open, in fact they are intended to have a maximum "duty cycle" (which is the ratio of "on" vs. "off") of about 80% to 85%. So by doing the math to account for that: 160cc per minute constant-flow test result reduced by 20% to approximate the normal maximum 80% duty cycle I got a 128cc per minute "real world" number which was perfect for the GSF400.
