Author Topic: Carb jet# sizing cross referencing to inch sizes.  (Read 2983 times)

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Offline byidesign

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Carb jet# sizing cross referencing to inch sizes.
« on: February 27, 2006, 08:31:30 AM »
Does a chart exist, that crosses jet sizing .size#, to the exact. thousandth of an inch diameter
  that the jet actually is for example,  {ie. # 35 = .016  etc} I have some cb750k 1978 carbs ,that the
    slo jets , are too far gone{press type} and I would like to make replacements for them.
    { no two carbs are alike using pin guages. } and don't want to guess at it.
         Thanks
                 Bruce
82CB650SC,80CM400

Offline TwoTired

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Re: Carb jet# sizing cross referencing to inch sizes.
« Reply #1 on: February 27, 2006, 11:05:44 AM »
The jet numbers are in metric units, with #100 being 1.00 mm.   A #35 would 0.35 mm.  Converting from metric to inch is fairly straightforward. See:
http://www.onlineconversion.com/
For example.

0.35 millimeter = 0.013 779 528 inch

If you are going to use a common twist drill to enlarge openings, note these make larger holes than their shank size as they wobble in the hole they make.  Jet reamers make a smoother flowing hole.  You can find jet guages where you find jet reamers.

Best option is get replacement jets in the size you desire.

Cheers,
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC

Popeye: "Wrong is wrong, even when it helps ya."

Offline byidesign

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Re: Carb jet# sizing cross referencing to inch sizes.
« Reply #2 on: February 28, 2006, 04:36:41 AM »
 I was not sure that the numbers were straight  to metric. as some companies,
  use their own systems. I have been unable to find the {press in} type slo jets for
    the pre CV type carbs, so I wanted to make some new ones.
       with a small amount of heat, the old ones slid right out of the castings.
           Thanks..
82CB650SC,80CM400

Offline n9viw

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  • Floyd, '76 CB550k
Re: Carb jet# sizing cross referencing to inch sizes.
« Reply #3 on: February 28, 2006, 09:20:42 AM »
There is a bit of correlation- a #40 jet is 0.040mm, a 105 jet is 0.105mm, etc. You can convert from jet to wire drill sizes by following the chart that's halfway down this page: http://en.wikipedia.org/wiki/Drill_bit_sizes .
Bear in mind, factory jets are STEPPED- without that venturi, you don't get the slight acceleration of fuel and potential atomization that you do from a factory jet. One way around this is to drill the jet to the size you need, then drill ALMOST to the middle from either end using a bit two sizes larger than the first one you did. That should leave a slight venturi in the middle of the jet, which will still approximate the factory milling. If you screw it up, you can always solder it closed and do it again.
Nick

'76 Honda CB550k
'73 Honda CB750k

Offline TwoTired

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Re: Carb jet# sizing cross referencing to inch sizes.
« Reply #4 on: February 28, 2006, 10:49:56 AM »
I was not sure that the numbers were straight  to metric. as some companies,
  use their own systems.

If they use their own system, then they should also have a conversion chart.

I have been unable to find the {press in} type slo jets for
    the pre CV type carbs, so I wanted to make some new ones.
       with a small amount of heat, the old ones slid right out of the castings.
     

You don't need the heat to pull out the slow jets just a firm yank.   And, you can use screw in type in it's place with the proper loctite.  Cvillechopper and Buffo did this with their carbs.

Cheers,

P.S.  n9viw is the victim of a misplaced decimal.

Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC

Popeye: "Wrong is wrong, even when it helps ya."

Offline n9viw

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  • Floyd, '76 CB550k
Re: Carb jet# sizing cross referencing to inch sizes.
« Reply #5 on: February 28, 2006, 11:37:14 AM »
By God, so I am!  ;D 105 jet would be 1.05mm, not 0.105. Silly me, didn't read so good.  ::) Thanks for catching that, TT.
Nick

'76 Honda CB550k
'73 Honda CB750k

Offline byidesign

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Re: Carb jet# sizing cross referencing to inch sizes.
« Reply #6 on: February 28, 2006, 11:43:36 AM »
Thanks for the info, i know what my weekend project is now !
        Bruce
       
82CB650SC,80CM400

 

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