Carb Needles

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gl_s_r
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Carb Needles

Post by gl_s_r »

Does anyone have a picture of the Factory Pro and HRC needles for the VTR... or some needles they can take the picture of?

Random I know but just wanted to see the difference between them and the usual standard and Dynojet ones..

cheers muchly
Why ask... sometime you just go to do it and find out?
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VTRDark
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Re: Carb Needles

Post by VTRDark »

If you can wait until Saturday I shall be removing carbs so can get some good close up pics and measurements of the factory pro needles. They start with a very narrow taper and then go fat without much if any gradient between changes and are nothing like the HRC needles. Not the ones for closed airbox use anyway, which are a similar profile to the original Keihin needles. I think you will find that they are all very different from each other but the HRC are the most similar to originals.

From memory and some pics grabbed from google.

Image
The factory pro needle is similar the one on the left in the above pic whereas the one on the right is similar to original Keihin.


Image
The above is the HRC jet kit for Firestorm. Note the two types of needles, one for open airbox or ram air and one for closed airbox. The leaner of the two is for closed airbox running race filter. It has a fatter midrange with smoother transition than the factory pro.

(:-})
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lloydie
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Re: Carb Needles

Post by lloydie »

Image

Factory pro and standard
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gl_s_r
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Re: Carb Needles

Post by gl_s_r »

Thanks chaps... really quite different then.

No need for measurements Carl, just curious to the amount of different needles out there and people ways of looking at the fueling differently.. so are the HRC profiles different to each other for the ram-air vs standard airbox??
Why ask... sometime you just go to do it and find out?
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lloydie
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Re: Carb Needles

Post by lloydie »

I know hrc do two needles .
One lean for full air box and one rich for open top air box .

Or is it lean one for when you block the main air tube off and the other when you don't ?
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VTRDark
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Re: Carb Needles

Post by VTRDark »

Or is it lean one for when you block the main air tube off and the other when you don't ?
Well that's the thing with the HRC kit there are very little instructions as such and they presume one knows what they are doing. It's lots of R&D and dyno time plus real world testing.

Here's the HRC needle instructions:

For needle selection the kit is set up for three (3) intake options.
a) Full Race Air Filter
b) No Air Filter
c) Ram Air

Start with the "lean" needle unless you are running option b or c then the "rich" needle will be used.

Needles on the 3rd clip (or middle) with one (1) .5mm shim on the front needle and two (2) .5mm shims on the rear\

:Shrug:


It is very interesting though the various methods of carb tuning. Small or large tapered needle, small or large transition areas and which point on the needle to place that, length of needles, should the rear needle be slightly shorter or longer. Should jets be a straight cut hole or tapered for flow rate. Does one block an air bleed or make them bigger and then do you use smaller or larger mains. Should emulsion tubes be swapped over or be the same (made leaner or richer). Then there's the diaphragms, how many holes and what size should they be, short or long spring, angle on the slide transition area. Should the rear carb be run cooler (richer) or not. Should one mix or match components etc etc. :lol:

I suspect there is even a difference between the Keihin needle tapers in the States compared to here as they have different part numbers, so catering for various climatic changes. You can buy different needle profiles from Keihin for richer or leaner!

It's a Black art with a lot of trial and error. I might get one of those cheapie sigma kits as they are cheap and the curiosity in me is biting. Might be worth it just for the needles.

This is another reason why I want to get a carb dissected down the middle. I want to see inside and which route the passages take and how they possibly integrate with each other. Pilot for example we know this tapers off towards the mains, but how? they sit right next to each other in the float bowl. Then there's how the fuel screw interacts with the pilot. Or the main air bleed leading down to the main jet, does this taper off? How does the needle and main jet interact or main air bleed as it may be with each other where it enters the carb throat.

(:-})
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tony.mon
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Re: Carb Needles

Post by tony.mon »

cybercarl wrote: art with a lot of trial and error. I might get one of those cheapie sigma kits as they are cheap and the curiosity in me is biting. Might be worth it just for the needles.

This is another reason why I want to get a carb dissected down the middle. I want to see inside and which route the passages take and how they possibly integrate with each other. Pilot for example we know this tapers off towards the mains, but how? they sit right next to each other in the float bowl. Then there's how the fuel screw interacts with the pilot. Or the main air bleed leading down to the main jet, does this taper off? How does the needle and main jet interact or main air bleed as it may be with each other where it enters the carb throat.

(:-})
I'm bringing one to the ws day for you
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