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Re: Motorcycle main jet sizes

To: Bryan Savage <b.a.savage@earthlink.net>
Subject: Re: Motorcycle main jet sizes
From: "todd" <todd@twinjugs.com>
Date: Mon, 26 Jul 2004 02:05:01 +0000
Good point Brian, not sure about cars but when it comes to the japanese 
harley carbs there are so many companies making jets for the same carb and 
they are all punching them out so fast that the internal constant diameter 
length is seldom an exact constant from just one manufacturer, let alone 
between all of them. I'll bet some of you could get into working or polishing 
the jets and hourglassing or funneling them and on and on(wouldn't mind 
hearing about it to tell ya the truth, i don't know much about it besides 
keeping it uniform). 
Persoanlly I think what the jet size actually measures(smallest inside 
diameter through the jet)should be the stated as standard and anything else 
done(other then a hand drilled straight thru hole, which I like) should be 
done to all the jets ever used in that carb so a #70 is a #70 and a #75 is a 
#75, not that a #70 flows like a #75 but instead that it flows like an 
excellent #70. In other words.. if you have a #70 that flows like a #75... 
you either have a shitty #75 jet and should make it flow better, or you put 
to much work into the #70 jet. I would think it would be much easier to put a 
#75 in for the average guy(myself included)as long is it's built exactly like 
the other ones your dialing it in with.. i always use the same set of bits, 
handspin them and match port lengths of the jets for this reason. I think he 
just wanted to know if there was an industry standard to the markings though -
 lol. But what do i know, I had to look up propitious to find out it meant 
advantage. :-)
TD


> I don't know if Holley still does it, but they used to flow test 
> their performance jets and THEN mark them. The hydrodynamic 
> propitious of the entrance, exit, surface finish, diameter and 
> length of the orifice are all have an effect on the flow. I can make 
> a # 70 Holly jet flow like a # 75 and a drill can't detect it 
> because I won't change the diameter of the hole,
> 
> Bryan






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