308 carb Still running rich/ideas? and plugs have carbon build up | FerrariChat
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308 carb Still running rich/ideas? and plugs have carbon build up

Discussion in 'Technical Q&A' started by 308GTS, Apr 26, 2004.

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  1. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    2,223
    TN
    #1 308GTS, Apr 26, 2004
    Ok, my 308 is still running rich. I was wondering if anyone has any ideas. The car runs great but I don't think running this rich can be good for it.
    Any good ideas would be appreciated. Here are the specs:

    78' 308
    Crane XR700s and PS20 Coils
    New NGK Plugs (BP6ES)
    New Wires. Caps rotors have limited miles on them and look good.
    Carbs 135 mains, 55 idles, 220 ACs
    Just rebuilt carbs and all cylinders are firing, I have found no air leaks

    Here is what I am not to happy about. I am flowing 4 1/2 KG/Hr but it is too rich. I can lean it out with the mixture screws but to get the plugs to look toasty brown I will flow 6-1/2 kg/hr. Why so much airflow to get the plugs to look toasty brown? So getting the plugs to be a nice brown is achievable but it is flowing too much air. Any thought would be appreciated.
     
  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,932
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #2 Steve Magnusson, Apr 26, 2004
    Even the 4.5 Kg/hr seems a little high if your idle timing is set to ~7 deg BTDC and 1000 RPM -- IME more like 3.5 Kg/hr at that RPM and timing (but there's always some difference in absolute calibration of different instruments).

    When you say "all cylinders are firing" does that just mean that you've verified the spark occurs or that each cylinder seems to be contributing the same amount of power at idle (i.e., at idle when you unplug each spark plug one at a time to intentionally "kill" its cylinder, do you note an equal drop in RPM and a similar change in acoustic note)?
     
  3. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    2,223
    TN
    #3 308GTS, Apr 26, 2004
    Yes. I have verified spark at all cylinders and also pulled the plugs manually while the car was running one at a time and noted an equal drop within each cylinder.
    I did have a problem with one cylinder dropping out every so often but that was fixed when the carbs were rebuilt.

    Is there anything else that could cause this. 7 kg/hr is very high but my plugs will not be a nice brown without the mixture screws being turned in and therefore I have to raise the idle which brings the flow up to 7 kg/hr.

    Yes, my idle speed is 1K with timing set to 7 deg. Adv. at idle. I have checked my advance to throughout the entire range and it is correct.
     
  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,932
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #4 Steve Magnusson, Apr 26, 2004
    Sorry -- I can't add anything. The power difference from a cylinder running very lean or very rich to operating at its best power A/F ratio is only like 10~15% so I don't see how you can have two conditions with a 40~50% difference in airflow yet be at the same RPM (if all cylinders are functioning in both conditions).
     
  5. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    2,223
    TN
    #5 308GTS, Apr 26, 2004
    Well, ~ 4 turns out or a little more gives a nice brown appearence on the plugs. I am at ~ 5 turns out now so unless my Synchrometer is reading false I am not sure what to look at. Thanks.
     
  6. cavallo_nero

    cavallo_nero Formula 3

    Nov 3, 2003
    1,707
    colorado
    Full Name:
    Giovanni Pasquale
    #6 cavallo_nero, Apr 26, 2004
    maybe pull the airhorns on each carb and check the float height. 48-49mm is OK.
    john
     
  7. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    9,742
    #7 Mitch Alsup, Apr 26, 2004
    Make that 2%-3% from lean (leaner than 14.2) to best-power (13.2) to rich (richer than 12.9).
     
  8. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
    4,367
    NY
    #8 Steve King, Apr 26, 2004
    I idle at about 4kg at 1000rpm and pertronix ign and full 12v Bosch blue coils. Run disz's at 7 dbtdc and have NGK BP 5 ES plugs. A/F mixture screws are 6 -6 1/2 turns out on all carbs. Never took the carbs apart yet so assume mains , idles and AC's are stock for my 77. Idles a little rich but cranks when you jump on it. Also runs fairly cool at maybe 175 degrees. Hasn't been warm enough here yet to get engine temp to 195. Usually in August.
     
  9. 308GTS

    308GTS Formula 3

    Dec 27, 2001
    2,223
    TN
    #9 308GTS, Apr 26, 2004
    Thanks for the info. Mine runs great. Get on it and it goes. Runs really cool in the summer even with the a/c on it never gets above 195. Maybe I should leave it alone. I just didn't want it to be too rich. Thanks Again.
     
  10. Steve King

    Steve King F1 Rookie

    Feb 15, 2001
    4,367
    NY
    #10 Steve King, Apr 26, 2004
    try using NGK 5's instead of 6's . 5's are hotter and run cleaner. No effects on highway driving. I get arount 17 mpg on long rides
     
  11. bernardo66

    bernardo66 The Crazy Cat Man
    Lifetime Rossa Owner

    Dec 14, 2003
    26,591
    Montreal Canada
    Full Name:
    Bernie
    #11 bernardo66, Apr 26, 2004
    When I bought my 78 308GTS, I showed it to a friend of mine who worked for the original Ferrari dealer in Montreal, for over 20 years. He gave the car a once over and mentioned that the carbs on the 308's were set up to run a little rich. In fact, he suggested to me that I change my plugs annually, and not worry if the car ran a little rich.
     

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