Bonneville America Forums Forums Technical Forums Performance Mods TBS Questions

These have probably all been answered before but not lately.
1. Guessing TBS is ThunderBird Sport?, do we have a part #?
2. Needles effect the carb performance between 1/3 and 2/3 throttle correct? Or between pilot and main?
3. Advantages/ Disadvantages of needle swap?
4. Why TBS over Thruxton?
5. Quick how to?/ What not to do?
Thanks

1. Guessing TBS is ThunderBird Sport?, do we have a part #?

Yes, it is Thunderbird Sport. #T1241024

2. Needles effect the carb performance between 1/3 and 2/3 throttle correct? Or between pilot and main?


On this pix, the taper/diameter are detremined by which needle ypou use (TBS/Thruxton). The clip position is the same as shims on ours since they do not have moveable needle clips. Adding shims to the needles will accomplish the same thing. Raising the needle (adding shims makes the carb richer in the areas shown)

3. Advantages/ Disadvantages of needle swap?
It helps to eliminate flat spots at different throttle positions. It works differently for everyone it seems. These carbs are a bit fussy about them.

4. Why TBS over Thruxton?
Thruxton is fatter and therfore a bit richer than the TBS. If you want to speriment with needles, get sets of both, try TBS then Thruxton, use the ones that feel the best for your bike. BUT you usually have to drop mains down a size or two as well.

5. Quick how to?/ What not to do?
Carb shimming - but shows the same stuff.

Hey Pat, I ordered the TBS needles after putting on the Freak. Right now I'm running 155 jets and Epcos, and I'm about 2,000 ft in elevation. Not sure how close I'm dialed in to the sweet spot with this setup, and I'm planning on doing a dyno run next month. Was thinking about ordering a couple of smaller jet sizes from Brent to go with the TBS needles. According to the jetting calculkator, 155 jets are recommended with my parameters, but I've read on the forums that I might have to put in smaller mains. Which sizes do you recommend with my setup and the TBS needles? Are needle shims readily available from most motorcycle dealers?(just in case my Triumph dealer doesn't have them in stock).

Sal,
Most shops have the correct shims. You are probably pretty close with the jet calculator, especially with the freak and needle setups, this is where it seems to be spot on.

Well my TBS needles came, and I put them in. Not sure if I can tell a difference between them and the stock needles. I asked if they had any shims, and since they weren't on the microfiche, I'm SOL there. I really need to get a dyno run done, and I'll do that in 2 weeks when I can get a discount rate(still $50, but that's about the best you can do in this town). I'll probably order 150 and 152 mains so I can have them on hand for the dyno run.

I'm not sure if the bike has a flat spot. Looking at other dyno runs for our bikes, you can see how the horsepower takes off above 5,000 rpm, so maybe it's just normal. It's not like the bike bogs down or anything, it's just not as crisp on the accelleration from 1/4 throttle to about half throttle, than it is when you go full throttle up through the gears. I probably won't be totally satisified until I get the big bore kit put in, but that's a year or 2 away.

Just go buy some small SS washers at megahardware store. Even if a little thick they should help since that is where your problem lies. Take one of the old needles to the store and just find little stainless washers that will fit. I believe the shims are .5mm thick?? Izzat right?

Just did some hunting around with the search engine and it looks like they are .5mm thick. Still not sure I even have a problem. Sure wish I could just pop on over to your place and have you ride it.

When you snap the throttle open in second gear, going about 20mph, it should take off like a bat out of hell instantly. If it bogs, putters or hesitates at all, you should add the shims to see if it helps. Shims are by far the easiest to switch as well. Just pull the tank and the tops of the carbs and drop them in. Takes all of about 10 minutes. Can't hurt.
The basement bar is open work nights until 11pm, til sunrise on Tues/Wed, if you're inclined to a loooooong ride.

Quote:

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When you snap the throttle open in second gear, going about 20mph


From the guy who made the thread:
IT's THROTTLE POSITION - NOT RPM! NOT SPEED!!

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Hmmm Uncle Pat must be sampling the brew again.

But that is throttle position, WOT!
Yutes.....

Dinqua,<Buster of light Beer>
I just tried the 20mph roll on in 2nd gear.
The bike did not run like a bat out hell.
It pulled fairly well to about 5000rpm then took off like a bat out of hell to redline.
I guess I have some more work to do.
2004 Speedmaster.
AI removed.
TBike pipes.
130 mains.
Unifilter & Airbox drilled.
Thruxton Needles,no shims.
17t front sprockett.

