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Thread: 2.25 petrol - poor running with Zenith

  1. #11
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    I may be available in a few weeks time. Keep us posted once you've addressed the "known issues" and we'll see how things stand in two weeks.

    I agree with Discodicky that the Zenith is a better carby than the Solex (aka 'Slowleaks') provided you keep on top of the recurring warping issue.
    Roger


  2. #12
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    Quote Originally Posted by Discodicky View Post
    I was working at local Hobart LR distributor way back in early/middle 1970's and distinctly recall having some faulty Zenith carbs on the 4 cyl engine. There was an LR Service News and we had to replace the carby.
    The problem was running way too rich at idle and wouldn't respond to mixture adjustment.

    In my opinion the Zenith is far better than the Solex.


    Someone on here bought a Chinese Lookalike Zenith & experienced rubbish running. I can't place a name but he will probably read your post. I think it was given the heave ho in the end.


    I experienced a problem with my original Zenith & it turned out to be a high carby float level. Sorted that & 8 years on she still runs like a charm.
    Well as charming as a '66 LR can.

    Warping. That did occur early in it's life but was rectified ok.

  3. #13
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    Just thinking about the movement you experienced with the distributor, you might check that the large clamp around the shoulder at the base of the distributor is correctly located ON the shoulder. This is the course adjustment for your timing. The bolt which secures that clamp to and engine block via the slotted hole in that clamp also serves as a fine adjustment for your timing and the micrometer adjustment on the side of the distributor serves as an 'ultra fine' adjustment for your timing.
    I used to set the static timing to between 6 & 9 deg BTDC then ultra fine tune by road testing and using the micrometer adjustment.
    Roger


  4. #14
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    Quote Originally Posted by Xtreme View Post
    Just thinking about the movement you experienced with the distributor, you might check that the large clamp around the shoulder at the base of the distributor is correctly located ON the shoulder. This is the course adjustment for your timing. The bolt which secures that clamp to and engine block via the slotted hole in that clamp also serves as a fine adjustment for your timing and the micrometer adjustment on the side of the distributor serves as an 'ultra fine' adjustment for your timing.
    I used to set the static timing to between 6 & 9 deg BTDC then ultra fine tune by road testing and using the micrometer adjustment.
    Thanks for the pointers - this is all stuff I'm doing for the first time, so there may well be a thread next weekend with more questions about this! I've got an electronic ignition kit so I might also take the opportunity to install that if I'm fiddling with the distributor.

  5. #15
    JDNSW's Avatar
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    As noted above, there have been issues with Zenith carbies (and copies).

    Most of these relate to the seal between the top part of the carburettor and the main body. There are two issues. First, and most common, is that the top section is not flat on its mating surface. This needs to be flat to properly seal several passages going between the top and bottom. If you take the top off, and remove the emulsion block, float and needle valve, the top can be flattened using a piece of plate glass and fine wet and dry. Take care in reassembling that the screws holding the emulsion block are not burred - there is not much space for their heads, and a burr on them can undo the work you have just done.

    The other potential issue is that this design depends on the O-ring in the throat to stop direct suction of fuel from the bowl. Any damage to the O-ring or the sealing surfaces can result in a leak as can a hardened O-ring. It does not take much, as there is a high vacuum here at idle.

    However, as you found your distributor loose, I suspect this may be a lot of your problems. If you can get it idling and rotate the distributor for the best running, and clamp it at that, it will be pretty close.

    Another potential issue is air leaks anywhere into the induction system - most likely is the gasket below the carburettor, or the vacuum advance line, or the PCV system (if fitted), but manifold to head is also a possibility.
    John

    JDNSW
    1986 110 County 3.9 diesel
    1970 2a 109 2.25 petrol

  6. #16
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    An update on this - I reset the timing as per the manual, and replaced the fuel pump as part of fixing the fuel leak (unrelated to the starting issue). It's no better than before, I still think it needs a second pair of hands to tweak the distributor while I try starting it (or vice versa). If anyone here is still willing to pay a visit, I'd appreciate that. I have this week off work for unrelated reasons, and this weekend would also be fine.

