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  1. #1
    Join Date
    Oct 2009
    Location
    Tavistock, Devon
    Age
    71
    Posts
    1,351

    Not Cobra but Jag

    Hi chaps,
    with all the knowledge on here I thought I would ask for some help with my Jag.
    1968 Mk2 fitted 1964 S type 3.8 engine.
    Running ordinary ignition with 2 HD6 carbs and the ubiquitous auxiliary carburettor choke that comes with them.
    New dizzy innards, condenser, points rotor arm (red) leads and dizzy cap. Coil is fairly new and is the sports type.
    Obviously I haven't been able to take it out so it has been sitting for some time.
    Took it out for a run to get some fuel and it conked out. Not missfuelled.
    The RAC chap took a long time in trying to find the problem, sometimes it would start but not run for more than a few minutes and trying a bit of throttle stalled it.
    I then put on my spark plug tester on one of the plugs, just to see and tried running again with the result that you could see the spark get weaker and then it conked out again. Towed home.
    At that time it was fitted with a electronic module which I have now taken off and reverted back to old school contact breakers.
    Put on the old set of points and off it went lovely on a different coil. Took it for a run, going lovely, then it conked out again, no restart.
    Mrs came to tow me home.
    I have tried different coils, all of which tested OK. Everything in the circuit is new. There is fuel pressure and the pump is good.
    Again this morning after receiving the new condenser, points and rotor arm she fired straight up instantly, the choke cut out as it is supposed to and it ticked over lovely, timed it and let it run for a while before switching off. Cracked it I thought!
    Sorted out the scaffolders who had arrived, went to start it again and it took a while before going, then after a while conked out again, no restart. This is doing my head in!
    Let it cool down for 1/2 hour then restarted, no probs, sat and watched the spark plug tester. After aboout 10 mins it started to miss, could hear and see it, got worse, then it conked out again!
    I have checked most things but in case there is something that I have missed then please chip in, I have probably missed something glaringly obvious!
    TIA
    Cheers,
    Murray


    That's the trouble with you Sailors, long hair, quick zips and, Oohh, look at the size of that!!

    If I agreed with you, we'd both be wrong.

  2. #2
    Join Date
    Jun 2004
    Location
    Northampton
    Posts
    1,944
    Sounds like you’ve eliminated electrics so fuel might be the culprit. I have heard of crap in the fuel tank randomly blocking the outlet. Bugger to diagnose but because of the age might be a possibility. Don’t know if an endoscope would help?
    Dek

  3. #3
    Join Date
    May 2004
    Location
    Cowbridge, United Kingdom
    Age
    63
    Posts
    10,258
    Dodgy ignition switch maybe?
    maybe cranking but coil power?
    My Mustang had a very similar issue, that turned out to be a faulty ignition switch.
    Kev Davies
    South Wales Area Rep. UKCC Membership Secretary
    DAX Mk4, 383 Chevy Stroker, Tremec. SOLD
    Contemporary CCX 3-4028, 445ci Big Block FORD FE,TKO 600, Old School IVA'd and SOLD
    Dax De Dion LS2 and T56 IVA'd June '17 SOLD
    1965 Ford Mustang 289 Convertible SOLD
    In build- Hawk 289 Sebring Awaiting IVA

  4. #4
    Join Date
    Aug 2007
    Location
    Bournemouth
    Posts
    539
    I would check or change your fuel filter. If the filter is starting to block then the car will miss during hard acceleration. If it’s clogged symptoms would be what you have now. After a while fuel will ‘filter’ through and the car will start.
    Have you replaced any fuel hoses lately? If so was the hose the correct grade? Wrongly graded hose will degrade and start to clog the passages.
    Also take a look at the carb mounts? I think they are mounted on rubber shock mounts which can split with age and cause big air leaks.

    Check the ignition leads and HT lead from the coil to the distributer. Check for chafing against other metal which could cause arcing. Any escaped sparks from a bad lead won’t reach the plugs. Older leads also become porous which is not a good thing. Damp porous leads are very good conductors and will cause your high voltages to not reach their destination, but rather escape to neighbouring metal.
    David.

    Life is driving the Cobra. The rest of the time is just waiting................till I fix it!

    Wessex region caretaker rep.

  5. #5
    Join Date
    Oct 2009
    Location
    Tavistock, Devon
    Age
    71
    Posts
    1,351
    A video of the stall https://youtu.be/n2pT5f-K7Sg
    Fuel filters are all new, changed at time of breakdown.
    Hoses are all good, been checked.
    Carbs are mounted on those blocks (can't remember what they are called) they are fine.
    All ignition and coil leads are new and in silicone.
    The ignition switch is new, doesn't get hot.
    Coil is fairly cool too.
    She will not start again until some time later, after it (or something) has cooled down.
    Cheers,
    Murray


    That's the trouble with you Sailors, long hair, quick zips and, Oohh, look at the size of that!!

    If I agreed with you, we'd both be wrong.

  6. #6
    Join Date
    Aug 2004
    Location
    Christchurch, NZ
    Age
    60
    Posts
    2,495
    Fuel tank breather blocked?
    Cheers

    Myles D-W

  7. #7
    Join Date
    May 2004
    Location
    Cowbridge, United Kingdom
    Age
    63
    Posts
    10,258
    Watching your video it suggests that the spark fades away before the stall?
    I think ignition system including the switch would be my first port of call.
    Can you do a temporary bypass, that's what I did on the Mustang and traced it.
    Kev Davies
    South Wales Area Rep. UKCC Membership Secretary
    DAX Mk4, 383 Chevy Stroker, Tremec. SOLD
    Contemporary CCX 3-4028, 445ci Big Block FORD FE,TKO 600, Old School IVA'd and SOLD
    Dax De Dion LS2 and T56 IVA'd June '17 SOLD
    1965 Ford Mustang 289 Convertible SOLD
    In build- Hawk 289 Sebring Awaiting IVA

  8. #8
    Join Date
    May 2016
    Location
    Hockley ,Essex
    Age
    58
    Posts
    368
    If the spark is fading I would still be looking at the ignition circuit for sure,
    have you checked the ballast circuit/resister as you are using a conventional
    ignition system ?
    Resister could be braking down.
    Chris.

  9. #9
    Join Date
    May 2004
    Location
    Cowbridge, United Kingdom
    Age
    63
    Posts
    10,258
    Good shout by Chris there.
    The temporary bypass would also take out the ballast resistor if you have one?
    Sometimes it's a resistive wire rather than an actual resistor.
    Kev Davies
    South Wales Area Rep. UKCC Membership Secretary
    DAX Mk4, 383 Chevy Stroker, Tremec. SOLD
    Contemporary CCX 3-4028, 445ci Big Block FORD FE,TKO 600, Old School IVA'd and SOLD
    Dax De Dion LS2 and T56 IVA'd June '17 SOLD
    1965 Ford Mustang 289 Convertible SOLD
    In build- Hawk 289 Sebring Awaiting IVA

  10. #10
    Join Date
    May 2004
    Location
    Finchampstead, Berkshire, UK.
    Age
    55
    Posts
    3,809
    Quote Originally Posted by mylesdw View Post
    Fuel tank breather blocked?
    That's where my head went! Remove fuel cap and give it another go, easy to eliminate

    Jim

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