Author Topic: Mikuni needle jet bore sizes, 159 type  (Read 893 times)

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Offline John Orchard

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Mikuni needle jet bore sizes, 159 type
« on: April 16, 2023, 07:05:46 PM »
I'll post this here, it took me long enough to find it, sure there is someone out there that has a more complete listing. These are for the 159 type needle jet for Mikuni VM30, 32 & 34, not sure if the sizing correlates to other models.

Description codes & bore sizes.

O-4 = 2.620mm
O-6 = 2.630
O-8 = 2.640
P-0 = 2.650
P-2 = 2.660
P-4 = 2.670
P-5 = 2.675 (half size)
P-6 = 2.680
P-8 = 2.690
Q-0 = 2.700
Q-2 = 2.710
Q-4 = 2.720
Q-5 = 2.725 (half size)
Q-8 = 2.740
R-5 = 2.775 (half size)

I thought I'd have a play drilling out some needle jets but I don't own any equipment exact enough :-) I guess I just wanted to know if the bore size was the only specification that changed with the description code. In a pinch, if I needed a richer 1/4 throttle (the point where the needle jet bore size and needle straight section are in play) I'd consider reaming out the needle jet ID with some tapered jet reamers I have. Being the butcher that I am ;-)
« Last Edit: April 17, 2023, 11:42:13 AM by John Orchard »
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Offline PeterC

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Re: Mikuni needle jet bore sizes, 159 type
« Reply #1 on: April 16, 2023, 07:30:50 PM »
Thanks for that John. Sometimes getting hold of the correct information is worse than pulling teeth. The sizes mean more than model nos
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Offline Tomas

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Re: Mikuni needle jet bore sizes, 159 type
« Reply #2 on: April 18, 2023, 04:14:56 AM »
Hello
This web site also has a needle jet chart.
https://www.thumpertalk.com/forums/topic/1224849-mikuni-tmx-needle-decoding/
Need to scroll down about half way. I got a good result drilling out not sure what size needle jet to size S-0 just by using a 2.8mm drill bit  :D

Offline John Orchard

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Re: Mikuni needle jet bore sizes, 159 type
« Reply #3 on: April 18, 2023, 08:31:48 AM »
Hello
This web site also has a needle jet chart.
https://www.thumpertalk.com/forums/topic/1224849-mikuni-tmx-needle-decoding/
Need to scroll down about half way. I got a good result drilling out not sure what size needle jet to size S-0 just by using a 2.8mm drill bit  :D


Interesting, thanks. Looks like the sizing code is used across multiple jet styles.
Johnny O - Tahition_Red factory rider.

Offline Momus

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Re: Mikuni needle jet bore sizes, 159 type
« Reply #4 on: April 18, 2023, 12:12:59 PM »
Hello
This web site also has a needle jet chart.
https://www.thumpertalk.com/forums/topic/1224849-mikuni-tmx-needle-decoding/
Need to scroll down about half way. I got a good result drilling out not sure what size needle jet to size S-0 just by using a 2.8mm drill bit  :D

Ditto for similar job.
Used a drill a size under then finished to size.
If you love it, lube it.