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Thread: Carby vacuum lines TB42

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    Carby vacuum lines TB42

    Hey guys. I have a GQ shorty TB42 and it idles a bit rough, cruising at higher revs and it runs perfect, foot down and it splutters a bit and at high revs it splutters a bit (4 - 5 K revs).

    My mechanic checked timing, all good, set at 10, plugs replaced, full service, fuel filter replaced, new K&N air filter fitted, carbon cleaner put through once, running premium fuel. Mechanic said only thing left that it could be was the carby.

    Found a bloke where I am in Townsville who will full recon carby ($450) and block off enviro restrictions n stuff but I thought i would check to see if the vacuum lines are all in the right locations first.

    There appears to be a rogue pipe or vacuum tube coming out from photo (1932), not sure where that one is supposed to go??

    See attached photos.

    Any comments or help would be appreciated.
    Attached Images Attached Images
    Last edited by Alexander Supertramp; 30th January 2018 at 07:04 PM.

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    Not sure from pictures which vacuum line you're referring to(point an arrow to it so we know), but if there is an open one, the mechanic should have noticed it and blocked/plugged/connect it where it suppose to go to.
    If there's a vacuum hose with an open vent ending, then plug it and see how it goes.

    $450 for that Nikki carby rebuild(assuming it is the stock Nikki carby 'cos it sure look likes the one) is way too expensive. Both TB42 & RB30 came with the same carby with very very minor differences).
    You can buy a brand new one from ebay & then pay a good carby tuner mechanic another $100 to tune it properly to suit your engine condition. If rebuilding it, it shouldn't be anymore than $200-$250 & the mechanic who rebuild it should tune it to suit your engine as well, 'cos depending on the engine wear and other conditions slight tuning to suit the specific engine may be/will be necessary.

    Other than open vacuum ports, look for cracked ones that are hard to locate. Spray some WD40 etc into the vacuum lines areas and see if the engine runs differently and whether you hear any hissing. That's how you locate hidden vacuum leaks.

    Sometime, all you need is to pull the carby out and there are three big bolts fitting the throttle body to the main body under the carby. You just need to tighten them and put it back preferably with a new gasket. That bottom gasket can be easily cut using a piece of cardboard. No rocket science at all.

    Getting back to your particular symptoms above, I would open it up and have a good look at the accelerator pump, but that if you're familiar with opening up and fixing carbies. And the only way to get familiar with it is to open it up.

    I've done craploads of threads about that with details & pictures. Use the search function.
    Last edited by dom14; 1st February 2018 at 02:43 AM.
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    RB30, some 2-3 inch lift auxiliary LPG tanks
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    Check the vacuum advance line that goes to the dizzy.
    Ruptured diaphragm or cracked hose can also produce symptoms along above lines in the OP.
    You test the diaphragm for any ruptures by sucking on it to see if you feel a resistance vacuum, but that's a rough test.

    Proper test is described below, but need to take some care not to overload the vacuum with the suction pump so to make sure it
    won't rupture the diaphragm, simply by trying to test it.

    https://www.thoughtco.com/testing-va...ic-cars-726193

    "Testing the Vacuum Advance
    There are a couple of ways to test the vacuum advance on vehicles equipped with distributors. Mechanics like to use an inductive pickup timing light and verify the base timing is set to the correct position first. Then they can connect a hand-operated vacuum pump to the diaphragm, give it a few pumps and watch the timing mark on the crankshaft harmonic balancer advance on the timing scale with the timing light. Nevertheless, those without ignition timing lights can still test the vacuum advance.

    With the engine off you can remove the distributor cap and use a vacuum hand pump to operate the advance mechanism. The diaphragm moves a rod that in turn moves a sliding plate at the base of the distributor and you can see this movement with the naked eye. A few pumps of a manually operated vacuum tester should not only provide full advance, but it should stay in that position until you remove the vacuum from the port."




    BTW, if yours has upgraded electronic/hole effect ignition breaker system inside the dizzy, they you probably wanna test the vacuum advance diaphragm while running the engine(I think) and you mat need a timing light to observe the timing change while applying the vacuum.


    AFAIK, traditional ignition point breaker systems are more sensitive to vacuum advance malfunctioning issues, but don't quote me on that though, I'm only speculating from some experience.
    Last edited by dom14; 1st February 2018 at 03:03 AM.
    RB30, some 2-3 inch lift auxiliary LPG tanks
    Few more mods on the way
    http://www.worldwildlife.org/species/tiger
    https://www.panthera.org/
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    Thanks Dom.

    Too advanced for my mechanical skills. I have found a mechanic who has worked on carbies a lot before so I am taking to him to check it all out before shelling out the $450 for carby rebuild.

    I am hoping that a few new hoses etc will fix it haha. It does have a petronix ignition system already so not sure if dizzy vacuum issue still applies?

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    I read through the GQ service manual and there is 40 pages on Carby adjustments. HOLY SH*T. I will leave it to the other mechanic.

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    Quote Originally Posted by Alexander Supertramp View Post
    I read through the GQ service manual and there is 40 pages on Carby adjustments. HOLY SH*T. I will leave it to the other mechanic.
    Hey mate I know it's an old thread but who was the mechanic in Townsville and how'd it go? I'm in Townsville and chasing someone who's worked on carby patrols

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