Zenith Carb / fuel pump issues - hard to diagnose

Discussion in 'Mechanical Hints/Tips' started by Doug, Apr 7, 2017.

  1. Doug

    Doug Member

    Hi all

    I wonder if you can help - our 1725c zenith carb Commer has an intermittent problem:

    Drive along.. all seems ok.. then he cuts out.
    It's not an immediate thing, kind of grunts along for 100 feet or so then dies.

    Checked spark (I thought it was the condenser) - all ok. Condenser replaced anyway as they are voodoo.
    So don't think its electrics.

    Fuel line checked, all ok - not leaking air, not blocked.
    Fuel pump dismantled and cleaned up. I had alerted them of the 'snakeskin' problem- doesn't appear to be the case.
    Carb dismantled and cleaned.
    Note: it's not me doing the work: it's a local garage, but they're a bit stumped.

    At one point this was happening about every quarter of a mile, and running the engine on the starter motor for a while then leaving on tickover seemed to get him running again for a bit.

    The garage have fitted a new accelerator pump, cleaned the fuel pump, cleaned the carb, and now he seems better but did it again after about 20 miles.

    Are there any 'usual suspects' to check for these symptoms?
    Any suggestions as to how to diagnose further where the problem is ?

    thanks in advance,

  2. PaulJL

    PaulJL Well-Known Member

    Are you sure the fuel filter isn't blocked or the tank outlet gunked up?
    Back in my war fighting days I had a similar problem with a Scorpion tank...(4.2 jag petrol) Turned out it was the fuel hose lining coming away and was flapping down causing it to block the hose. I took the hose off and refitted it the other way round.... Got the boys back to camp with no other issues.
  3. Doug

    Doug Member

    Wow ! Never thought i'd share issues with a scorpion tank !
    hm i guess it could be something like that although the fella at the garage says he's checked the line and all is well.
    After posting this, decision made to convert to weber carb (bolt-on conversion) just cos the zenith seems troublesome, but i have an eye on tim's SU conversion when the time is right
    PaulJL likes this.
  4. jimberlake

    jimberlake Well-Known Member

    Does sound very fuel blockage symptoms.
    Doug likes this.
  5. PaulJL

    PaulJL Well-Known Member

    I had a weber.. Binned it for an SU... The difference is amazing. I went from 20mpg to 35+ish with more power
    Doug likes this.
  6. Doug

    Doug Member

    Yeah we'll be in SU- land when i can get the bits together. This is more a defensive move to get something that works..
  7. Panky

    Panky Administrator Staff Member

    It does sound like fuel starvation. Get them to try hooking up a temporary fuel supply and see how that goes.

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