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Thread: Tuning a 450cc single cylinder engine with plenum and restrictor

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    Tuning a 450cc single cylinder engine with plenum and restrictor


    My name is Constantine and I'm from the University of Hawaii FSAE team. We are currently trying to tune our Yamaha 2012 YFZ450R motor with a
    carbon fiber plenum. We are using a Vortex X10 ECU and a standalone A/F monitor. Our maps are all based off tps and we have control over fuel,
    ignition timing btdc, and end fuel timing. It starts pretty good and we have been able to get it to idle well at around 2200 RPM and it revs up nicely
    with good throttle response without any surging or RPM holding.

    The only problem is that it dies after revving from idle on the way down. In other words at a steady idle when throttle is blipped up to ~50% tps momentarily
    it will rev up to ~8000 RPM and then die when revving back down to idle. It won't even hold more than a fire or two at idle RPM before dying unless throttle
    is blipped again by catching it from falling below idle RPM.

    We're thinking that this is because when the rpms are falling as the throttle is nearly closed it creates a vacuum in the plenum chamber and not enough air can
    be supplied to support the fuel being injected at that rpm. We tried reducing fuel around 2k-4k RPM but that didn't seem to help much.

    Could we just need a bigger plenum? What are your guy's thoughts or experiences with tuning a similar setup?

    Thanks in advance.

    Last edited by dpapazach; 04-24-2018 at 05:06 PM.

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