Finding my standard...

What you have to realize and take into account when tuning carbs is that the three circuits in there overlap slightly. Changing one influences the one or ones next to it as well. In the case of the needle (midrange), a change will affect the lower part of the main as well as the upper part of the idle circuit .....

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ok, pulled the other bowl and stamped sizes are the same. The left carb jets look newer and in better shape.
Comparison pics.. Blue / Left Carb - Red / Right Carb
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Sounds like I should just start fresh and order a handful of brand new pilots and mains. Any suggestion on a good place to source them? I see Niche Cycle Supply offers them at around $4 each :umm:
 
No pics in your post.
Niche is my go to for jets.
I can't help on the mains, but I've got 2 almost new #45 pilots. Yours for the cost of a stamp? PM me if you want 'em.

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Yes, Niche Cycle is a good place. Make sure you get the genuine Mikuni jets because I think they sell knock-offs as well. I usually buy them in 4 packs because I'm always doing some carb fooling, but in your case that won't work out. Your '75 and '78 models use different sizes and different types of pilots.

As you'll discover, Mikuni makes quite a few different styles of main jet. Your BS38s use the N102/221 type, nicknamed a "small round" main .....

M98LIeO.png


http://www.nichecycle.com/ncs/categ...ets/n102-221-n102-221-main-jet-by-mikuni.html
 
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Here's a brand new 125 and 145 compared side to side. It's pretty easy to see the size difference with the naked eye .....

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And this shot, even though it's a bit blurry, nicely illustrates the smooth sides of the orifice hole .....

RJgI3OR.jpg


It is still hard to determine whether your 125 is enlarged or differently sized. But, if it hasn't been altered, it's the wrong size anyway. Stock size is a 127.5, and with your freer flowing exhaust that may not even be big enough.
 
The website where I found this chart states mikuni jets are rated by flow testing and not hole size so all Mikuni sizes are "approximate"
Keihin, Dynojet, Mikuni Jet Size Cross Reference
All Hole Diameters Are in Inches
Hole Dia”---Keihin # -- DynoJet # -- Mikuni #
0.0350---- 92.5--------- 92----------- 86.3
0.0360---- 95----------- 94----------- 88.1
0.0370---- 97.5--------- 96----------- 90
0.0380---- 100---------- 98----------- 91.9
0.0390---- 102.5------- 100---------- 93.8
0.0400---- 105--------- 102---------- 95.6
0.0410---- 107.5------- 104---------- 97.5
0.0420---- 110--------- 106---------- 99.4
0.0430---- 112.5------- 108--------- 101.3
0.0440---- 115--------- 110--------- 103.1
0.0450---- 117.5------- 112--------- 105
0.0460---- 120--------- 114--------- 106.9
0.0470---- 122.5------- 116--------- 108.8
0.0480---- 125--------- 118--------- 110.6
0.0490---- 127.5------- 120--------- 112.5
0.0500---- 130--------- 122--------- 114.4
0.0510---- 132.5------- 124--------- 116.3
0.0520---- 135--------- 126--------- 118.1
0.0530---- 137.5------- 128--------- 120
0.0540---- 140--------- 130--------- 121.9
0.0550---- 142.5------- 132--------- 123.8
0.0560---- 145--------- 134--------- 125.6
0.0570---- 147.5------- 136--------- 127.5
0.0580---- 150--------- 138--------- 129.4
0.0590---- 152.5------- 140--------- 131.3
0.0600---- 155--------- 142--------- 133.1
0.0610---- 157.5------- 144--------- 135
0.0620---- 160--------- 146--------- 136.9
0.0630---- 162.5------- 148--------- 138.8
0.0640---- 165--------- 150--------- 140.6
0.0650---- 167.5------- 152--------- 142.5
0.0660---- 170--------- 154--------- 144.4
0.0670---- 172.5------- 156--------- 146.3
0.0680---- 175--------- 158--------- 148.1
0.0690---- 177.5------- 160--------- 150
0.0700---- 180--------- 162--------- 151.9
0.0710---- 182.5------- 164--------- 153.8
0.0720---- 185--------- 166--------- 155.6
0.0730---- 187.5------- 168--------- 1575
0.0740---- 190--------- 170--------- 159.4
0.0750---- 192.5------- 172--------- 161.3
0.0760---- 195--------- 174--------- 163.1
0.0770---- 197.5------- 176--------- 165
0.0780---- 200--------- 178--------- 166.9
0.0790---- 202.5------- 180--------- 168.8
0.0800---- 205--------- 182--------- 170.6
0.0810---- 207.5------- 184--------- 172.5
0.0820---- 210--------- 186--------- 174.4
0.0830---- 212.5------- 188--------- 176.3
0.0840---- 215--------- 190--------- 178.1
0.0850---- 217.5------- 192--------- 180
0.0860---- 220--------- 194--------- 181.9
0.0870---- 222.5------- 196--------- 183.7
0.0880---- 225--------- 198--------- 185.6
0.0890---- 227.5------- 200--------- 187.5
 
