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Discussion Starter · #1 ·
Drill size to drill out Keihin jets to #70 and #72

What is the drill sizes to open up a Keihin jet to Keihin sizes #70 and #72?

Thanks
 

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From what I understand. 70 = .70 and 72 = .72
 

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Sensei
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Well, you will want number drills, but METRIC ones..... a 70 jet is .70mm....You could convert to english measurements and use the appropriate number drill.... Somehow, I'm not believing a #70 drill is exactly 70 anything....(.70mm or .70") :eek: .....
 

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66Sprint said:
Well, you will want number drills, but METRIC ones..... a 70 jet is .70mm....You could convert to english measurements and use the appropriate number drill.... Somehow, I'm not believing a #70 drill is exactly 70 anything....(.70mm or .70") :eek: .....
Number sizes came from the old wire size, when making wire they would force the hot wire through a die, and yes, the first die size was (in the US) #0000 (not quite 1/2inch) so to get finer wire they needed to use ever decreasing sizes all the way down to #80 die. As the technology advanced they were able to use larger die's as a starting point, so the letter sizes came about starting from A, and working up to Z the largest. 0, 00, 000, 0000, A, B, C, D etc

Now to completely screw things up, there is at least 4 different wire gauges based on different principles and maths and of course the French have their own. But for you 'Mericans the one above is yours ;)

I have worked on Aircraft all around the globe and once work in a hanger restoring vintage military aircraft, that had a Mitsubishi (JIS metric) Cessna (US Imperial) Spitfire (Imperial, Whitworth) and Dassault Mirage (french, Metric) which gave us a HUGE selection of tool and problems!

The British wire gauge (or SWG) is still used by some manufactures to give the thickness of sheet and of all things guitar strings.

Along came the Imperial and Metric systems and the number size system died out, well sort of.

Back to the topic
... strangely :? #70 is 0.0280 of an inch or if my maths are right 0.07112mm, but sadly still not the right size.

Japanese bikes, think metric for everything :D Don't get me started on JIS v DIN v ISO :x OR bolts :cry:
 

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So yes a #70 drill would be a 71 Jet
 

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Discussion Starter · #7 ·
:shock: :? :) :roll: :| :oops: :cry:

I'm so confusid!!!!
How do you know that the drill bit you buy matches the #70 is a #71 orifice?

If I use my simi trustworthy vernier gauge, on the drill bit I need to drill out a #70 or #72 hole,
what would the mm reading be???
 

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Greenbush said:
:shock: :? :) :roll: :| :oops: :cry:

I'm so confusid!!!!
How do you know that the drill bit you buy matches the #70 is a #71 orifice?

If I use my simi trustworthy vernier gauge, on the drill bit I need to drill out a #70 or #72 hole,
what would the mm reading be???
When you get down to that size a "vernier guage" is not going to cut it. You really need to be using a Micrometer.
 

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Discussion Starter · #9 ·
MNellis said:
Greenbush said:
:shock: :? :) :roll: :| :oops: :cry:

I'm so confusid!!!!
How do you know that the drill bit you buy matches the #70 is a #71 orifice?

If I use my simi trustworthy vernier gauge, on the drill bit I need to drill out a #70 or #72 hole,
what would the mm reading be???
When you get down to that size a "vernier guage" is not going to cut it. You really need to be using a Micrometer.

Right. A bit hungover today. I just so happen to have a antique micrometer. I think it's a SAE one. What
would the reading be for both SAE and Metric, incase?
 

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Sensei
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Metric would be .70 and .72mm.... Just convert to get the "english measurement....Conversion tables/calculators available online ...free..... :D
 

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As Steve said, forget Imperial and number # sizes, just use metric..... 0.71mm or 0.72mm :roll:
 

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I've always heard that drilling jets was a no-no - you can get the right size, but then the shape is screwed up.
 

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What shape?...A round hole?... The jet is just a sized orifice to control flow rate.....
Admittedly, you could drill at an angle (crooked) and screw it up..... I've soldered large jets shut and redrilled (smaller) many times........Simply opening them up is easy....
 

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Clay, my buddy Edgar that you met today thinks he might have the drill bits needed to open up your jets for you.
He will have them here next week or can have them here tomorrow.
He has this set of micro drill bits that are awesome, I use them when I have to rebuild a non rebuildable Honda petcock.
 

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66Sprint said:
What shape?...A round hole?... The jet is just a sized orifice to control flow rate.....
Admittedly, you could drill at an angle (crooked) and screw it up..... I've soldered large jets shut and redrilled (smaller) many times........Simply opening them up is easy....
Yes, I've heard of drilling jets but also have heard that you shouldn't - the excuse is that the tapered inlet and outlet of the jet is a specific shape as well and will be damaged by drilling.
 

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Old wives tale..... as long as you have a decent chamfer and a smooth (clean/sharp) transition there will not be a problem.... Admittedly, a hand drill is not the way to go, but a good drill press and/or a lathe is a different story.... ;)
 

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Makes perfect sense to me....
 
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