BS34 Adjustable Needle Question

[MFJustin]

Picked up an '81 motor to use in my current build. It came with the BS34's, pulled all of the jets and it seemed like the PO had gone up quite a few sizes in everything. Carbs needed a pretty thorough cleaning but I've got everything mostly finished up save for redoing the jet sizes.

My plan was to take everything back to stock, 132.5 main jet size and a 42.5 pilot. The set up is going to be a PMA/Pamco, UNI Foam Filters and the stock exhaust cut down before the muffler so essentially straight pipes. I know that I will probably have to tune it more when its all said and done but I wanted to take everything back to stock sizes and work from there. As it stands right now I have all of the stock jet sizes ready to go in, the one tip I took into consideration after reading around here was to swap out the fixed clip needle with an adjustable one. I picked up this needle from Mikes XS which I'm hoping was the correct one. http://www.mikesxs.net/product/48-0663.html

My questions in regard to this easy swap are:

1.) If I am taking all of the jets back to stock sizes for a baseline to start the tune on, what position on the needle should I place the clip that would be "stock". I'm assuming that once I get everything buttoned up and start to fine tune it, I can just follow the guidelines for BS38 needle adjustment?

2.) Does the rubber donut with alignment hole from the stock needle need to be swapped over to the new adjustable needle? I am going to assume that it does need to swap over but I wanted to check first.

Included are pics for reference. Thanks in advance guys!!!

 

[nanoonanook]

Canadian model (with adjustable needle clips) are stock in the 3rd position, or the middle clip position. Apparently, this will be fine for pods and open exhaust if you have the proper jet sizes and idle screw is set properly.
As I understand it (I'm new at this myself, but have read a lot....... for what its worth) each bike is different and additional tuning is needed, unless you get lucky.
Good luck,
A

 

[MFJustin]

Thanks for the response. I kind of did a guesstimate based on patchwork information I've come across and figured it needed to go in the third (middle) slot. Just wanted to get the carbs back to stock form and then tune accordingly based on the mods and how the bike runs.

Still curious about the little rubber donut. I think it would make sense to get swapped over to the new adjustable needle. The question though would be does it get snugged completely up against the adjuster clip or what?

 

[5twins]

That needle used with stock components may not work so well. It's supposed to be run with the Canadian needle jet, which Mike's also sells. The 2 parts are a matched set.

 

[nanoonanook]

Sorry, I missed that part. Yes, the donut is used as well.... oops, looks like 5twins beat me to the punch!

 

[MFJustin]

5twins I actually was unaware of that so thanks for the heads up. Let me ask you this though, with the mods I had listed is it possible to get away without having to use an adjustable needle, just retain the stock one and tune the rest of the jets accordingly or is it a must have?

*Nevermind unless I am incorrect after more reading of the carb guide the needle adjustment is necessary for mid range tuning. Looks like I need to order that needle jet now.

 

[weekendrider]

Or you could use the stock needle and shim it with washers?

 

[5twins]

You may or may not need the adjustable needle. I've tuned several sets of BS34s for bikes with various mods and didn't need the adjustable needle. On the stock BS34s, the midrange is set up very lean from the factory. When you increase mains and pilots for mods, they bleed over into the midrange and make it richer too. In many cases, this just makes the midrange right so no needle adjusting is needed. Usually, once you go more than a couple sizes up on mains, the bleed-over from them makes the midrange too rich and needle tuning (leaning) is needed. As I said, sometimes with the BS34s, that added fuel from larger jets just makes the midrange right. You will have to try it to be sure but personally, I wouldn't get the adjustable needle unless you found it was needed.

The BS34 needles are spring loaded from the top in the slide. That means you can only shim them up (richer). Adding shims above the clip, which is what you would do to try to lean (lower) the needle, does nothing to alter needle height, only preloads that little spring more. With larger jets making the midrange too rich, you want to lean the needle and that's just not possible with shims in the BS34s. The only way you could do it would be to file that thick plastic spacer with the locating nub thinner. If it came to needing to do that, then I would spring for the adjustable needles instead.