Carburetor Needle Identification marking - 34mm/81 special

[Peejay]

Hi all,
I just got to repairing my carbs and replaced most stuff OK until I came to the needle.
The one coming out carried the Identification 5HX12. The new one out of the packet was marked 5Ix11.
The original is worn so I don't want to go back but I can't find any discussion on what the markings may mean.
Equally I don't want to install the carbs if the needles are way out
Visually the tapers seem about the same form using a micrometer but having worked with SU carbs I know that can be misleading, taper rates can affect performance at different openings quite dramatically.
I got the rebuild packs from Heiden and they look the genuine article, made in Japan etc
Has anyone got a chart of needle identifications/dimensions that can help or give any advice on what the difference may be?
Thanks
PJ

 

[5twins]

The 5HX12 is the stock needle for most of the BS34s. It has only one clip slot so you can't adjust its setting. The 5IX11 is what's known as the "Canadian" needle. It has 5 clip slots so can be adjusted but I think the taper is very similar, if not the same, to the stock needle. It is richer than the 5HX12 because it's shorter. It's supposed to be a performance upgrade for the BS34s because they came set up very lean from the factory.

As far as where to set it, you will probably just need to experiment. The stock 5HX12 measures 50mm from the clip down to the tip. The "Canadian" 5IX11 measures 50mm from the clip to the tip with the clip in the top slot. That means running it in the middle slot would be 2 steps richer than the original.

MikesXS also sells a matching Canadian needle jet and recommends the two components be run as a set. I see Heiden doesn't offer that jet. I don't know how the Canadian needle is going to work with the original needle jet. Like I said, you'll just need to experiment with settings.