Opinions on this please

[Sable]

Being mechanically challenged... I went to a web site called "how stuff works" and this is one of the links for tuning carbs... My first question is: is this accurate for trouble shooting carbs on a Vision, or is this for a more "mainstream" type motorcycle?

http://204.71.0.3/motoprof/moto/mcycle/carb101/carb101.html

Thanks for the help ;D

 ? ?~ John

[Lucky]

the theroy is correct, the figures 3-6 do not apply to Vision carbs.  Typical motorcycle carbs have slides, typical automotive carbs have throttle plates (or "butterflies").  Vision carbs are more like automotive carbs

they have this page: http://static.howstuffworks.com/mpeg/chainsaw3.mpg on "How Stuff Works" using a chainsaw carb as an example.

The basic principal for the Vision carb is you have a fuel source (bowls) an airway "restriction" called a venturi, and throttle plates that act like an "air-on, air-off" valve.

The venturi(s) are a section of the carb, in the airflow passage, where the cross section is smaller. squeezing air into a smaller space as it flows speeds it up.  same as if you squeeze the end of a garden hose, the water passes thru with greater force.

the throttle plates open & close, controlling the amount of air being sucked thru the venturies.  the engine (pistons) is really nothing more than a big air pump.

the bowls (and associated plumbing, jets, etc) precisley controll the flow of fuel.

Now comes the magic:
As air rushes past the venturi's, at certain speeds it will create different amounts of negative, or low pressure air.  the fuel passages are open to the venturi's and the air rushing past will suck fuel from them.  As the fuel is sucked into the air stream, it mixes with the air and atomizes. Liquid fuel does not burn well, but fuel mixed with air (oxygen) burns very well.

that's carbs 101 for today.
--Lucky

[Sable]

     Thanks Lucky.. what about Figure 7? Is that an accurate way to trouble shoot the carbs? That is, once you get the Pilot air screw and jet all set the way it needs to be, then if you have problems at idle to 1/2 throttle you should check the throttle valve, problems from 1/4 to 3/4 throttle check the jet needle and needle jet, and for problems from 1/2 to full throttle check the main jet? I don't want to seem like I am over-simplifing (sp) this, but this would make things a lot easier for me....
     I have read all the problems about the carbs and don't have the "know-how" to do it myself... I would like to take you up on your offer of coming down to your place for a day and learn everything there is to know about rebuilding them... before you get your harley ;D

~ John

[Lucky]

the Mikuni carbs on the vision have 2 basic circuts, idle & power. they overlap. the pilot air jet, pilot fuel jet and pilot screw comprise the idle circut, and the main jet controls fuel flow in the main circut.

opening & closing the throttle valves varies the pressure (fuel draw) of each circut. each circut only draws fuel at predetermined pressures. changing jets (different openings) changes the amount of vacume needed to draw fuel.  a larger fuel jet allows more fuel to pass, but requires more vaccume to draw it out.

in addition, these carbs, and most throttle valve carbs, use an additional circut called the accelerator pump.  this is a diaphram operated pump (with a spring loaded ball check) that draws fuel directly from the bowl, and sprays it directly into the venturi airstream. this is used mostly for sharp accleration, but since it's mechanicly connected to the throttle, it sprays every time the throttle is twisted.

email me your phone #, we'll see what we can work out for a day/time.
Lucky
lucky@xz550.com

[Sable]

Just fired off an e-mail to ya Lucky

Thanks,

~ John