| Author | Message | ||
     The4ork |
i know its used for a tuning aid, but what exactly does it do, does raising it provide a richer mixture quicker? or does it make the mixture richer at all times when its raised above the seated position? also, the slow jet, is it only being used when the needle in the main jet is seated? im just wondering for my own knowledge. | ||
| Daveswan |
This is a nice link to have which explains each of the circuits and how one effects the other. The chart at the top gives a visual representation of how each of the pieces interrelate and the text provides the overview. It's not for a CV carb specifically, so don't try and go by what they show for float height and adjustments. I think I have a link someplace for the CV, but there's similarity as to what's going on so you can get the basic idea. http://www.keihin-us.com/am/_media/pdf/slide_valve .pdf (Message edited by daveswan on August 15, 2010) | ||
| Sanchez |
The Mikuni HSR42 tuning guide has some good info and pictures as well: http://www.mikuni.com/pdf/hsr_tuningmanual_021003. pdf | ||
| Erwin8r |
..but in summary, raising the needle richens the "middle" a little bit. At full throttle, the carb should be all main jet... At near-closed throttle, the carb is on the pilot or slow jet... | ||
| Sloppy |
Key thing with carbs is to understand that they work in additive stages (pilot, slide cut away, needle, needle jet, main). Also you need to distinguish if you have a CV carb (constant velocity) where needle position adjusts bases upon ENGINE load or a slide carb where needle position is dependent upon THROTTLE position. Step 1 - identify carb. Step 2 - READ!!! Note - if the engine and carb is stock, then all you need do is clean it and put it back the way you found it... | ||
| Jayvee |
The needle is tapered. When it gets thinner, as it rises in it's orifice, more of the orifice being open causes more gas to sucked up from the float bowl. The angle of taper controls the rate at which the area of available orifice (hole in the needle jet) grows when the throttle is twisted. By shimming the needle up, it pre-moves the needle up, to where it's now higher for the same throttle position than it was before. More orifice area available earlier, more gas added to the mix earlier, richer mid-range. Everything else stays essentially the same. Something like that. |
