What can cause gas leaking into the air box on a Kawasaki ZR-7?

Glad to hear hope it wasn't anything serious.

Several things could be wrong. First, the fuel petcock (valve) at the bottom of the gas tank should be turned off when the bike is not being ridden. Also, it is possible the valve may not be fully shutting off the gas. This can allow the carb to overflow and leak gas. A stuck open or punctured float in the carb bowl can cause overflow. The float should be light as a feather and have nothing inside it but air. Is the carb securely mounted?

Check for cracked fuel hose or bad connections at the tank and carb. Is the fuel valve body leaking gas where it mounts to the tank? Heck, with the bike being 36 years old the tank may be leaking at a weld or due to rust through. I wish I could work on your bike. The older bikes are more fun to work on than the newer bikes. Post a reply and let me know what you find.

Hi
Thats the float valve seals not shutting off, did you clean them & set the float heights?
The overflows from the carb bottoms must also be blocked for the fuel to fill up the carbs which then leaks into the air filter
Check also that the fuel tap turns off when bike is not running

Ride Safe
Bike-Doc

iv'e found that when you have a problem at a certain rpm in any gear it's a spark plug ploblem. you can either take out your plugs and make sure they're all gapped the same, or install new ones making sure they're all gapped the same before you put them in.

the gas tap has a diaphram and plunger to turn off the fuel when the engine is stopped, this may be dirty, worn or the diaphram gone hard. If dirt has got into the carbs it must have gone through the gas tap.
clean it or get a gas tap rebuild kit

Check you main jets ccccccthey could need a good wiring through with needle wire cleaners or try running it without any air cleaner unit .If it runs well then could be an air filter problem.

Check gas tank,lines,gas filter,fuel pump, drain carb. bowls to see if any thing comes out, if fuel goes in the carbs BUT it does not run right , the carbs. need to be cleaned and also synchronized,BUT, if it's your injectors and you do not have carbs. the injectors need to be cleaned.Is your air filter stopped up?

make sure that all of your little pendulium's that block the gas line when floats are raised are properly aligned in the chamber

i'd start with removing the carbs and giving them a thorough cleaning as when bikes sit for so long, the carbs begin to get gummy/varnished from the old gas.

check for blocked holes in the pilot jet & main jet and look for "hard & dried up" gas in passages. be careful of the float bowl gasket as to not tear it or you will need a replacement.

If you did not completely disassemble the carb and remove all jets/emulsion tubes/needle valves then you did not clean the carb adequately. You could try adding either Seafoam, the Yamaha CARB-CL-EAN-ER, or Techron fuel system cleaner in an auxiliary gas tank and running the engine for a short while to ensure the mix gets into all the nooks and crannies. Let it sit for a couple hours to do the work, then drain out the float bowl, hook up the bike's gas tank and see what happens. Otherwise you need to remove, strip, clean, reassemble, and reinstall the carb.