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Thread: 4.2 duel fuel petrol not idling

  1. #11
    Legendary dom14's Avatar
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    Quote Originally Posted by Sandman82 View Post
    Hi all, ive tried to find a similar thread, can anyone direct me or have you seen this problem.
    I have a problen on a carby 4.2, dual fuel. The car ran fine on both fuels and regularly was swapped between each. A collapsed muffler was causing it to struggle which i eventually replaced after multiple patch ups. Had trouble with idle on petrol after that however plenty of power. On gas it ran fine. Also lagged on take off petrol only.
    I rebuilt the carby so the power piston stopped lagging.
    Ran perfect on fuel, swapped to gas also perfect. Swapped back to petrol and it wont idle. Still power under load but now backfiring out the exhaust when decellerating and dies under 1000rpm.
    Tested the gas valve by shutting off the tank so its not duel fuelling. Fuel pump is fine and new filter. No air leaks.
    Had another issue at the same time which was the gas solenoid had cracked and was shorting and blowing a fuse (i think) which is why i checked fir duel fuelling from a leaky solenoid.
    What i font understand is why it ran oerfectly for days then after running gas and back to petrol it faults.
    Any idea?
    If I understood you correctly, it's running fine on LPG now, but on petrol it backfires when decelerating and won't idle on petrol either.

    How did you rebuild the carby? Professionally or did you do it yourself?

    I didn't understand what you meant by "power piston stopped lagging".

    Sounds like a carby issue, but it's a very good thing to rule out all possible electrical issues first, including spark, spark plugs, leads, etc.
    As mudnut suggested, it may be a good idea to check to see whether the secondary throttle valve is sticking. Put on a pair of protective glasses before checking the running engine from the top of the carby as a backfire can cook your eyes.
    Backfiring usually means a lean mixture.
    And the main causes of lean mixture usually are, either low fuel pressure(clogged filter, faulty fuel return valve, weak fuel pump, bad contacts to petrol solenoid or fuel tank/pump, carby issues like sticking valves, plunger, etc) or vacuum/air leaks.
    Last edited by dom14; 29th May 2016 at 11:47 PM.
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  3. #12
    Advanced Arfa Brayne's Avatar
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    Symptoms you've described sound like overly lean mixture on the idle/deceleration circuit.
    This would most likely be an air leak into the inlet manifold (which you have ruled out) or a blockage in the idle mixture port of the venturi - possibly stirred up when you worked on the carby.
    However it could also be a very rich mixture at idle cause by the engine cut solenoid on the side of the carby. A lot of people think this is a fuel cut solenoid, but on early Patrols it kills the engine by flooding the inlet with fuel to stop "running on" detonation firing when the ignition is turned off.
    When the power is applied, the solenoid should "click" and you should feel it also with your finger. If there is no click, check for power supply and continuity with a multimeter
    "Can't" is a dirty 4 letter word.
    Best way to deal with a "Can't" is to chop off the "t" and brew it in boiled water for a few minutes.
    Sip on the "t", and consider what you've got left to work with

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