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Thread: Mixture questions

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  1. #1
    marlinspike is offline CHR Member Visit my Photo Gallery
    Join Date
    Aug 2006

    Mixture questions


    I'm able to feel when an engine is lean at full throttle that slight vibration is makes, but is there a point at which it's too rich and that causes vibration at full throttle? I don't mean so rich the engine is obviously bogged down, but some point just after the ideal mixture. I always thought of mixture is rich has no negative impact (other than loss of power) up to the point that it starts to dilute your oil, but I've been tuning my mixture (the old school spark plug way) and it seems like the is the point at which the car runs smoothest (i.e. leaner or richer will be rougher at full throttle) but a new plus with 2 passes on it still won't have a full ring of color on the base of the insulator. I need to get somewhere I can time it or on a dyno I guess, but until I get more money my deserted road technique has to be used.

    It seems like the richening, the one that makes it not as smooth on full throttle, gives it a sizable boost in the lower rpms (at the smoothest mixture, the best launch is achieved basically by just planting my foot from a stop - 2.47 gears and a 4 speed auto - but at the richer mixture if I do that the wheels will just spin and spin and spin), but slower at higher rpms (say beyond 4k or so) and basically the same time 0-60.

    The car is mechanical fuel injection (Bosch K-jetronic aka CIS, not to be confused with KE-Jetronic aka CIS-E) with a vacuum enrichment (though, I can't imagine the rpms impact that because I would think full throttle is always kicking in the vacuum enrichment). There's one thing known to be wrong with the fuel injection: the fuel pressure from the warm up regulator is a little low, so what's the right mixture at idle is lean at full throttle and to richen it from the main adjustment to get it better at full throttle means too rich at idle (I can adjust that...I just have to make a tool to pull up on the valve of the warm up regulator first).
    Last edited by marlinspike; 10-04-2008 at 11:53 PM.

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