Aisan Carb Expert Needed - 1980 FJ40

Discussion in '40- & 55-Series Tech' started by Jeffrey Davis, Feb 9, 2009.

  1. Jeffrey Davis

    Jeffrey Davis

    Messages:
    12
    Likes Received:
    0
    Joined:
    Oct 3, 2008
    I recently rebuilt my carburetor on my 1980 FJ40 and now it surges or stumbles (lean condition?) between 2000 to 2500 rpms with no load on the motor. It runs perfect at all other rpms. The power valve and associated jet were replaced because the bottom half broke off in the carb during diassembly. I drilled it out without damaging the threads. The power valve jet for this application is a 0.90 mm, but this part has been discontinued by Toyota so I installed a 1.0 mm jet. In addition, the restrictor for the idle jet was missing so I replaced it with an after market 0.50mm jet that came in the kit. The idle jet that came out of my carb was a 0.60 mm. I have checked all of the basics as follows: 1. the fuel level is consistently in the middle of the window, 2. the fuel cut-off solenoid is working, 3. the vacuum advance is working, 4. there are no vacuum leaks, 5. my timing is set at 7.5 degrees BTDC, and there's no junk in the fuel (tank cleaned and coated). Any thoughts or suggestions as what is causing this problem would be appreciated. Could it be caused by the smaller idle jet? I don't think the larger power valve would cause this condition.
     
  2. PhilC64

    PhilC64

    Messages:
    2,575
    Media:
    4
    Albums:
    3
    Likes Received:
    6
    Joined:
    Apr 1, 2007
    Location:
    Peoples Socialist Republic of Chicago
    Tons of folks have done this with decent results. When you search you get these responses. IH8MUD Forums - Search Results

    Secondly you want to start chatting with FJ40Jim aka Jim C. The man is a guru with carbs.
     
  3. Pin_Head

    Pin_Head

    Messages:
    14,761
    Likes Received:
    2,432
    Joined:
    Feb 6, 2002
    Location:
    OC, CA
    Surging and stumbling sound like two different things to me. Which is it? Is the secondary opening?
     
  4. Jeffrey Davis

    Jeffrey Davis

    Messages:
    12
    Likes Received:
    0
    Joined:
    Oct 3, 2008
    I would describe it as surging (rpm's up and down). I looked down the primary at the nozzle and the fuel stream cuts off and on at around 2000 rpms. The secondary is fully closed.
     
  5. FJ40Jim

    FJ40Jim The Cruiser Whisperer SILVER Star

    Messages:
    10,352
    Media:
    1
    Likes Received:
    2,731
    Joined:
    Sep 26, 2003
    Location:
    Lancaster, Ohio, USA
    Verify that the coasting decel fuel cut system is working properly.
    backprobe the ground side of the ICS connector, w/ voltmeter connected to good ground. It should always show zero volts. If the meter is showing voltage while the surge is happening, then the decel fuel cut system is the culprit.

    Not likely. A small idle jet would cause the A/F to go lean in the 1000-1500 range.

    Right, the PV is out of the picture at low load.

    The symptom could also be caused by having the boosters reversed.
     
  6. Jeffrey Davis

    Jeffrey Davis

    Messages:
    12
    Likes Received:
    0
    Joined:
    Oct 3, 2008
    The coasting decel fuel cut-off system was the culprit. The ground side of the ICS connector showed current during the surge condition. I connected the solenoid ground wire to one of the air horn screws and the other wire to a source of switched voltage, problem solved. The PO (father in-law) removed the vacuum switch for the decel system 20-years ago as part of the de-smog. Now I understand the reason for the "green wire mod", but would prefer to get the decel system working again. Thanks Jim. I would have never figured this out without your help.
     
  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.