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"new" Mikuni fuel pump plumbing

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crkckr

Well-Known Member
Joined
Apr 26, 2016
Messages
58
Location
Warrenton, MO
I've been having trouble with the Rotax 447 on my Firefly not wanting to idle below about 2400 rpm and I also have to directly inject fuel into the carb to get it started, which was not the case previously. So, I bought a new Mikuni from Spruce and it arrived... with 3 ports instead of the 2 on the old one. I've done a lot of searching on the 'net and have found nothing but confusion! I have seen the pump referred to as both a vacuum and impulse pump (on the same site!) and variously as one or the other on several other sites (I suppose it could be called both but most of the actual references I've seen call it a pulse pump). I am at a loss as to how to plumb the center (vertical) port... I've seen everything from plumbing it back to the tank, into the carb (although there's no place on the Bing I can see) and even seen it plugged up completely on one site. And while this pump is advertised at having a weep hole, it does not, at least in the place it's usually shown, a small dimple on the front of the pump case (I'm just guessing the 3rd port takes the place of the weep hole but I can find no obvious reference to that). Does anyone actually know with certainty what the 3rd port is for and how it's supposed to be plumbed? Also, I've seen several references to the orientation of the pump body - none of which agree with each other! Is it supposed to be with the 3rd port up or down, and the body vertical or horizontal? Or does it not make any difference?
TIA,
Cheers,
crkckr
 
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