Replacing carb lead plugs | FerrariChat

Replacing carb lead plugs

Discussion in '308/328' started by DANCER308, Jan 10, 2015.

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  1. DANCER308

    DANCER308 Formula Junior

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    1979 308 GTS.

    Decided to replace the lead plugs on the carbs. After 35 years, some have started weeping. In order to avoid anything left in the passage ways, I removed all jets, needles and emulsion tubes. I needed to know where all passage ways started and ended. After removing all lead plugs, I shined a light down each passage to know that all was cleaned out, very very important.

    The bore is 2.9mm. Increased bore to 3.49mm(9/64” drill bit) for a depth of 4.2mm, this leaves a shoulder for the lead shot to seat against. I used 4.52mm lead shot(bb’s). Removed old plugs with a small screw and pliers. Set the lead shot with a 6.14mm punch with the end hollowed out to leave a raised bump on the lead shot. Used a 4.62mm punch to push in the bump and flatten the lead shot. Used my trusty swiss army pocket knife to slice off the lead ring left by the small punch.
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    Last edited by a moderator: Sep 7, 2017
    DANCER308, Jan 10, 2015
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  2. Peter

    Peter F1 Veteran Owner

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    Thanks for posting the procedure and photos!
     
    Peter, Jan 10, 2015
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  3. Pero

    Pero Formula Junior

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    I haven't even seen the lead plugs on my carburettors. Why is the hole there in the first place, since it is plugged? And, what problems can a leaking lead plug cause?

    /Peter
     
    Pero, Jan 11, 2015
    #3
  4. DANCER308

    DANCER308 Formula Junior

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    The passage ways allow the fuel in the bowl to get to various places within the carb. These passage ways are either factory drilled or cast into the mold, so one end of the passage must be sealed. A leaking plug can either allow air to leak into the carb or allow fuel to leak out onto the hot engine. Both situations are bad, especially the latter.

    Dan
     
    DANCER308, Jan 11, 2015
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  5. DANCER308

    DANCER308 Formula Junior

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    You can see signs of leaking by fuel stains around the plugs.
     
    DANCER308, Jan 11, 2015
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  6. Pero

    Pero Formula Junior

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    Thank you for a very clarifying amswer. I really didn't know and will check the plugs next time.

    /Peter
     
    Pero, Jan 11, 2015
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  7. DANCER308

    DANCER308 Formula Junior

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    You're welcome. If you look at the last picture just to the right of the plug, you will see another plug with fuel stains around it.
     
    DANCER308, Jan 11, 2015
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  8. Pero

    Pero Formula Junior

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    Yes, I can see that. Useful info, great. And thanks for the photos!

    /Peter
     
    Pero, Jan 11, 2015
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  9. DANCER308

    DANCER308 Formula Junior

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    Be sure to check for leaking new plugs before reinstalling the carbs. I placed the carbs on brown paper and filled the bowls about half way with gas. After the sat for about 15 minutes I noticed that one of the forty some odd plugs was leaking. Replaced that plug and was good to go. The upper plugs can't be checked until back on the car with just the fuel pump running. There is slso a plug in the carb top cover, one of mine was leaking.
     
    DANCER308, Jan 20, 2015
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  10. Pero

    Pero Formula Junior

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    Ok, thanks for the info. I really had no clue about this before.

    /Peter
     
    Pero, Jan 20, 2015
    #10
  11. bill308

    bill308 Formula 3 Silver Subscribed

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    Hi Dan.

    Are the 4.52 mm bb's from a sports equipment or gun store? 4.52/25.4=0.178 inches or caliber.

    Good job and nice write up.

    Bill
     
    bill308, Jan 20, 2015
    #11
  12. DANCER308

    DANCER308 Formula Junior

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    Bill,
    Hi. They are actually 4.57 mm, .180 in. I fat fingered the size. I got them from a man that sells ammunition. I didn't know they even made lead bb's. I was originally looking for a number 2 shot, 3.81 mm, .150. He said #2 was hard to find. The 4.57 mm works better because the 9/64 bit puts a larger shoulder further down in the bore.

    Dan
     
    DANCER308, Jan 20, 2015
    #12

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