> Thinking some more about Dave's suggestion for manifold vacuum. >
   ThatÂ
    > should work, except at wide open throttle where there is not muchÂ
    > pressure drop in the manifold.Â
   Â
    >Â
    > That's why carbs have venturis toÂ
    > draw fuel out by dint of lower pressure in the venturi, even at >
   WOT.Â
    >Â
    > Anyway, manifold vacuum might work -- won't know until we try it.Â
    > But its a moot point since these Mikunis have a fitting ready to >
   go...Â
    >Â
    > Regards,Â
    >Â
    > Gordon.Â
   Â
   ***** Hi Gordon,Â
   Â WOT is usually takeoff and climb, where we want "Full Rich"Â
   Â
   Thinking some more about mixture control for the Mikuni; I think IÂ
   prefer the "in- carb" mode; the carb leans itself and the failureÂ
   mode is back to "normal" ie , no lean.Â
   There is something natural about balancing venturi pressure againstÂ
   fuel pressure within the carb that appeals to me. And all for 160Â
   bucks!Â
   Â
   Bill Jepson,Â
   we have spoken at length on carbs, and "things" these past few years;Â
   i would appreciate your valued comments.Â
   BR, Dave McCÂ



   WOT is not necessarily where you want full rich.Â
   Usually people run WOT at 7500 feet and above where power isÂ
   down to 80% or less. You need to be able to lean it there.Â
   Â
   In fact you should be able to lean it an any altitude so IMHOÂ
   a leaning feature is mandatory. However if fuel burn and MPGÂ
   are not issues with one then one could go with the stock carb.Â
   Â
   -- Paul Lamar ...No rotor no motor.Â



   Dave and Group,
   The carb concern is that we want full rich at WOT at takeoff, but
   we need to lean sagnifigantly above about 3000' and certainly above
   4000'. The advantage of a vacuum slide carb, (or constant velocity
   carb)
   is that the lift of the jet needle is caused by the airflow. In less
   dense air
   the carb is "self-leaning" to a certain extent. That is why they use
   them
   on all the ultralite 2 cycles even though the straight slide throttle
   usuallyÂ
   produces max HP at sea level. The "flat slide" carb is a design that
   reallyÂ
   mimics a slide throttle. The sides of the venturi are generally faired
   intoÂ
   the sided of the venturi's bore. There is still a reduced diameter
   venturi,
   but the lead-in and out are carefully contoured to allow max airflow
   for aÂ
   given diameter. Great for power, but crappy for high altitude unless you
   stay a size down to keep up the vacuum signal so they will still
   pull fuel
   from the float bowls. The vacuum-slide carb is a natural for icing
   BTW. The
   openings are small and they (VSC's) all have a butterfly downstream
   of the
   slide that is the actual throttle control. The vacuum slide acts solely
   due to
   vacuum and isn't physically connected to the throttle butterfly.

   Paul Dave et al, Mikuni used to have available remote jet kits that
   replaced
   the center throttle cap and replaced the main jet. If you want to
   run carbs
   this would be "the way to do it" as the system could be replaced with a
   needle
   valve that would allow leaning. The runs of tubing can't be long, less
   than 3" if
   memory serves, but that would be enough to allow replacement with a
   variable-
   orifice system.
   Bill Jepson


FYI:  A lot of "snowmobilers" I know put a vari flow valve on their
carbs so they don't need to jet them all the time.  Check out this
site:  http://www.holtzmaneng.com/ and look under vari flow (they also
have kits for temperature compensation).  This can be used to adjust the
fuel mixture.

Cheers,

Burck



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