I'm gonna go out on a limb and say the Thrux needles are too rich, but just a gut feeling. I'll let Pat confirm my natural talents.

That's not a long ride, that's an adventure to get from my place to yours.

I'll give the "whack the throttle in 2nd gear at 20 mph" a try tomorrow and see what happens.

dowop, Go back to stock/TBS needles and try again.
Try it without shims first.

Dinqua,You think I should try the stock needles again even after the good dyno run?
I would think I might be to lean with the airbox mod.
If you think I should I will try it.
Like you said it is a quick fix,as long as I dont have a problem with the Diaphrams moving.
They can be a beer.
I mean bear.

The good dyno run meant you have the main jets perfect. Now you need to fix the midrange, this is where the needles make all the difference in the world. Start with the TBS with no shims. Then try them with 2 shims to see what your butt dyno tells you. If there is no significant difference, from the Thrux vs TBS, stick with the TBS for better fuel economy and maybe even add a third shim to each.
A perfect dyno curve should show HP as a constantly upward angle, sorta at 45º, but a steady climb at the same angle. Then torque should rise quickly and remain flat across the entire throttle/rpm range.
The torque curve is best for doing fine tuning as you can adjust the areas with dips by adjusting according to the above picture. Notice how the needle stuff is pretty much the 1/4 to 3/4 throttle range?
Ok, carb school:
Think of the diagram as the torque curve from a dyno, you want the torque to be flat from say, right above the area where it says "pilot jet". Forget about the bottom throttle position for a minute, imagine it is linear and your torque curve instead, rpm increases as you go to the right. Sort of like holding the dyno torque printout over the top of the diagram. Work with the parts that are lower in the dyno torque by adjusting the coresponding carb parts listed in the diagram above.
Now, say you got a dip in the torque around the middle of your rpm, same as the middle of the picture (1/2 throttle area) see how the needle taper and needle clip control ALL of this area. Now take a close look at the stock/TBS/Thruxton needles side by side, notice the taper and LENGTH of the different needles. The TBS and Thruxton needles are about 2 shims longer than stock, so adding 2 shims will get you closer to the common reference of clip position, then by changing between TBS/Thruxton you can see the taper is different. The TBS have more of a taper, but less diameter. So it's kind of a guessing game until you get your specific carbs to be in the happy zone. Notice the diameter has more to do with the lower areas too?
Does that make sense to ya?
Another example: say your torque curve dips in the lower ranges even more, then you would diddle with pilot jets and needle diameter, Thruxton has the advantage down there where TBS needles help more in the 2/3 to 3/4 or mid to high rpm ranges.
It ain't rocket scienbce, unless you want it to be.
You can get the bike to run just fine by just swapping the jets, but playing wiht jets/needles/shims and you can dial it in and get another 10% HP and torque which will also be the most effecient use of fuel as well.
But then again, if it ain't broke, don't fix it.
I diddle, well, cause I can.

Pat... when the heck are you just going to say "hell with it" and open a shop? I'll ride my bike from Virginia to New York just so you can work on it.

Thank you,
I am off to the garage to tinker.
It is around 90 here in NE Ohio so I guess I will take a 24oz can with me.
Thanks again Pat for the detailed answer.
I just might drop off a keg of Bud Light to you.

So you listen to Pat when he tells you the same thing i did which didn't have you trying the TBS, eh ! Ok, now i know where i stand. seriously, try the TBS with one or 2 shims! Or are you still having that problem with dying at the limiter?

Pat.....thats basically what i did. the thruxtons were a bit too rich, and the TBS with 3 shims were almost exactly the same length. so i tried the thruxtons and the TBS with no shims, then the TBS with 3 then 2. And by the way my pipes and air mods and mains are identical to dowop's.

I found the truxtons with no shims were very similar to the TBS with 3 except the thruxtons gave me a tad more off the line while the TBS with 3 gave me a tad more during street speed roll-ons. the TBS with no shims gave me the same performance as the stock needles with 2 shims. So i left the TBS with 3 shims till recently when i removed one and found they gave me a little better performance with 2. But the big change going to 2 on the TBS was that with 3 shims or the thrux with none both caused a problem where when i'd hit the limiter the bike would die for literally 10 seconds or more, sometimes bringing me to a complete stop. Going to 2 on the TBS completely eliminated that and now it just cuts for a split second then resumes. i know that may sound odd, but i assure you it's true. Now i'm thinking of removing one more shim, but the thing that makes me a bit shy about doing it is that it would only be one shim above none where the TBS gave me no performance benefits over mt stock needles with 2. but i'll probably try it. Could be a sweet spot there. The only reason i haven't so far is it's such a pain to do it and if it's not good i'll have to do it twice to go back to 2 shims. Mainly because sometimes the diaphrams come out of thier races and there have been times where it took me a very frusterating 1/2 hour to get just one back in.

