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  1. #1

    Default New exhaust now very rich

    I recently installed a 2.5 inch full length exhaust with magna flow cats (punched out) and magna flow mufflers. With BBk h pipe. Engine runs super rich now, feels down on power and fouls spark plugs. 1 3/4 full length headers. Brand unknown

    Ran amazing with open headers. Question is do I need to re jet carburetor or increase exhaust size? Jetting is cheaper to change.

    Engine combo is a 363ci
    Afr renegade 195cc
    750 double pumper holley

    Made 570hp and 520fp on engine dyno

    Sent from my SM-G950W using Tapatalk

  2. #2

    Default

    First, one situation (exhaust system change) is highly unlikely to have anything to do with the other (a new plug-fouling rich condition... unless everything was plug-fouling rich during dyno/"tuning"...). The question goes quite a bit deeper than just changing jetting (in a Holley 750 DP, those should be #70 primary and #80 secondary) or exhaust pipe size increase (?). Problem is likely a simple one, and carburetor related... (jetting really only has affect on deeply open or wide open throttle blades, air:fuel mixture-wise)

    Runs super rich where/when? Everywhere? Wide open? LIST-4779-X? When was the carburetor last looked over and/or tended to (all air bleeds clean and clear, float levels checked/set, mixture screws adjusted for lean-best idle, idle speed settings set, etc.) or gone through, rebuilt? Leaky power valve diaphragm or gasket?...

    What's the ignition and how is that configured? (Initial, "curve", total, vacuum advance?)...
    Mike
    1986 Mustang convertible ---> BUILD THREAD
    Past Fox-chassis "four eyes":
    1983 Mercury Cougar LS
    1986 Ford Thunderbird ELAN
    1980 Capri RS Turbo

    Work in progress website ---> http://carb-rebuilds-plus.boards.net/

  3. #3
    FEP Senior Member gt4494's Avatar
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    Nov 2004
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    Default

    Without cats you will definitely smell the gas out the tailpipes until it warms up. even then there will be some smell. Not like the original rotten egg smell from cats.
    "If you can't explain it simply, you don't understand it well enough."
    Albert Einstein

    1984 20th Anniversary GT350
    Almost "Stock"

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