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  1. #1

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    Fuel Pressure Insufficient on 1997 GTX to start or run

    Is the only 'fuel pump' on this machine the small rubber 'baffle' type pumps in the carbs?

    What is the purpose of the 'pulse line'?

    I have changed out all fuel and vent lines on this machine, and cleaned the selector valve and the small screen filter on the bottom of the fuel pickup in the tank. The machine was running like a champ beforehand, but regularly had fuel 'gunk' in the screw off filter under the hood. It had the original grey fuel lines so I was trying to head off a problem before it showed up.

    Now with new, clean fuel lines and squeaky clean carburetors, and with fresh fuel, the fuel filter under the hood fills with fuel, but I am not getting fuel flow through the (new & clear) fuel line going to the carbs.

    I found this because I cannot get the machine to run, though it does turn over and over, and my inductive timing light shows a signal going through the spark plug wires.

    No fuses are blown, and I originally thought I had fuel delivery and no spark, but I now believe what I thought was fuel being delivered to the cylinders and showing up as 'wetness' on the spark plugs, was oil and not fuel.

    Any suggestions on how to track this down and find out if I am getting sufficient fuel pressure/delivery?

    Does anyone know what the fuel pressure should be on this machine?

    Thank you!

    (Had previously posted this as a 'no spark' problem and I appreciated the help given there, but as nothing suggested solved the problem I continued research and testing and now believe I am dealing with a fuel problem. I have not been successful in finding a proper procedure for the re-installation of these carbs after rebuild, and if there are fuel-line bleeding or line-filling procedures that must be followed.)


  2. #2
    Tiny's Avatar
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    The purpsose of the pulse line is to operate the fuel pump..It takes the pressure and makes the diaphram move.....

  3. #3
    To answer your question, yes, the only pump is the one in the carb. First question, are you sure you have all the fuel lines in the right places?

    It is often hard to get the whole fuel system primed at the beginning. I have used a couple methods. One is to apply a low pressure, like 5 psi, to the fuel tank, which then forces fuel through the system. The other way is to unscrew the plugs, squirt some fuel in the holes, then replace plugs, start up, repeat a few times.

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  5. #4
    Tiny's Avatar
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    The easiest way is to pull the choke and pin the throttle wide open....It will start within 10 seconds...You may want to do this twice..Dont want to overheat the starter...Do it for a few seconds stop, wait 10 seconds and do it again..

  6. #5
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    I go with the premix down the jugs to spin the engine up..a few shots is all that should be needed to prime up the system, assuming everything is in order.

    NO STARTER FLUID

    if the water trap ( filter under the hood) is filling, you are certainly pumping fuel.

    did you have the carbs apart?..there is an important fuel filter in each carb that needs to be cleaned/changed..one might be so plugged you can get the fuel into the carbs..certainly seems to be able to suck the fuel into the water trap....

  7. #6

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    Quote Originally Posted by Tiny View Post
    The purpsose of the pulse line is to operate the fuel pump..It takes the pressure and makes the diaphram move.....
    Is the pulse line using vacuum to move the diaphragm, or pressure?

  8. #7

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    Thank you for the answer about the only 'pump' being in the carbs. I suspected so because I could not determine where else there would have been a pump. I thought before removing the fuel pickup assembly from the tank that it might have an in-tank electric pump similar to modern fuel injected automobiles, but obviously it does not.

    I understand about your method of pressurizing the fuel tank, but after a few times of trying to crank the engine, the screw-on fuel filter under the hood is full of fuel, so I assumed fuel is being drawn out of the tank as it is supposed to be.

    I'll try the fuel in the cylinders process today.

    Thanks~

  9. #8
    This is how I run a jetski shop in the desert nmpeter's Avatar
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    Quote Originally Posted by Greyhair View Post
    Quote Originally Posted by Tiny View Post
    The purpsose of the pulse line is to operate the fuel pump..It takes the pressure and makes the diaphram move.....
    Is the pulse line using vacuum to move the diaphragm, or pressure?
    <both>

    the pulse line is connected to the crankcase and operates the pump with an "in-out" motion controlled by crankcase pressure ( which alternates between vac and pressure)

    pretty much the same as an old mechanical style car fuel pump, with the exception that the pump diaphragm is moved mechanically and not by air pressure

  10. #9

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    I'll try the premix and see if I can get it to start that way.

    Assuming no starter fluid because it is too rich? And has no oil mixed-in?

    Yes, the water trap is filling. Thanks for confirming that means I am pumping fuel.

    Took the carbs completely apart and cleaned everything. Soaked the carbs in a carb soak for 2 hours. Blew everything out with air pressure. Cleaned the small filters with a method found here using pill bottles and carb cleaner, then dried them with compressed air. Very clean upon reassembly.

    I have been an auto mechanic (shade-tree) for years so I know how important it is to keep things clean, re-assemble properly, check vacuum and pressure items, etc. The only thing I am not completely, entirely certain of is that I have the lines back in place properly as I had a 'helper' on that part of it.

    The main thing that doesn't seem right to me about this is that with the fuel line coming from the water filter to the carbs disconnected from the carbs, when I crank the engine...no fuel is coming out of the line, but if the fuel is drawn by vacuum being created inside the carbs, and not 'pushed' by a fuel pump of some kind to the carbs, then this would be normal as there is not actually fuel 'pressure' , but fuel line 'vacuum', right?

  11. #10

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    Ah...that makes sense. Thanks for explaining.

    So since there is only one pulse line, and it connects to only one of the carbs on this machine...and since the fuel line coming from the water trap to the carbs only connects to one of the carbs, then fuel is fed to both carbs from this one line, and essentially from only one pulse line?

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