Bonneville America Forums Forums Technical Forums Performance Mods TBS vs Thruxton vs Standard needles

Does any one have a photo of a Thruxton needle beside a TBS needle?
('03 790cc America)
I have removed all snorks, cut a round 60mm hole in the dividing wall between chambers in the air box, and tuned to 45 pilot, 140 main, TBS with one small shim. It hammers along no worries (and sounds cool too), but is running a little rich even after I have tuned it in for best available('bout 3 1/2 turns from memory) The pipes have black soot after a ride (unlike my mates with the same bikes) and the plugs come out black - but not wet. I've done 4,300kms like this am obviously I'm almost happy enough.
I'd rather rich than lean of course, but would like optimum tuning, for economy (I hate being the first to switch to reserve on our long rides) AND performance.
If I put the 42 pilot back in it backfires through the carbies (too lean) with them in it sometimes idles high for 10 to 20 seconds or so before dropping to a very low rev. (too rich) I really wish I could get a jet BETWEEN 42 and 45. (Incidently I bought another set of 42's and a 0.43mm drill bit and tried to drill them - there is nothing like factory machining - I was not successful!) If I remove the shim I have a small flat/lean spot at about 1/4 throttle (noticable in top gear on the hiway). If I put the original needle back in I have to add 5 shims to remove lean spots at the same throttle position.
Now to my question - does the Thruxton needle profile lie between the standard and TBS, or is it going to provide more fuel than the TBS.
I could buy the needles, remove a TBS needles from my carby and compare all three types togrther - but before I fork out the cash I just thought I'd check with the experience of the BonnevilleAmerica crew.
Like I stated, I'm happy enough and have had it this way for a year or so - just feel like I might start tinkering again for OPTIMUM.
Does it go like this...
790cc America Needle - more fuel - even more fuel
790cc America Needle - TBS needle - Thruxton needle
790cc America Needle - Thruxton - TBS

Anyone know?

Michael888, This is the question I've been wondering all along too.Midrange Throttle! I've done a little digging and this is what I have so far....TBS needles are tapered but not evenly - thruxton was found to have a markedly tapered needle with much improved midrange flexibility , with no apparent loss of top end power.( compared to a standard Bonneville needle it is not only more tapered but slightly longer.) I've also recieved a post about dyno-jet needles which have a more agressive taper w/ 6 height settings for tuning.That's all I have so far in the real world midrange.

Finally my Harley is going so soon I'll have a Speedmaster...

But I don't understand something you write about pilot jets. I don't understand why you're too lean with a 42 and too rich with 45.

The pilot screw permits to partialize the fuel delivery so a 45 with 1,5 turns on the screw is quite similar to a 42 with 3,5 turns.

In fact when with a pilot screw you are obliged to go over 3 turns, it's better to mount the upper sized jet to have a better tuning range under the screew.

Did someone tell you that the pilot screw must be 3,5 turns open?
Forget it, the pilot screw has to be the position right for your engine and setup. So if 3,5 turns is too rich with a 45 pilot, close it till you'll find good low range and idle speed. May be your right setup is 2,5-2,75 turns out with a 45 pilot.
The right setup for a pilot jet size/screew's turns is when you need choke to turn on a cold engine, and can close choke after about 1 mile idleing (on a middle season spring/autumn).

From lot of reading about this Triumph engine I see they are like a few yars ago Ducati's, where there was never the same jet sizes between two different bikes.

Here ya go Michael:

Bonny, thanks heaps!
EXACTLY what I was looking for.
Thankyou to all who responded.