    One other avenue I'd like to explore - the original copper vacuum line was rubbed through, so I replaced it with a more modern flexible vacuum hose. The inner diameter of the hose is irrelevant, right? Since the pressure on the vacuum advance mechanism will be determined by the area of the diaphragm inside the distributor multiplied by the absolute pressure. I'm thinking of using a bulldog clip or clothing peg to clamp off the vacuum tube, just to isolate the effect of rotating the distributor from the high vacuum at zero throttle. Is this a pointless exercise? I realise I'll probably need to tweak it again once I un-clamp the vacuum advance hose.

  7. #17
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    Correct, diameter of vacuum line is irrelevant. I do not think it would be useful to clamp off the line - just pull it off and block the (manifold) end. The distributor end does not need blocking. But if you set the distributor timing with no vacuum, this will be incorrect when you reconnect it if you set it while idling. If setting with no vacuum advance, it needs to be set at full throttle and load - a bit difficult to do except by "take it for a drive and see if it is any better or worse, stop, adjust a degree or two, repeat". If you are doing this, you might as well do it with the vacuum connected, starting from the static setting. Provided the distributor has the right advance curve for both both vacuum and centrifugal advance, it only needs setting at one point. And apart from making sure that the centrifugal advance moves freely and there are no vacuum leaks, there is nothing you can do to change these curves.

    I'll repeat what I have said before - what looks like carburettor problems can be ignition, and vice versa.
    John

    JDNSW
    1986 110 County 3.9 diesel
    1970 2a 109 2.25 petrol

  8. #18
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    Quote Originally Posted by JDNSW View Post
    But if you set the distributor timing with no vacuum, this will be incorrect when you reconnect it if you set it while idling.
    Thanks. Yep, I'm aware of this being an issue - the main thing I'm trying to do is isolate where the behaviour of "applying throttle kills it" is coming from. My idea was that if removing the vacuum advance lets me apply throttle, that indicates timing is too far retarded. Otherwise, I can focus on the carburettor.

    I'm also planning to hook up a dial indicator to the exhaust port on cylinder 1 and see where valve timing is. My understanding is that with the "EP" mark on the flywheel at the pointer, it should be at, or very close to, the bottom of its travel. I've got my fingers crossed that this is right, I'm not looking forward to pulling the sump/water pump/timing cover etc. if it's wrong.

  9. #19
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    Land Rover Treasure Shop | all the parts you need for your Land Rover!

    is where i got my solex carby from

    i found it to be better than any zenith or weber i ever had on the truck
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    1996 Discovery 300TDi Auto
    2012 SZ Territory TX 2.7TDCi

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  10. #20
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    G'day Will,

    My daily driver for 45 years is a 2A 1966 SWB 2.25 Ltr petrol.
    This is what I would do:
    Set the contact points gap to 16thou as per manual. Replace capacitor. Spark plug gaps set to manual specs.
    Set the static timing to 6 deg BTDC. This is your datum point. You don't need to change it until ready to fine tune.
    Check that the vacuum advance is working by sucking on the connecting tube and observe the movement of the contact breaker plate.
    (By all means check the valve timing using your dial gauge on no1 exhaust valve peak. You will find it is retarded hopefully only a few degrees.) Valve timing is critical in tuning these engines. I fitted a Zeus gear drive to my engine.
    You are not tuning your engine, you are just getting it to run properly at this stage.
    The Solex B40PAIO carburetor is what I use. (There is a sticky on the Solex to understand how it works and repair.) All the jets are external and so when your ready to tune it's easy to swap out jets. I make my own air correction jets and have a variable main jet system fitted.
    The problem with the Solex is the die cast material goes soft over time and seats leak and threads break. Go easy with the spanners.
    Four things to look for are main jet carrier leaking, air correction jet fitted with a washer, float needle and seat worn badly and leaking at thread and throttle plate spindle worn and leaking.
    The leaking spindle causes poor idle and a weak mixture on quick acceleration.
    (Carburetor Services at Burwood used to re-bush the spindle bearings with Teflon bushes.)
    I would pull your Solex apart and clean the galleries with Carburetor cleaner and compressed air and re-assemble with new gaskets and accelerator pump diaphram making sure the jets are the correct sizes as per manual. Make sure the mounting flanges are flat.
    Start a repair/maintenance log book.
    Plenty to think about!.

    Chris

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