I've been running motorcycle carbs for a few years now. All you need is a fuel pressure regulator to limit it to 1.5 psi. I run a little bit less just on 1 psi. The float needles will seat at upward of 3 psi but it varies from carb to carb, stick to 1.5 and it will be fine.

As for the description flat slides are generally referring to mechanical operation to lift the slide versus a CV carb which uses a diaprhagm to lift the slide both types could have a "flat slide".

The CV type are a bit more,user friendly, a decade ago i ran a Yamaha 1000 powered single seat sports racer and it used CV style downdraft carbs which worked quite well. On my 1200 coupe I run the Keihin FCR flat slide carbs and they also are fantastic, as an motorcycle racer I am biased but I think bike carbs are better made and offer more performance

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