No-one told me where to set anything.
I basically did the mods, bought all the bits (including some very small washers from my local electronics store (for the shims)) then took to the highway with a small flat blade screwdriver and a spark plug socket. Pullin over to tune the fuel / air screw for "best". Incidentally, "best" was basically just trying to tune out a big lean spot.
Installing the 45 pilots made a huge STEP CHANGE. I realized I'd wasted so much time fooling around trying to tune for all these other combinations.... BUT, It's just that little too rich. Bogs down a bit at idle. Runs rich through out the entire throttle range.... but if I tune it down a little - there it is - my flat spot!
Problem was trying to get rid of it without having so much fuel in other throttle positions that you could actually "smell" that it's running rich. Anyone else recognise that "running too rich stink"? Like I stated, it's pretty good now - just think I'll look for OPTIMUM.
I did not take long to realise that Premium UNLEADED fuel does not allow you to tune a bike as I used to. The bloody plugs just don't change colour as they did!!
Anyway from all possible combinations I got to the point where I am now. No lean spots - a little too rich on idle - and a little too rich at all other throttle positions. If I tune it down a just a bit, there it is .... that annoying lean spot.
Bonny, I'm going to bite the bullet and purchase some Thruxton needles and start the process all over again.
Man, if I had a dollar for every time I pulled these carbies to bits.
Anyone else run Thruxton needels?

I run Thruxtons w 2 shims. I'm rich throughout so I'm going to try the TBS. All of the above is correct. There is a difference in taper and length among the three. I have mic'd the stock and the Thrux's just to be sure...

Thanks for responding.
I'm going to purchase the Thruxtons, then go back to the 42's and start all over.
I did have a good set up with the 42's except for occasional back firing through the carbies when giving a rev while stationary - even with a hot engine. All the mechanics I questioned said my pilot were undersized - and they were right! The 45 cured everyting, except to where I am now - rich throughout! like I said, I wish there was a size BETWEEN 42 and 45.
Will try the Thruxton needles and do it all again with 42's.

YOU will probably have a win with the TBS. ALL engines are DIFFERENT, and here where I am it is always bloody hot - thin air etc.
GOOD LUCK.

You know the more I think of it.... I don't think I can ever go back to the 42's, unless I plug the 70mm hole in the divider plate in the air box. I'm reluctant to go back!

Guitarted, You'll have to play with shimming.
I'm thinking you will get MORE fuel with the TBS, based ONLY on the photos provided by Bonny Phill.

Michael888,just a thought.You are not running the stock air filter I hope.If so you are are too RICH on the fuel.I know dumb question,but you never know. That stock air filter is like a piece of cardboard.I'am surprised they even run with the stock air filters and catalctic converter mufflers.Maybe they come different down under than in the the USA.Good luck.Your fuel is problably better down there too than here.They have us running this gas that's suppose to help clean the air in the southwest desert.Later.Good luck.

Speedblue,
AI gone, lightly oiled Uni filter installed, TOR shorts.

Michael. I turned the airbox into a toolbox, and put K&N pods on. It wouldn't even run with the stock needles, so I got a Dynojet kit, and the needles were perfect. Smooth accelleration right thru the range, with 145 mains, and 42 pilots. The Dynojet needles were longer, with a different taper, with 6 different clip settings for tuning. Just a thought....Oh and the kit came with softer slide springs, for more response, as well. Cheers.

Mine has Dynojet needles in it too...where to they sit in the richness range?

OK. I’ve cancelled my order for Thruxton needles (everything is by order here in regional Queensland) and really want to know more about these DYNOJET adjustable needles.

Who make them?
What is the exact part number?
Where can I get them?
Can I buy just one? That’s a joke!!

Kinda excited by this possible solution.
ANSWER ME DAMN IT!!!!


Does Brent have them?

Brent sells the dynojet kit...don't know if you can buy just the needles, you may hafta get the entire kit.

as far as I know, thrux needles are slightly richer than tbs. maybe one with no shim will work for you
G

For those who are interested.........
I phoned the Australian distributor in Melbourne, who wanted me to contact Dynojet UK? So I did....

