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Post by stevec5000 on Apr 7, 2008 20:38:20 GMT -5
Does anyone know off hand why the main jet is called 300? If it is measured the same way as other Yamaha jets, that is to check the diameter of the hole, it would be a #150 since the hole is 1.5mm diameter. In fact I have some other jets the same size out of an XS750 that are actually marked 150 so why did they call this one 300? Anybody know what it means?
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Post by colinjay on Apr 7, 2008 23:01:59 GMT -5
Jet sizing is done in three ways. One way is by the diameter of the jet oriffice, another by the cross sectional area of the jet orifice and the more common way is by the actual flow rate of the jet oriffice in Cubic Centimeters (cc/ml) per minute. Mikuni Hex jets are sized by flow rate, so if the jet is a #300 mikuni hex jet it will flow 300 cc/ml per minute. There is a chart on Iam Williams web site, www.iwt.com.au/MIKUNI.HTM which shows how the sizings for the mikuni hex jets progreess. CJ |
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Post by aero on Apr 8, 2008 10:38:48 GMT -5
I have a list of the drill sizes that approximate the mikuni jet sizes. If you want it PM me, I'll have to scan it is as its an actual 'real' documant at the moment.
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Post by miker on Apr 9, 2008 10:22:18 GMT -5
<<Jet sizing is done three ways>>
Sometimes I think the world would be better run by squirrels. Henceforth I'm going to start asking for metric bolts by their cross-sectional area.
miker
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Post by colinjay on Apr 13, 2008 19:44:56 GMT -5
Miker,
You might as well give it a try.
One of my pet hates when I worked as a bike mechanic back in the early '80's (and still it is actually) was people who asked for bolts by the size of the spanner that fitted the bolt head, i.e. " Can I have a 50mm long, 10mm bolt"?, but they really wanted a 50mm long 6mm bolt, and then got pissed off when you gave them a 50mm long 10mm bolt?
CJ
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Post by spindlehead on May 4, 2008 13:45:57 GMT -5
To confuse things, Mikuni calibrates some jets backwords from the direction they function in the carburetor. Those jets flow less in the "forward" direction. The typical VM (round slide) main jets with the hex head are calibrated backwards. Some mikuni jets like the button or slot type found in your flat slide carburetors are designed to have the same flow in both directions. A#320 hex head jet flows the same as a #160 button head. Thats why jetting numbers always look so differnt between the round and flat slide carbs. The document below is awesome and explains all. Read it 3 times as the author suggests: "MIKUNI MAIN JETS EXPLAINED or HOW I SAVED BIG BUCKS JUST BY LEARNING THIS STUFF" www.ozebook.com/compendium/t500_files/mikuni.pdf |
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Post by stevec5000 on May 4, 2008 18:29:26 GMT -5
That's why I only go by the hole diameter and ignore the other nonsense. Besides that's all I can measure.
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Post by aero on May 5, 2008 4:15:52 GMT -5
hey spindlehead, top post! I've often looked at the amal type jets and thought that would flow better in in the opposite direction. I never actually clicked that that is exactly the reason why the slotted and the hex jets vary! You never stop learning stuff!
That too would also explain why drilling jets only works reliably once or twice and then for relatively small increases
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Post by caferacercarl on May 8, 2008 3:31:08 GMT -5
Colin, you still know more than most every bike shop, good work ,its all about drill bit size and thats whats fun about swapping carb makes between bikes, one day I will photo all my jets and drills on the floor, it will blow you away,a bag full of drills just between 1 to 2mm! curly has seen it all when we did his bike. stevec5000 does what I do..
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sven
Full Member
Posts: 166
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Post by sven on May 11, 2008 6:17:58 GMT -5
That's why I only go by the hole diameter and ignore the other nonsense. Besides that's all I can measure. Gauge.  |
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