Lower injectors work at the lower RPM's and the upper ones begin to work at around 8K if I'm not mistaken, all 8 work above 8K. Do they ever fail its an electrical part so yes they do fail. As for cleaning there is no reason you couldn't clean like any other injector.

 

Yes, many bikes have double injectors. However, your secondary injectors are still waiting for you to upgrade your bike.

 

So you're saying those are more than enough for the stock bike?

So if I understand ok. If the bike is running rough at idle it might be the lower injectors instead of the upper ones?

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Don't feel bad Aruek, I didn't get it either.

 

GSX-Rs have had 8-injectors since 1K5 and K6 600/750 models. It has more to do with optimising the fuel injection than the need for two sets of injectors. You could change the injector balance to 100% primaries and it would work just fine on a stock engine.