Air fuel ratio
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Air fuel ratio

  1. #1
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    Default Air fuel ratio

    I hooked up an AEM wideband setup in order to monitor/tune my engine. 476 BBC, 9-1, aluminum oval port heads, dual plane intake, 850 quick fuel marine, Berkeley jg A- impeller fresh from MPD, 5400rpm wide open.

    at around 3400-3600 I'm bouncing between 12.1-12.6 on the meter, wide open it was between 13.3-13.6. Seems like I can go leaner at cruising rpm, wide open seems ball park. Is it normally for the ratio to bounce around like that? It's completely erratic, almost hard to catch the reading before it bounces a little higher or lower. But engine runs damn good andcruises smooth as butter. Thanks!

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  3. #2
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    Quote Originally Posted by nos1967 View Post
    I hooked up an AEM wideband setup in order to monitor/tune my engine. 476 BBC, 9-1, aluminum oval port heads, dual plane intake, 850 quick fuel marine, Berkeley jg A- impeller fresh from MPD, 5400rpm wide open.

    at around 3400-3600 I'm bouncing between 12.1-12.6 on the meter, wide open it was between 13.3-13.6. Seems like I can go leaner at cruising rpm, wide open seems ball park. Is it normally for the ratio to bounce around like that? It's completely erratic, almost hard to catch the reading before it bounces a little higher or lower. But engine runs damn good andcruises smooth as butter. Thanks!
    It's not unusual. Unless the water is perfectly smooth, there is some interaction caused by the boat moving around(bouncing even slightly). Another factor, depending on how your throttle is set up, but if it is a foot throttle, the foot can bounce a little on the peddle.

    When it's wide open, your throttle is planted hard and is held steady.

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    That makes sense! Thank you.

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    Finally got all the small stuff worked out on my 21’ open bow and maxed out my 65mph speedometer. Cruising I’m at 12.7 and wide open I’m at 13.1 air/fuel ratio. Should I try to get my wide open air/fuel closer to 12.5-12.7 or just leave it? I would also like to get my cruising air/fuel a little higher for fuel efficiency. Was think of going down a jet size on primary’s and up 2 jet sizes on secondary’s. Any thoughts?

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    for a n,a engine i shoot for 12.5 afr at wot.slightly leaner at part throttle.

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    Quote Originally Posted by buck28 View Post
    for a n,a engine i shoot for 12.5 afr at wot.slightly leaner at part throttle.
    Agreed, I like mid 13s for cruise, keeps plugs and oil cleaner plus saves fuel for the hold my beer moments😁

    Dare to be different, if it turns out great you can claim you planned it that way.

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    If you have accurate RPM readings tune it for the most RPM at wide open. Staying in the safe AF range
    If For Some Reason I Do Something Worthy Of Recognition. God Provided The Ability And Deserves The Credit.


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