Air Injection ?. . .

Hi there. I am a new member with a '79 KZ 650 SR. The bike is in as new condition and competely stock. It had been sat for a few years and came to me with some backfiring issues. The first thing I noticed were cracks on the coil bodies so those have been replaced with OE type EMGO coils. The backfiring decreased but persisted. Performing the Clymer manual test revealed that the switching valve is gone wrong.
While testing the bike with the hose plugged there was no backfiring but it would not run cleanly at steady throttle around 3000 rpm or so.Instead it would "flutter" and seem as if a lean condition had appeared. Strange because it will pull strongly during increasing throttle and idle right down like a streetbike should.
Initial impulse is to do a carb clean but I was told it has been done and it starts first kick every time and as previously mentioned idles just fine.
Any help as to what I'm missing would be appreciated.

eliminate the smog stuff and plug any related vacuam lines to see if that helps.
throw a set of plugs in there and a can ofsea foam in the tank to clean the carbs and put a few miles on there to see if that helps

.

Smog Block Off Plates
www.tpoparts.com
www.kzzone.com/billet.html