Well traveled topic - are my carbs kaput?

Discussion in 'Mech Tech' started by Nicolasticity, Jun 2, 2024.

  1. IMG_3140.jpeg IMG_3134.jpeg IMG_3138.jpeg IMG_3137.jpeg IMG_3136.jpeg IMG_3135.jpeg After an eight year body resto Chuggs goes for its first spin. Brakes spongy running erratic….
    Got some fuel and then engine leaned out backfired and stopped. Would start and run but no power and then stopped. Leave it for 30 mins and it ran but no power really so limped the mike home.
    Before the restoration I knew throttle bodies leaked using tge brake cleaner test. Carb is 2.5 turns mixture but 1 turn idle (didnt set them up before the spin)
    Did a pressure test and get 130 to 140
    Psi which seems ok? and in 10%.
    Plugs are all cold and sooty…
    So is it time for new carbs? Is there a Bristol guru to advise as a 2ltr Type 4 engine seems a complex beast.
     
  2. davidoft

    davidoft Sponsor

  3. It has a new coil and electronic ignition new leads and distributor cap? Is it an earth issue.
    Should I get it hot and see how far the spark will jump?
     
  4. Have you balanced the air flow in the two carbs?
     
  5. I tried but tomorrow I will start from scratch - very tempted just to give it to a tuner locally.

    I dont have any gauges so used a tube and ear…
     
  6. Stock carbs?

    I would give the carbs a good reset first.
    Check float levels.
    Balance.

    Bit hard to see but are plugs sooty or oily?
     
  7. mikedjames

    mikedjames Supporter

    Usually the stops with a bang is ignition related.

    The distributor jumping up and losing timing because its sort of engaged 180 degrees out, which it can.
    Then the timing is off after that..

    Loose wires.

    Electronic module could be faulty.

    But as its the first drive out its probably something fell off.
     
  8. Stock carbs and plugs are sooty not wet
     
  9. Have a uni syn coming to balance carbs. Floats good and both carb levels same. Noticed that the RH slave carb has a hole in side as pic. Is that right?

    is this where the mixture adjuster should be..
     

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  10. Purchased it in April 2016 for Glasto - demo was great but halfway home it started missing etc and stopped a few hundred meters from home. Eventually got it going but on route tp campsite in Dorset it broke down at Gordano (8 miles) and AA back home. So I took it apart and restored it but didnt touch engine. I have never had it running properly here but now retired its time.
     
    mikedjames likes this.
  11. Don't just randomly fiddle with the carbs or you'll never get them set up correctly. The set up procedure needs to be done in the correct sequence, it's a bit of a faff but entirely doable.
    The Itinerant Aircooled website has an excellent guide to set up, I would recommend reading it and as much other material as you can before tackling them:thumbsup:
     
    mcswiggs, snotty and Nicolasticity like this.
  12. Yep Im on it!
     

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  13. Should point out that it's written around US spec carbs which are very slightly different to European ones (emissions related stuff) but the general principles are the same.
    Also before touching the carbs check and adjust valve gaps, points, plug gaps and ignition timing.
     
  14. Zed

    Zed Gradually getting grumpier

    I think there should be a pinch bolt in that hole to secure the venturi.
     
  15. mikedjames

    mikedjames Supporter

    AHA! The ignition module fried and it still doesnt like you 8 years on.
     
    Nicolasticity likes this.
  16. Quick update now I have a flow meter….

    At about 1100rpm RH carb Flowmeter was adjusted to read max. All the LH carb managed is the lowest indicator mark…

    Not surprised its popping and wheezing

    Soon as it stops raining…
     

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