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  1. #1
    Join Date
    Feb 2014
    Location
    Congleton Cheshire
    Age
    64
    Posts
    25

    Help guys I keep blowing fuses

    Hi All

    I am 95% finished with my Dax build.

    It has a stroked SBC, Holley carb and Mallory dizzie with electronic ignition. and all check out fine - spark at plugs etc.

    It seems to be wired right (I did it and I've built cars and wired them before), but now I've got a weird issue that's just begun. It has turned over fine on the key for a few weeks now, and all electrics work fine, but last week, when I'd finished all the carb installation, I was trying for first start and it has started blowing fuses.

    When I try to start, it turns over well and all seems normal, but then when I release the key back to Position II, it blows the main fuse.

    It now does it all the darned time - problem is - I haven't done anything to the wiring to cause this change - it just blows the fuse on stand down.

    Any thoughts/suggestions would be very much appreciated.

    Cheers

    Confused Gary

  2. #2
    Join Date
    Jul 2013
    Location
    Hertfordshire
    Posts
    532
    Could it be a faulty key barrel? Causing a short?

  3. #3
    Join Date
    Jan 2006
    Location
    Chelmsford Essex
    Posts
    1,739
    I would remove your wiring off position 2 fuse and only have the attach the solenoid wire . This is all you need to activate the the starter motor. Then attach each circuit one at a time to locate which wire feed is causing the issue. What fuse size is blowing?
    John Desz

    Essex & Herts Area Rep. UKCC

    Dax 351 Cleveland T5 2.88 PL

    Events posted and meeting updates follow Face Book.

    https://www.facebook.com/groups/170236225077355

  4. #4
    Join Date
    Feb 2014
    Location
    Congleton Cheshire
    Age
    64
    Posts
    25
    Hi Jon thanks for the response - I'm going to do exactly what you suggest - its blowing 10 Amps, so no trickle by any means.

    I just can't work out why it doesn't blow on max drain when I'm trying to start the thing, but on power down when I switch the key back - obviously, the Pos II circuit is made when I turn the key on in the first place and yet it doesn't blow then.

    I will isolate Pos II and try it.

    Watch this space!

    cheers
    Gary

  5. #5
    Join Date
    Feb 2011
    Location
    Northampton
    Age
    43
    Posts
    4,944
    You don't have a ballast resistor that is bypassed during start but back in circuit in pos2, do you?

  6. #6
    Join Date
    Mar 2006
    Location
    Oxfordshire
    Age
    69
    Posts
    1,742
    Hi Gary.

    Does your Holley carb have an electric choke? If so, as this started after you'd installed the carb, I'll bet that's the problem!

    Try disconnecting the 12v feed to the electric choke.

    I don't like the way the electric choke works - it's drawing pretty high current all the time to keep the coil heated that in turn keeps the choke off. So I'd recommend installing a Holley manual choke conversion kit.
    Alan

    Ex CRC Thames Valley Regional Rep - please contact me if you're interested in taking on the role!
    UK Rep for European Cobra Club (eurocobra.boards.net)

    Dax 427 DeDion - now sold
    2003 E85 Z4 3.0i - the new toy!

  7. #7
    Join Date
    Feb 2007
    Location
    West Sussex
    Posts
    9,622
    Quote Originally Posted by conrod View Post
    Hi Gary.

    Does your Holley carb have an electric choke? If so, as this started after you'd installed the carb, I'll bet that's the problem!

    Try disconnecting the 12v feed to the electric choke.

    I don't like the way the electric choke works - it's drawing pretty high current all the time to keep the coil heated that in turn keeps the choke off. So I'd recommend installing a Holley manual choke conversion kit.
    that's interesting- how much current do you think its taking? I have one in operation at the moment.
    Crendon Chassis No.49
    Huddart FE428 + toploader

    Not listed in the Shelby Register.

  8. #8
    Join Date
    Mar 2006
    Location
    Oxfordshire
    Age
    69
    Posts
    1,742
    I hooked a spare electric choke up to my bench power supply. When first connected at 12v the current exceeds that on my power supply ammeter, so is greater than the maxumim reading of 2 amps. As the coil heats up, the resistance increases, and the current therefore steadily falls to about 0.75 amps. It's a bit strange, as the resistance reading when cold on my multimeter is 10 ohms, so the initial current at 12v should be 12/10 = 1.2 amps rather than in excess of 2. From the speed at which the ammeter moves and the noise as it hits the end stop, I'd say it's around 3/4 amps - any greater and the PSU's breaker would trip.

    Holley recommend a 10 amp fuse, and I've just found this thread, which contains the following post:

    "Out of curiosity, I just tested the current draw on an electric choke I had sitting around. For the first 1/4 second, it spiked at 6.5 amps and dropped to 1.3 amps. After that, as the coil heats up, it steadily dropped from 1.3 and leveled out at about .75 amps. So that explains the need for a 10A fuse when the device only draws an average of less than an amp."

    Gary says it's a 10 amp fuse that's blowing, so either it's something else on the ignition controlled 12v circuit, or the choke (or the wiring to it) is shorting to earth.

    I always felt uncomfortable with a constant live extremely hot primitive electrical device being attached to the carburettor!
    Alan

    Ex CRC Thames Valley Regional Rep - please contact me if you're interested in taking on the role!
    UK Rep for European Cobra Club (eurocobra.boards.net)

    Dax 427 DeDion - now sold
    2003 E85 Z4 3.0i - the new toy!

  9. #9
    Join Date
    Feb 2007
    Location
    West Sussex
    Posts
    9,622
    Thanks Alan, I think my fusing may be under-rated I'll take a look.
    But you are right - a manual choke would be better.
    I know others who have simply removed the choke flap altogether, but I was a bit anxious about doing this.

    I have also had similar issues as the OP with the pusher fans on the front of my car blowing fuses, so again, I think that's an initial issue with current surge on start.
    Crendon Chassis No.49
    Huddart FE428 + toploader

    Not listed in the Shelby Register.

  10. #10
    Join Date
    Aug 2007
    Location
    Bournemouth
    Posts
    697
    I have a Holley but I have locked out the choke to permanently off. First start of the day I give four or five pumps and she starts right up. After about thirty seconds to a minute of tickling the accelerator to keep her going she achieves self sustaining idle and I crack on with the day. Been like that since 2004 when I finished the build with no issues.
    David.

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

    Wessex region caretaker rep.

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