Bonneville America Forums Forums Technical Forums Performance Mods To much infomation running around my head!?!?!?

To begin, many thanks to the creator of this web site. Its a good thing. I hope my contribution helps in your efforts.

Now the reason or this post, I need help in determining the best starting point for my carb's jets.

The 2004 790cc Speedmaster I own has the Triumph Speedmaster off road exhaust, 18 tooth sprocket, and an Uni filter installed. I, also, have removed the AI and the snorkel.

While exhaust was being install, I ask shop manager at Kingsport Cycles to increase the jets to the next size. After paying for 2 jets and the assoiated labor, the bike seemed to run lean, ie it ran better once the bike warmed up.

A year later, I researched the problem and found the Jenks bolt web site. I exchanged emails with the owner, and ordered the reconmened set of 45 idle and 130 main jets. I decided to wait for cool weather to set in before installing the jet kit. In the meantime, I found about the advantage of the Thruxton needle, so an order was placed for a set.

With the needles on the way, I began the disassembly of the carbs. You can imagine my disappointment when I found the orignal jets still install, and the end an electrical lug connector under the needles. I should have asked for the old parts as proof of the work done. I am now older and wiser.

I digress. Back to the subject of the post. I have researched web sites, downloaded the .pdf on the Jenks web site ( Click Here ), used the BonnevilleAmerica.com jetting giude, read all the forum post that could be found, and googled it seven ways to Sunday. Now I suffer from information overload, and am not sure where to start.

I do not know of a dyno located in mountains Northeast Tennessee. So, I going use the throttle response and sparkplug color to tune the jet size. My research makes me feel the the 45/130 combination, when used Thruxton needle, maybe to rich. If this is the case, could someone please recommend a better jet combination? I realize there maybe other considrations, and what worked for someone else may not work for me. I am just try to save a little time and effort by finding a good starting point.

Thanks in advance for the advice. I just wish I had a honest local dealer I could turn to, but I am sure I found the right place in leu of that.

I have an 05' speedy which is a bit different. But jetting should be very similar. I also have a UNI filter and snorkel removed, but i also have the bottom of the airbox/filter drilled which basically doubles the intake area into the filter. Running stock pilots with 130 mains and thruxton needles. However, i changed the needles back to the TBS needles i had in it before the thruxton. The main difference between the thrux and TBS is length. But i ran the thrux with no shims and the TBS with enough shims to made them the same length as the thrux. That makes them almost exactly the same because the taper is so close it's hard to tell if theres a diff with the naked eye. Going back to the TBS has shown me that the thruxtons with no shims and TBS shimmed to get the same length are almost the same as far as performance, tho the thruxtons seemed a tiny bit rich by comparrison as far as i can tell.

Anyway, i think for you they might be too rich due to the fact my airway is opened up more than yours and mine is on the edge of over rich i believe. Then again i know of another member who has a 04' with the same setup as you, IE: no snork, UNI, and NO hole drilled like me. he's running thruxtons and i think 130's also and say his bike is running very good. So i would say that the difference between the 05' 865 speedy and earlier 790's may be responsible for the difference and you should find that setup will be great. If not i would think dropping the mains down to 125 would take care of any problems which might occur when at throttle settings where the needles and mains are both in action equally such as near full throttle.

So i would go with just what you mentioned and see where you stand in the mids and top. If it runs great but feels like it's bogging down somwhat at near to full throttle, drop the mains to 125. If the mids aren't strong go back to the stock needles and shim them one shim at a time till it's good. i think you be ok tho.

The current needles have the code NBAD stamped on them. Is that the same as the TBS needle?
Jenks has a set up for needles coded NBTZ and NBZY. Is the NBTZ code the same as the TBS needle?

Jimmy,
I have a 2004 Speedmaster also.
I have Tpipes.
I had the bike dynoed with the snorkel removed & stock jetting<120 mains>.
The bike pulled 64.1.
I then had it dynoed again with 125 mains & thruxton needles.
The bike then pulled 67.8.
NBAD are the stock needles.

Jimmy,

TBS needles are N3RF and the Thruxton needles are NBZT. TBS needles are Triumph part #T1241024. However, I am going to suggest you takes things slowly and not go and change everything at the same time. If you do and something is screwed up, it's going to take you longer to dial it back in.

What kind of riding do you do? Around town or lots of back roads? Do you regularly get up to the top of the revs or stay around 3-5K? How did you determine it was running lean? Seat of the pants? Plugs?

I am going to assume you ride the twisties a lot, typically keep the RPMs up, and used the plug/seat dyno to determine lean....

I would leave the idle circuit alone right now. I would also not touch the needles yet UNLESS you are experiencing a midrange RPM slump (or dip in power). There is nothing wrong with the stock needles in a more or less stock bike. If anything, you could shim the stocker with one or two shims. I would concentrate on the main circuit. As long as you have 130s on the way, use them. Swap them out and take her out for a ride and see what's up. Go up or down from there (I'm betting closer to 125 might work). Once you have the mains close, you can try shimming the stock needles.

Main thing is, try things one at a time and go slowly.


Work

This is great. I am impressed with the quick and thought responses. Thanks.

Anywho, I mostly spend my time on riding highways. I, however, find myself dragging the footpegs at times. (I need more ride height, but thats a post for another day.) I have a set of saddle bags and a sissybar with the rack on the way, and am planning on some site seeing next season. The mountain roads around here make life grand for a Triumph rider.

I have not check the plugs in while, but the last I did check, shortly after the exhaust install, the had a light brown hue.

I suspect the lean condition because, even with the choke applied, it takes a couple of cranks to get it going. Once running, it will not take take any throttle without missing a time or two. After a long few minutes of idling, it seems right as rain. Also, the top end is a bit weak. Am I correct in assuming a lean condition? (We all know what happens when one assumes.)

Mine also needs a couple of cranks before going (choked). I warm her up for about a minute and then proceed, still on chole. After a few minutes, I can push the choke but there are occasions where she needs more time to warm up. I have no problem with this because once warm, she runs great.

Light brown is OK but if you are missing the top end, a larger main would probably help (richer).

Hmmm. I am basing my assumptions on my previous rides (water cooled Kawasakis). They did no require as much warm up time. Is that an air cooled thing?

Anywho, I removed one off my plugs. It looks good, at least accord to this spark plug color chart. It was close in appearance to image number 20.



This setup for this plug;

• 120 Main Jet
• 42 Idle Jet
• An Electrical Lug Connector Under Each Needle
• Uni Filter
• Triumph Speedmaster Offroad Exhaust
• No Snorkle
• No AI

So, I have decided to make the starting point the stock jets and the Thruxton needle. If anyone interested, I'll blog trails and errors at the post.

Winter is just setting in here, so I'll have to wait for breaks in the weather for road test of changes my. It does not get to bad around here, and maybe I'll be able to get a few good runs in before spring.

I Wonder how should I allow for the effects of cold air. Will cool dense air make it appear lean? Also, how long should I run the setup before inspecting the plugs?

Once again, thanks for all the advice.