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Funny idle when hot... need advice

Discussion in '40- & 55-Series Tech' started by REZARF, Jul 1, 2005.

  1. REZARF

    REZARF

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    Howdy-

    Past few days I have had a problem getting a smooth idle right after restarting the 2f if it is already hot.

    I used the choke to smooth it out and after I ran it a block or so, everything smoothed right back out (and the choke was not engaged anymore either). It will run smooth until I park it again, and it only idles rough for the first block or so. When rough I am erratic around 550 rpm, when smooth I am just over 800 rpm.

    Only thing that is different is I moved to higher elevation in Colorado, about 5K ft or so. My carb may need adjustment, but it ran great back in Iowa before my move (Jim C. carb)

    Any ideas... I was thinking a stuck PCV valve? What should I check?

    Thanks in advance

    REZARF <><
     
  2. FJ40Jim

    FJ40Jim The Cruiser Whisperer SILVER Star

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    Sounds like it's boiling fuel. This is made worse by high ambient temps (it's summer) and by lower atmospheric pressure (like at higher elevations).

    The snorkel is helping by ramming cool air through the carb, ameliorating the cooked carb symptoms. Check to make sure there is no functional hot air door in the bottom of the air cleaner inlet anymore. Also, check the heat riser for proper operation.
     
  3. REZARF

    REZARF

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    Thanks Jim-

    Still the best bucks spent on my cruiser was your rebuild, Thanks!

    I will check the little trap door on the air cleaner, sometimes it does move after a while. I didnt think to check there.

    Heat riser? I have headers, does that mean I have lost my heat riser. Not too sure about that.

    It has been running a bit warm as I run up the hills out here, I also need a shroud I swapped to an fj60 motor with the clutch fan and I lost the orignal shroud due to fitment.

    thanks in advance-

    Rezarf <><
     
  4. FJ40Jim

    FJ40Jim The Cruiser Whisperer SILVER Star

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    Yes, if headers are installed, then heat riser is gone. The odd thing here is that usually instaling headers cools down the intake manifold enough that carb boil-off is no longer an issue. But it certainly sounds like there is still a heat soak problem.

    You do need to disable the hot air door in the air cleaner. It is currently in the cold start position (sucking hot air off the header) and will stay there until the engine bay temp gets up to something silly, like 160deg F.
     
  5. REZARF

    REZARF

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    Sweet, I will take care of the door.

    Jim, at what elevation do I need to rejet my carb? I am living between 5-6K feet, and will be veturing into the high country for trail rides... 10-13K

    I assume a rejet is in order?

    Rezarf <><
     
  6. FJ40Jim

    FJ40Jim The Cruiser Whisperer SILVER Star

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    Yes, at 5k' MSL, the sea level mixture is going to be pretty rich. Sharper response and slightly better fuel economy should be realized by leaning the jets to the altitude appropriate numbers. Also, due to the lower cylinder pressures, ignition timing can be advance a few degrees.