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Discussion Starter · #1 ·
Hey everyone, whats up? I am new to the forum, hope someone could help me out. My name is Tom and I have a 2001 ZX9R with about 9,000 miles. The bike is well maintained. I've been having some carburetor problems with my bike lately. During idle the engine runs very rich. Unless I am racing the engine, the #2 carburetor loads up with fuel causing the bike to shut off. First I pulled the spark plugs to determine which cylinder was flooding, I noticed that the #2 piston was wet with fuel and full of carbon. I removed the intake manifold to get a better view of the main needle in the top of the carburetor. During idle I could see the fuel pouring into the top of the #2 carburetor. I pulled the #2 carburetor bowl off to check the float and valve, everything looks fine. Since the float valve seat is part of the carburetor housing the only thing I was able to do was clean it. I even cleaned the main jet and checked the main needle assembly. The #2 carburetor was still flooding into the cylinder. I then started swapping parts with the #1 carburetor to try to narrow down the problem. I changed the float, float valve, main jet and main needle assembly. No matter which part I changed, the #2 carburetor still flooded the cylinder. I called some local shops but received some very expensive quotes which consisted of the purchase of a new carburetor. I am stuck and could use any advice.
 

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If your bike always performed good until recently, your carbs are surely OK. Carbs do not really "break" and getting new ones is really overkill (except for your dealer, of course). If I was you, I would never go to the shops that suggest buying new carbs.

Have you made some recent modifications or have you (or someone else) worked into the carbs recently just before this problem appears? I'm no carb expert but common sense and logic can sometimes help...
 

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Discussion Starter · #3 ·
Early in the spring I started experiencing vapor lock on my bike. I figured I would do some routine maintenance so I changed the spark plugs, fuel filter and air filter. Over the summer my bike sat in the garage for about 1 month. Shortly after getting back on it I started experiencing this fuel problem. I never linked the two problems together until recently.
 

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Hi Tom,
I have a 1989 ZX-10 with the same carburetor issue on all four carbs. No matter what I change or adjust, fuel just pours out of what I believe is the overflow port on the air box side of the carburetors. I notice that the date of your string is from about a year ago. I have been researching this for weeks. Have you solved your #2 carb issue yet?
 

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If it actually is a carb problem, it has to be something that was not swapped out since swapping parts did not move the problem to another cylinder. This would lead me to suspect the float needle seat as the culprit. On another tack, the fuel pump(s) are supposed to shut off when a certain amount of pressure is in the system. If this is not happening as it should, too much pressure may be overwhelming the float needle/seat enough for fuel to flow through the carb as you describe. Or possibly something else is preventing the float from functioning properly such as the pivot pin somehow not allowing the float to seat the needle.
 

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Carbs

You need a carb clean. Complete carb clean not one of those pull the bowls off and pray cleaner in them. THey need to soak for an hour be dissembled cleaned and put back together. Normally runs $250 for this service in most shops. Now a days finding a shop that will clean carbs is hard. Yoou can do it yourself, have patience its going to take you 2-3 times on that set to get them right.
 

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Same Problem ZX11

I had a bike shop for several years and recently took on a project for a buddy to fix his Carbs.

I am running into the same type of problem. I am also getting fuel in the top end of the carburetor which I have never seen before.

These Carbs were gummed up and it looked like it was going to be the typical fix. quick and easy, not these carbs. I have had all the fuel circuits apart and cleaned everything.

I still have a huge stumble off idle that is not acceptable, the bike will stall if you don't baby the throttle or use the choke.
Once the bike is going the Main jet circuit is spot on. It pulls and runs fine.
Also the hotter the bike gets the worse the symptoms are.

I do know that at some point during this maintenance my needle and seats in one or more carburators have not seated because I had enough fuel in the crankcase that I needed to change the engine oil.

I don't want to order a rebuild kit if the float was just stuck but I believe this may be my off idle problem, fuel in the crankcase, and fuel in the upper carb problem all together.

If the float level was consistantly this high due to not shutting the fuel off at idle, would this create these problems including the off idle stumble.

I read a comment about the fuel pressure possible being to high but I think if the float, needle, and seat system is working properly it should stop the fuel and maintain proper levels. I have worked with Race Car fuel systems and automotive as well and if you consider there design they also use a pump, which is probably at a similar pressure or higher, and the system uses the same design to stop the fuel and maintain a fuel level, which is a needle and seat design.

I do think that the pump in this particular system, (a motorcycle), may give us some symptoms during troubleshooting that we are not used to seeing on a motorcycle due to the fact that most carburated bikes don't have a fuel pump.

The more I think about the problem the more I am leaning towards ordering the parts to replace the 4 needles and seats in these carbs.

Any thoughts, comments, or advice, would be appreciated.

Thanks Sven
 

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Maybe all your needle and seats are not in good condition causing the problem in all your cylinders. therfore swapping parts between carbs wont help. Just an idea.
Sven
 

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I had a similar problem a few years ago. One of the 4 carbs flooded like crazy. In the end it turned out to be the petcock. The bike had an auto petcock (like most all our bikes), the fuel turned on automatically when the bike was running. They do this by connecting a vacuum line from one of the carbs to the petcock. When the valve feels some vacuum it lets the fuel go, simple enough. However, my petcock had a bad diaphragm in it. when the bike started instead of opening the petcock with vacuum, it was sucking raw fuel through the vacuum line into the number 2 carb. Rebuilt the petcock and the problem was fixed.
 

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Don't know if this applies to the particular year 9R in question, but bikes with fuel pumps don't have vacuum-operated petcocks. On my ZZR 12, you can leave the petcock "On" all the time and no fuel passes by the pumps. If you disconnect the fuel line to the pumps without turning the knob to "Off" fuel pours straight out. With a vacuum petcock, no fuel flows unless there is engine vacuum. These are for gravity-feed fuel tanks.
 
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