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  1. #1
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    Optimax High Fuel Pressure - Check Valve?

    Good Morning,

    My 2002 135HP is running higher than normal fuel pressure. When running, I am getting around 110 / 115psi on the fuel side. The motor is coughing at idle, and you can smell how rich it is running. Suspecting a sticking 40psi check valve on the VST return, I removed it and plugged in a primer ball valve for a quick test, because of its internal check valve. My running fuel pressure dropped to 87/88 psi, which is 10 psi higher than my air side. Rich fuel smell went away, and the idle started to stabilize, but I am sure the plugs are now toast and will need to be replaced. After that test, I ordered a new 40psi Mercury check valve, and installed it last evening. When I fired the motor up, my fuel pressure stabilized at 100 / 105psi, while air pressure was at 77/78 psi. The idle coughing returned, and it started to smell like it was running rich again. Looking at the package the check valve came in, it looks like the “new” part was a new old stock from 2003.

    Is there anything else that could be causing this high pressure, or is everything pointing at both the old and the “new/old” check valve being bad? The only other things I can think of would be a deformed fuel regulator spring or a clogged return line, but I would think both of those would keep the fuel pressure high when I put the primer ball valve in? I also need to mention that once the motor is shut off, fuel pressure drops to 20psi and holds there. From that, I don’t think I have any leaks in the fuel regulator / tracker diaphragm but I have not inspected them.

    Final question – I know my air pressure is lower than it should be. I have tested the air side with regulated shop air and do not have any leaks. However, the regulator is blowing at 77/78 psi. My regulator is the old style, single unit type instead of the spring and diaphragm type. Is this type of regulator adjustable or is it just a replacement part?

    Thanks for your help.

    JW

  2. #2
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    Well, pressure is controlled by the fuel reg dia so I would def pull and inspect it. Do it carefully, strong spring in it....I used some longer screws with nuts in place of two of the existing screws and backed off on the nuts till it was loose. Replace same way. Spring may be corroded..

  3. #3
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    The spring is certainly something I was suspicious of. Just curious, does anyone know if that spring is actually available from Mercury? I can't find any parts diagrams of the fuel regulator. I know the diaphragm is now available, so I would assume other parts would be available too?

  4. #4
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    spring is 804534 part number Diaphram is 804533

  5. #5
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    vnemous,



    It looks like that spring and diaphragm is for the tracker valve. Is the spring the same?

  6. #6
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    Yes thats the tracker, I should have read more carefully, sorry.

  7. #7
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    Fuel Regulator Service Kit 8M6002989

    spring in kit not sold separately.

    Service Bullitin is SOB 15-18

  8. #8
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