Gas Dripping Out of Airbox

I finally got my 81 KZ1000 M1 back together after almost two years. The bike ran great when disassembled, but now there's a problem. Carbs stored clean, dry and cool while rebuilding bike. Finished re-assembly last night and put gas in tank. Bike fired right up, and I ran it a couple of minutes. Ten minutes later, I re-started the bike, and now it ran rough on idle with a lot of popping in the exhaust. this morning when I started it, the exhaust popped/coughed a couple of time on choke, but ran smooth with no popping once I pushed the choke in. Then I noticed a small puddle of gas under the bike, and traced the source to the drain nipple under the airbox.

Anyone have any suggestions on where to start diagnosing? This has never happened before where a significant amount of gas was forced into the airbox. Is it most likely a carb problem after sitting dry for so long? I had re-built the carbs just before tear-down, and like I said, I did drain all gas out of the carbs before putting them on the storage rack.

Any suggestions would be greatly appreciated - hoping to do the Woodward Dream Cruise here in Detroit on Saturday, but right now, my hopes are not very high for that.

check ur valves, if an intake valve holds open while on compression stroke it will force fuel into the airbox.

Did you put the cams back in? Could be out of phase, off a tooth, etc...Got to be the intake valves letting gas back into the carb and subsequently the airbox.

Thanks, Guys. Actually, the engine has been untouched. I took the bike down to the bare frame, sandblasted and repainted. Brand new pro paint job on tank, covers, fenders, etc. Replaced shifter seals, new sprockets and chain, brakelines, steering bearings/races, swingarm bearings, fork seals, etc. But engine was not rebuilt, it just sat on the engine stand for awhile.

The bike only has 13K miles on it, so I didn't see the need for an engine re-build.

yeah, but a valve adjustment, or a stuck valve needing freed up from sitting may be to blame, even if the engine was untouched.

Are your carb overflow hoses routed into the airbox ?
Sticking carb float or float valve or spec of dirt under a float valve ???

My suggestion would be to clean the carbs and use Q tip soaked in carb cleaner on the float valve seats.

Well, a stuck valve could be the culprit. Best way to address that, or even verify? I had done the valve clearence adjustments to nominal shortly before tear-down, so I just assumed it was still good.

I am a complete novice with engines, so any guidance on checking to see if valves are moving freely would be appreciated, guys.

JR - I have removed the smog system and have a manual petcock, so all four nipples on carbs have caps on them. Am I missing something here? I don't have an overflow hose.

BTW, i learned the hard way not to try to start a bike that was filling the airbox with gas the hard way, i took rags and dried out the airbox as best i could, went to crank the bike and had a backfire throught the carbs, and FOOM!!! up in flames went the airbox!

just be careful give the fuel time to dry, use compressed air to verify the airbox is clear of fumes, and keep a liquid rated fire extinguisher at the ready, justin case.

I pulled the carbs to verify intake valves were operating freely and found little pools of gas in the carb holders for #2 and #3. Cleaned everything up real good and turned the engine by hand. Everything moves freely. Tore all the carbs down to check float movement and levels. Reassembled everything now, but I want to check the oil for contamination before I start the engine. I hope the oil is fine as it is brand new oil/filter.

jswag5, yep, when I thought I had cleaned the airbox good, I tilted it upside-down and another good-sized pool of gas ran down from the bottom of box, so thanks for the warning, it made me check thoroughly with airbox removed!

Floats move freely and the plungers on the float valves likewise. So, after I check the oil I'll start it up and see what happens. If it starts coughing and popping again on choke, I'll shut it down again. Will advise.

Thanks for your help, guys!!!

Capped overflow lines?????

Not a good idea! Those are there so that if the bike ends up on it's side or a float sticks the excess fuel drains out the overflows, not into the engine and airbox. I almost guarantee your original problem was a sticking float, a very common problem with any carb that's been dry for a long time. Easiest solution is to simply tap the offending float bowl with the butt of a screwdriver until fuel stops dribbling.

Either way, your oil is now probably contaminated with gas, so you must do an oil change.

Okay, now I'm a little confused. I was referring to the vacuum ports being all capped. My understanding is one was capped at the factory, two had the smog system attached, and the fourth was for the vacuum controlled petcock. There are no other fittings on my carbs. Since I removed the smog system and went to a manual petcock, that leaves all four capped.

Obviously, especially after what just happened, I would like to install the overflow tube. My only problem is I can't find where an overflow tube should go. My OEM service manual doesn't talk about one, the parts diagrams from kawasaki.com doesn't show one, and I don't have a clue where it should be. BTW, the carbs are Mikuni BS34's.

Appreciate your help, folks!