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Discussion Starter · #1 ·
I have currently bought a 1981 Kawasaki KZ550 ltd and im experiencing a lot of trouble with the fuel system. When the motorcycle cranks the thing sounds like it is starving for fuel. It has a vacuum petcock on it but i have cleaned that and still no luck. There is no suction coming out of the vacuum line therefore it is not pulling the fuel in to the carburetor. What can i do to fix this problem? The bike will crank but when i go to give it throttle it sputters and goes dead. Any help would be greatly appreciated.
 

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itching to ride
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Have you tried starting it on prime? You need to track down why you have no vacuum. The other end connects to one of the carbs so check to see if it is connected and check to see if you have any breaks in the hose.
 

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Hi. If it was a non-runner for any length of time, it may need a good old classic tune up. Start with valve clearances, as the valves need to close near perfectly to create the vacuum and pull fuel at cranking speed. Then make sure you've got a strong timed spark. And afer you are confident that these two issues are well in order, start with the carb fettling. These carbs are super precision instruments and will work beautifully, but they need to be cleaned and service almost like your a watchmaker in the days that such things kept time with low frequency mechanical oscillations.
 

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Need Time To Ride
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Give it a shot of starting fluid. If it starts, tear apart and clean the fuel system. If the bike has been sitting the fuel system is likely full of crud. Piston rings can take a set from sitting and will take a few thermal cycles to properly seal again. The vacuum is not your problem at the moment. If the fuel bowls are full the bike will run for a few minutes even with the full turned off.
 

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Discussion Starter · #5 ·
It was running a week ago but when i went to ride it a couple of days, it still cranked it just idles for a little but then goes dead. It can stay running but i have to switch it back to prime every couple of seconds to keep it running. Im wondering if the carburetor could be clogged up because there is a lot of rust in the gas tank and i havent been able to replace it yet. Could it be the Carbs?
 

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GHOSTRIDER
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It was running a week ago but when i went to ride it a couple of days, it still cranked it just idles for a little but then goes dead. It can stay running but i have to switch it back to prime every couple of seconds to keep it running. Im wondering if the carburetor could be clogged up because there is a lot of rust in the gas tank and i havent been able to replace it yet. Could it be the Carbs?
Does the fuel line have an inline fuel filter? If not, GET ONE! Heres the deal. Your carbs are probably clogged and are going to need cleaning. Cleaning the carbs will do no good if the tank isnt cleaned and a new fuel filter isnt installed first. Particles of rust will filter through the petcock screen and build up inside the petcocks seals and cause the petcock itself to malfunction. some of that sediment debris goes right down into the carbs and clogs the tiny passages causing the carbs to malfunction, so a thorough carb and fuel system cleaning is in order,including the petcock! PS, No amount of fuel additive(seafoam,b12,etc.)will dissolve rust.
 

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Discussion Starter · #7 ·
ok thanks im going to clean the carbs tomorrow. yes it has a fuel filter on it. Hopefully i will have a new tank by next week. So if the carbs are clogged would that cause the vacuum to stop working?
 

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"It has a vacuum petcock on it but i have cleaned that and still no luck. There is no suction coming out of the vacuum line therefore it is not pulling the fuel in to the carburetor."

It NEVER pulls fuel into the carburetor..The intake vacuum simply opens the petcock and allows fuel to flow into the hopelessly plugged up carburetors through the fuel lines. If there is fuel in that vacuum line, then the diaphragm in the petcock has ruptured and needs to be replaced or discarded and replaced with a manual petcock.. If the tank is full of rust, the entire fuel delivery system will have to dissembled and cleaned out..There are no short-cuts..
 

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Discussion Starter · #9 ·
Theres no fuel in the vacuum line and the diaphragm is fine. Im getting rid of the old tank and getting a better one. Im am going to clean out the whole fuel system and see what happens. thank you for the help
 

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GHOSTRIDER
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ok thanks im going to clean the carbs tomorrow. yes it has a fuel filter on it. Hopefully i will have a new tank by next week. So if the carbs are clogged would that cause the vacuum to stop working?
If the carbs are clogged, the engine cannot run, there is no vacuum when the engine is not running. The inside of a vacuum operated petcock has a spring that "closes" the flow of fuel when the engine is not running. The fuel should flow at all times when the petcock is the "PRI" position and will only flow in the "ON" when the engine is running. It sounds like you may have a "vent" line confused with the vacuum line if you dont have vacuum while the engine is running.
 

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Here is another twist that beat me for a few hours a while ago. Usually the fuel tap prime position draws from the lower reserve standpipe inside the tank. This lower stand pipe means a high liquid head of pressure, which might just provide enough fuel for sustained running. But still, clean and restore the system so you can make it back home without bothering your friends with trailers and vans.
 
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