Thank you Gary. I've seen a similar or maybe even that chart on a 2manyXS1B's thread as well. I just am confused still about the 2 sets of #135's I've reamed up to .058+" over the original measured diameter of .055
:umm:
 

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Yes, I could never see the point to drilling jets out. They are a precision part and not very expensive. Just buy the size you need, and buy genuine ones.
 
Most likely I will need some 137.5's again. I do have an advantage to address precision parts features as I do infact make even more precise parts than carburetor jets for a living everyday. I am able to greatly magnify and inspect items such as jets at work with modern inspection views. If those bores are tapered, it was a mistake on my part somehow to notice that? Regardless, I do expect to continue the tuning needs for sure in the future. Everybody should know my local parts sourcing habits which have been hugely affected in the Pacific Northwest by the Covid shutdown.
One more mention is all the fraud occurring with online purchasing. In the past 3 months I have had my credit card used fraudulently twice and then canceled. My PayPal was used last week in Texas in attempt to purchase a few flashlights lol.. I have canceled my PayPal, Ebay etc. Have gone as simple online as possible out of frustration. This site is the only online membership I even remain on.
On the upside, I continue to have very nice experiences with XS.com members in regards to parts sharing :)
I have many times sent XS parts all over the US and even Canada and have Never been disappointed by a fellow motorcyclist!
Long live our honesty and helpfulness to each other with XS parts and camaraderie.
Hope to test this carb set soon.
-R
 

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New jets arrived today. A big thanks to Jim for the #45’s he sent me in the mail. Also ordered some 130 and 132.5 mains from Niche Cycle for about $4each. I’ve been doing a lot of thread reading on jetting lately hoping to gain a better understanding of what the hell I’m trying to do. First off I decided to take some pictures to document and I go so I can refer back if needed. As stated, carbs are very clean. Previously vapor blasted by OkdSkoolCarbs.
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New jets going in. 45 pilot, 130 mains. Needle clip is in slot 4 which is factory setting. New diaphragms replaced last winter too. I checked my needle jet and it was a little loose. I was able to remove it with a light wiggle. While it looks clean, I cannot get it to seat back in securely. How tight does this need to be? Is there a trick to getting some stiction in there? Do I need to worry about replacing the o-ring?
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Fortunately I do have spare carb parts if needed. Including needles and needle jets, as I understand there are no replacement needle jets offered for 74/75 bs38’s.
 
The float bowl lip clamps it in place. a new oring will make that a tight hold. or I spose a BIT of loctite wouldn't hurt anything.
 
Today I got a new set of grips in the mail. I specifically chose these Biltwell KungFu grips because I needs to cut the ends out to mount my new bar end mirrors and these grips looked to fit the bill for me. I’m pretty disappointed though as I figured out after I cut and mounted the left grip and mirror that they sent me two left grips. There is no way the right grip will fit over the throttle sleeve. I ordered these through Revzilla, but I’m unsure how they will respond to my email complaint since I already cut the left grip end. WTF?
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Today I got a new set of grips in the mail. I specifically chose these Biltwell KungFu grips because I needs to cut the ends out to mount my new bar end mirrors and these grips looked to fit the bill for me. I’m pretty disappointed though as I figured out after I cut and mounted the left grip and mirror that they sent me two left grips. There is no way the right grip will fit over the throttle sleeve. I ordered these through Revzilla, but I’m unsure how they will respond to my email complaint since I already cut the left grip end. WTF?
View attachment 177398 View attachment 177399 View attachment 177400 View attachment 177401

Well shoot, that’s a shame, and a hassle.
 
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