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Thread: Mikuni jet sizes

  1. #1

    Mikuni jet sizes

    Kind of an odd request, but anyone have VM32s or even 34s that feel like doing me a favor? I know Mikuni sizes their jets based on flow instead of bore and was wondering if anyone could measure the bore of the main and needle jets for me.

    The reasoning behind this is that I have some Bing Type 84 32mm round slides that I've been toying with the idea of adapting them to my R90/6. I have quite a few Bing mains, needles, and pilots of various sizes to play with and tune on my own, but figured I'd at least use Rocky Point's Mikuni jetting as an initial baseline. According to the Mikuni jetting chart the VM32s use a 200 size main jet, a P2 needle jet, and a 35 pilot

    I don't have any problem with the type 64 cvs that are on it and if I can't get the jetting right on the 84s I'll continue going stock (all 3 of the 84s I have on my shelf cost less than one mikuni, and they don't cost anything to keep on the shelf), but I'll be lightening the flywheel, maybe dual plugging the heads, and switching to high-compression pistons this winter and have been thinking of experimenting with velocity stacks and slide carbs as I've heard some good things about the Mikunis with this setup.

    Any help would be appreciated. If I decide to go this route after I get all the other work done I'll be sure to post back with my findings

    EDIT: just found a chart for the needle jet which indicates P2 is a 2.66, still could use measurements for the main
    Last edited by Typ181R90; 11-22-2011 at 08:17 AM.
    // 1975 BMW R90/6 (cafe'd) // 1957 BMW R60 (in pieces) // 1967 Aermacchi/H-D Sprint 250 SS (custom special) // 1967 Moto Guzzi V700 (current restoration)

  2. #2
    Small road corner junkie pffog's Avatar
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    Apr 2006
    WNY, Further fron NYC, than 6 entire states!
    Personally I don't the bore similarity alone will have any correlation to the mixture between completely different carbs. So many other variables like venturi ratio, needle seat and needle, fuel level compared to venturi etc.

    Bottom line is you are looking for the proper MIX (approx 14:1 by weight). All engines live around this ratio for optimal combustion.

    I would use numbers other Bing carbed people are using. On top of that main jet is only fully in play at WFO throttle openings and high RPM's so 99.5 % of the time it has a lot smaller influence than the needle and needle seat characteristics and relation.

  3. #3
    Oh I know and I'm not in any way trying to copy the mikuni jetting, just curious how they're jetting theirs. I realize I'm going to have to play around with the jetting and needle and do hands on testing but the type 84 is more similar to a vm32 than a Bing Cv so I figured I'd start there and then go. Fwiw 2.66 for the needle jet is quite close to the 2.68 on the stock type 64s
    // 1975 BMW R90/6 (cafe'd) // 1957 BMW R60 (in pieces) // 1967 Aermacchi/H-D Sprint 250 SS (custom special) // 1967 Moto Guzzi V700 (current restoration)

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