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Easiest carb rebuild/tuneup I ever did

Discussion in '308/328' started by AZDoug, Oct 13, 2009.

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  1. AZDoug

    AZDoug Formula 3

    Jun 17, 2009
    1,606
    Along the Verde , AZ
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    Doug
    #1 AZDoug, Oct 13, 2009
    As mentioned yesterday the dyno guy told me the carbs should be gone through to get rid of the crap that was probably making it run too lean and have flat spots.

    I figured I would try some fuel system cleaner, so i bought two bottles of STP fuel system and carb cleaner and added it to about 10 gallons of gas in the tank.

    Drove car about 8 miles, let it sit 20 minutes and drove another 5 miles, well, all the throttle mashing hesitation and lean back firing is gone and the car accelerates much better, I guess this stuff really does work.

    For those bringing cars back from storage, I think it is a cheap $5 fix.

    I did run about 8 gallons of gas thru the car prior to adding this stuff.

    Doug
     
  2. RichardAguinsky

    RichardAguinsky Formula Junior

    Nov 12, 2007
    478
    Palo Alto, Californi
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    Richard Aguinsky
    #2 RichardAguinsky, Oct 13, 2009
    On all my other cars, I tried several brands of carb and fuel injector cleaners. The only one that made any noticeable difference was the Techron Concentrated Carb/Injector cleaner and the BK-44. Though I had a few comments that these are corrosive if over used. I was adviced in using Lucas fuel conditioner, which I do not notice any difference what-so-ever.
     
  3. AZDoug

    AZDoug Formula 3

    Jun 17, 2009
    1,606
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    Doug
    #3 AZDoug, Oct 13, 2009
    I always thought this stuff to be somewhat snake oil, but figured it was a cheap experiment.

    Note I did add it at about 4 times the recommended concentration, but It must have dissolved or loosened the varnish that no doubtedly accumulated in the carbs over the years.

    I ran into a similar situation on a Holley many years ago on an infrequently operated car, the car just wouldn't run right when i brought it back to life, it was too lean on acceleration,and lean in general, so I changed the jet sizes to larger until it ran, not thinking that there may be other problems.

    Well, after operating the car everyday for about 3 weeks, it was running way too rich, I had to go back and rejet it leaner due to passages opening up again and flowing gas like they should.

    Doug
     
  4. RichardAguinsky

    RichardAguinsky Formula Junior

    Nov 12, 2007
    478
    Palo Alto, Californi
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    Richard Aguinsky
    #4 RichardAguinsky, Oct 13, 2009

    I had lots of fun in the past rebuilding carburators and changing points.

    The venturi in the carburator creates vacuum. The vacuum sucks gas through a calibrated size hole in the jet. The larger the hole, the more gas goes through it and vice versa. The jets are calibrated to an a/f of about 14.7 to 1. A smaller jet lowers the flow of fuel, hence there is more air than fuel (lean). On the other hand, a larger hole sends more fuel than air (rich).

    If the jets have gunk in them, the hole is smaller, hence the flow of fuel is less and the mixture is lean. This is fixed with a solvent that can remove the gunk in the jet, opening up the jet to its original size.

    The body of the carburator also has holes to allow extra fuel as the throttle opens. These also get gunked up. A solvent will disolve the gunk.

    By putting larger jets, the mixture is richer, the car runs faster, but you need to make sure you do not overheat the cats (fixed by gutting them).
     
  5. flyngti

    flyngti Formula 3

    Jul 16, 2009
    1,246
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    Eric L
    #5 flyngti, Oct 14, 2009
    Doug, how well did your engine run when you first started it? We're in a similar boat with recently starting a carb'd 308 after extended storage. Mine seems to run surprisingly well, although I can't drive it yet. During warm up (about the first 5 minutes), I can barely touch the throttle without hissing and spitting out the carbs. After it warms up, it revs smoothly with the occasional carb spit. It does seem to run better each time I start it so it's probably still blowing out gunk in the system. I'll try some carb cleaner additive to see if that helps.
     
  6. AZDoug

    AZDoug Formula 3

    Jun 17, 2009
    1,606
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    Doug
    #6 AZDoug, Oct 14, 2009
    Exactly what mine did. You are running too lean, most likely due to varnish.

    I would make sure the car is driving before I added the carb cleaner so you can use it up in a week or so and not let it sit in the tank for weeks, IMO.

    Doug
     

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