After asking for help on this board several months ago to troubleshoot its idle and fueling problems with my '93 C4, thought I'd share what I found.
I bought the bike new and it has run great up to a couple of years ago, when the transition from idle to the needles became rough. Stripped down the carbs, cleaned the jets, checked float-height and so on. It ran better, for a couple of months, when the idle then deteriorated; would not run well off the choke.
Got tired of pulling off the tank and airbox everytime I needed to get to the carbs, so I bought a free-standing auxilary fuel tank, hooked up a line to the fuel pump, for easy access and left the airbox off.
Drilled out the pilot needle covers, cleaned the orifices, adjusted the screws to 2.5 turns.
Still wouldn't idle, or run very well off the choke. Okay, must be an air leak, causing it to run lean.
Bought new clamps that seal the carbs to the manifold, and replaced the pilot jet o-rings. Pulled off the manifolds bolted to the head, smeared a layer of silicone across their surface. The bike would easily start and idled at a steady 1200 RPM, without the choke.
Great! It was fixed.
Wrong.
When I gave it even the smallest amount of throttle and opened the butterflies, it blubbered, spat raw gas out of the carbs and died. Still started and idled normally.
What the hell? Exotic theories emerged, ranging from ignition problems, to valve issues, to alignment of the planets.
Cut to the chase, my cousin, who has owned everything from a Norton Manx to his current Harleys, noticed that the carb throats were exposed.
"Does it have an airbox?"
I explained that for easy access to the carbs, I had not put it back on and was using the external gas tank. He suggested that we try replacing the airbox, and THAT WAS THE PROBLEM!!
Without the restriction of the airbox, the air/fuel mixture was screwed up, with the resultant blubbering.
After working on the thing for months, I felt pretty dumb.
The moral of the story is, the ZX-11 will not run without the sealed airbox system in place. After owning the bike for nearly 17 years and doing all of the wrenching on it, I should have known this.
If yours is displaying off-idle or other odd fueling problems, you may want to be sure that your airbox is in place and completely sealed.
Can't wait to ride it again.
Mike
