Overflowing out of second carb instead of starting

I'm currently resuscitating a 1980 Kawasaki KZ650 that I got from a friend as a project bike. It was stored for a little under 2 years with all the fuel drained and the carbs disconnected and worked before being stored. However, despite all my efforts and the help of the repair manual, I can't get it to start. I've replaced the coils and spark plugs and wired in a new relay for the coils direct from the battery so I'm getting a great spark. When I crank the starter with the plugs disconnected I can see the cylinders moving and the plugs sparking. It's hooked up to a battery tender so I know there's plenty of power. However, when I actually try and start the bike it turns over fine but refuses to start, and instead starts pissing fuel out of the second carb only. The plugs do not smell like fuel so I'm guessing that for some reason the fuel is flooding out of the second carb instead of getting to the cylinders. I'm guessing I've missed some critical component here that is not immediately obvious to me so I turn to you for help.

Do NOT try to start the bike while the battery is hooked up to a charger or another vehicle whose engine is running. Doing so can cook your bike's electronics.

When you try to start a cold KZ650 (assuming your bike has the stock 1980 petcock) put the petcock in "Prime"; do NOT touch the throttle, kill switch in "RUN"; key "ON". Use the kickstarter this time - do not pull in the clutch lever and give it several kicks.

I assume the fuel from carb #2 is coming from the overflow tube on the bottom of the carb? If so there are several things that can cause this. The 1980 KZ650 petcock will have 2 tubes. The larger one supplies fuel to the "T" fitting between carbs #2 & #3; the smaller diameter tube gooes to a vacuum fitting on carb #2. If your petcock is damaged fuel can flow from it into the vacuum port on the #2 carb. One easy way the check is to remove the vacuum tube from the carb and see if any fuel is in that tube from the petcock. There should be none. If there is, you need to rebuild or replace the petcock. If there is no fuel coming from the petcock the other ways a carb can leak fuel from the overflow are described below.

Fuel coming out of the overflow hose (the little hose on the bottom of the carb) is the common symptom of the 3 possible problems described below. Remember - NO SMOKING or other activities that could ignite the fuel while working on carbs!

The float valve is not sealing. This may be (and probably is) just a matter of some minor dirt in the float valve and is very simple to remedy and can be done with the carbs still on the bike. Turn off fuel; drain carb by loosening big brass screw near bottom; and remove the 4 little screws on the bottom of the carb bowl. This will enable you to remove the carb bowl. You will then see the float. If you carefully remove the float you will see a stubby little needle that mates with a brass orifice; together, these two pieces are the float valve. Assuming there is no obvious damage to the needle or seat, use a Q-tip and some carb cleaner to clean the seat of the orifice and the needle. Be careful not to bend the tang that is attached to the float. This tang is the piece that the bottom of the float valve needle rests upon, and it determines the fuel level in the bowl, so bending it will change the fuel level. With the float valve cleaned it should no longer leak. To prevent a re-occurrence a quality inline fuel filter should be installed between the fuel tank and carbs. If there was damage the needle and seat should be replaced as a set; they are available.

The brass overflow tube inside the carb bowl is damaged. When you remove the carb bowl you will see a brass tube attached inside and rising toward the top of the bowl. This is the overflow tube and it leads directly to the overflow nipple on the bottom of the carb. Normally, the fuel level within the bowl rises somewhat close to the top of this tube. If the tube becomes cracked or separates from the bottom of the carb bowl fuel will flow through it and out through the overflow hose. Checking the condition of the tube is very easy after you have removed the carb bowl from the carb. Simply hold the bowl level and fill it up near the top of the tube with water or alcohol and see if it leaks. A slight crack in the brass overflow tube can be difficult to find. You can connect a rubber tube to the overflow nipple, fill the bowl with water, put finger over the open end of the brass overflow tube and blow in the rubber end and look for bubbles. If it does the best remedy is to replace it although some folks have found creative ways to repair them.

The fuel level is set too high. This condition occurs when someone has bent the float tang as mentioned above. This condition can be checked using what is referred to as the "clear tube test." The test involves attaching one end of a clear piece of flexible tubing to the carb drain hole and holding the other end of the tube above the bowl/carb joint. When the fuel is turned on it should rise in the tube to a level 2.5 - 4.5 mm below the bowl/carb joint. If the fuel rises higher than that level it may run into the cylinders or over the upper end of the brass overflow inside the carb bowl (mentioned above) in which case it will run out the overflow hose. This condition is corrected by removing the float and gently bending the tang to raise the float valve needle position. Doing this may take several tries before achieving the desired fuel level.

Correcting each of these three conditions involves removing the carb bowl. This task can be made easier if a short screwdriver bit is used, and depending on which carb you are fixing a mirror may help you locate the screws on the bottom of the carb bowl. Also, it is not a bad idea to have a new carb bowl gasket available in case the old gasket is damaged while removing the carb bowl. Ed

Thanks a ton! Will try all that and report back!

Hi, hopefully you see this post. Thanks for your help so far- I tried what was suggested and ultimately just ended up removing the carbs entirely and dismantling them to do a full clean. I found that the check valves had been improperly reinstalled the last time they were cleaned, and the vents were covered for some reason. After cleaning the carbs and remedying these issues I reinstalled the carbs and fuel no longer leaks. Unfortunately, the bike STILL isn't starting. I'm getting a great spark, but the plugs don't smell like gas when I remove them, which suggests there's no gas getting to the cylinders. There's hoses attached to each of the junctions that connect the carbs to the cylinders which the previous owner appears to have plugged up-I can't find anything about them in the manual, are those somehow connected to this issue? I feel like I'm within striking distance here-the bike actually backfired once and momentarily sounded like it might start another time, but other than that it's just turning over. Thanks again!

Make sure your carburetor boots do not have a leak, make sure the clamps are on tight , otherwise the motor will be sucking in air instead of gas, and it wont ignite.

mopguy wrote: Make sure your carburetor boots do not have a leak, make sure the clamps are on tight , otherwise the motor will be sucking in air instead of gas, and it wont ignite.

I have double checked all the fittings and similar connections. Do you know what the hoses are intended to connect to?

This may help. Ed

Just wanted to say thanks for all the help to everybody who chipped in here. It ended up being a number of factors nobody could have guessed at really-mostly errors from the previous owner. The coils weren't wired to the points properly, and beyond that the points were all mucky as well. After doing some repair/cleaning/replacing, the bike starts just fine!