I have an 06 TBA with air box drilled, snorkel removed and 2 rear baffles gone with the third baffle drilled.
At about 3/4 and up throttle it feels less responsive than at 1/2. Kinda like dead after a certain point. According to the chart you posted, that probably indicates I need larger main jets...sound right???????

Dazco,
I did follow your advice & went with 2 shims with the TBS.
I had a heck of a time to get the diaphram in right.
Finally had to put one of them in a freezer for 10 minutes.
The Dealer helped me out with that problem.
The bike did not seem to run any better so I went back to the Thruxton needles.
I just tried the TBS with one shim.
I dont notice much difference except when I hit the limiter it was`just a sputter instead of dying.
I am going to schedule another Dyno.

Yes, but thats why i told you to try the TBS in the first place. remember you were telling me about the bike dying at the limiter and i told you the TBS would probably remedy that because it did for me. I think if the bike doesn't dyno quite as high you should still consider leaving them in because that limiter problem just isn't right. Then again it's your call as to what matters most, but personally i'd be willing to lose an almost un-noticable bit of power to lose that limiter glitch. By the way, good tip on the diaphram.......wish i'd have thought of that when i spent a 1/2 hour once trying to get the frweakin thing in !

If you have stock jets, try 125-130 and start low

Daz I am running stock jets at this point. I used Pats jet calculator and it recommended 130.

Pat...thanks for the response, I will be ordering from NB.com tomorror what I think I need (130)

I just turned out the pilots 3 turns and all my popping seems to have gone away and I notice better lowend response.

Daz or Pat,

Is it necessary to pull the carbs for main jet replacement? It seems the right carb is readily accessible but the left is questionable. I was wondring if anyone has rejetted without pulling them.

Yes, i never pulled the carbs and i've removed the bowls to change mains many times. It's just a matter of figuring how to het your hands in there best and most importantly getting allen screws to replace the phillips head screws. I can remove and replace the bowls now in about 15 minutes which is a far sight better than how long it will take to remove the carbs.

Thanks Daz...I was hoping to here that. I was going to order the allen screws with the jets so my next time would be easier. I thought if I was careful and used the right tools I could get to the jets. The right card is a no brainer, but that left one looks a little tough

Phil,

I agree, I thought I would go with the famed jet calculator and put in the 130's it recommends

Those friggin carbs screws might give you problems getting them out. Definitely order the screw set from Brent. Use some needle-nose vice grips if any screws strip...

DW,
Just be sure you have a good tip on the screwdriver as those screws strip very easily. Use a little socket type if you can to get better leverage. And be sure to drain the float bowls first too. Then be sure to tighten the drain screws when you're done.

I did almost 200 miles today.
Rode over to Nw PA Allegany Mt region.
Bike ran great.
I am running the TBS needles with 1 shim.
I hit the rev limiter a couple of times.
It just barely sputterd.
The 20mph roll on pulls great all the way to redline.
Actually it did not kick in to around 7700 rpm.
Thanks Dazco & Dinqua.
Dinqua is closer so I can deliver some Keystone Light over his way.
Dazco, when I make it out to LA you will receive a case of Corona.

Thats good to hear. I fugured your bike couldn't be so much different than mine that it wouldn't respond the same.

I did the 20 mph 2nd gear roll-on and I still can't decide if it's dialed in or not. It doesn't quite have the pull if I'm already at 1/3rd to one half throttle. Oh well, guess I'll find out when I take it in to get it dynoed in 2 weeks.

what are your mains

You ever notice how all them zoom-zoom adds give us how much more horsepower their units will provide but FAIL TO INFORM ABOUT DESCTRUCTION OF GOOD GAS MILEAGE!!

I had Cobra pipes and re-jetting done to my 1995 Honda 1100cc (which I recently traded in for my ’06 TBA) and while the sound was nice and loud, the mileage dropped from 57.4mpg (yearly avg.) to 41.2mpg.

If I had known I'd lose 28% of my MPGs I'd a never had the stock gear removed.

My 2¢ rant.

Not mine. I gained probably 10 HP with my mods and my milage went up about 3 MPG. It should not go down because the bike is getting more power out of the mix, so if you ride the same you should get BETTER milage. Problem is, once people get better power they tend to use it of course.......why else do it? But if you drive it the same as you did before you should see better numbers. When i ride like i did before the mods i get better milage.