I sent the following to

"Dynojet UK Technical Support" <technical@dynojet.co.uk>

To whom it may concern

I have an '03 790cc Triumph Bonneville America.
I wanted to get a few extra horses out of the engine (before playing with the gearing)
I removed all 3 snorkles from the airbox.
I cut a neat round 65 to 70mm hole through the barrier inside the air box (between the two holes where the carburettor intake snorkles were.)
I installed a lightly oiled foam Unifilter element.
I have Triumph Off Road Short pipes on the bike.
After months of tuning I have settled for 45 pilot, 145 main, Triumph Thunderbird Sport needles, with one small shim under each.
The bike runs rich - black plugs (not wet) and black sooty residue in the pipes after a long run.
It took forever to get rid of the lean spot at approx 1/4 throttle - highway speed in top gear.
Changing the standard 42 pilot to the 45 cured all lean spot problems, but now it runs too rich at idle. It will rev high then sink low etc, and on the right day I can smell it is running rich.
The Triumph Thunderbird Sport needles were put in as a hopeful cure to the lean spot. I could tune out the lean spot with 5 small shims under the original needles. But eventually went back to the TBS needles.
Air / fuel mixture screw has varied in adjustment from 4 1/5 turns to 3 during all these attempts. Presently at 3 3/4.
My problem would seem to be midrange. Just can't get a needle with the right profile. Some friends have suggested the Triumph Thruxton needles. They are physically shorter (sit between standard and TBS) but I really feel the profile will be similar (as it was designed for a standard bike designed to meet todays emission and noise control limits - just like the Triumph Bonneville America!)

How can you help me?

This was the response

Hello,

Unfortunately we don't list any off-the-shelf parts for the Bonneville America. My recommendation would be think about getting some dyno time at one of our approved tuning centres, these guys will be able to perform several types of diagnostic runs and tell you exactly what needs to be changed and where, they could even undertake the work for you.

Please visit http://www.dynojet.co.uk/tuningcentres.php?type=1 for a list of approved tuning centres.

Sorry I can't be more help, Martin.

Martin Winstanley
Dynojet UK
01995 600500
martin@dynojet.co.uk
www.dynojet.co.uk

I put in the TBS with one shim today. Feels just about right. I'll have it on a dyno in a couple of weeks and report back.

Do they list anything for any of the Triumph twins? they'll fit.

Michael. I got mine from Serco in Brisbane. Can't remember what I paid for them. Your local dealer up in Gladdy will get them for ya. Serco is a wholesaler, I believe. Check the part # here http://www.dynojet.com/jetkits/motorcycle/triumph.aspx

About the pilot jets:

The reason that these should be selected so that you get the best idle at 2 3/4 to 3 1/2 turns on the idle mixture screws is that they feed more than the idle jets. On the airbox side of the throttle plates, there are 2, maybe 3 holes drilled into the same passage that feeds a gas/air emulsion to the idle jets. As you crack open the throttle, these holes feed gas to the engine untill it is running fast enough to pull enough air to open the slides. It looks like these 'transition' jets come into play again when the engine is running flatout with a heavy load to provide the same function as a power enrichment circuit on a car/truck carb.

So, let's assume a bike is on a good dyno with an accurate air/fuel ratio gauge. If the mixture is off starting around 1500 and starts getting better around 3500, chances are the pilot jet is off size. If the mixture is off above 3,000 and straightens up by 4,500 you probably need to add or remove needle shims. If the mixture is a little off around 3,500 and gets worse as the engine speeds up, you need to change the main jet or change to a different needle taper.

I didn't look well, but have this carburetors the accelerator pump?

It'll be more intersting than full length, to know what diameter are at the same length form top when mounted.

1 cm from top,
2 cm from top,
3 cm from top,
...
...

Usign an arch micrometer like this:

where do you get the tbs needles?

Mechano .... on the accelerator pump.
Unlike the Delorto carbies on my Ducati, the Keihen do not have an accelerometer pump.
The SM/BA carbies are in fact a little "slow". Let me explain.
Most carbies, you twist the grip, the cable pulls up the slide, the engine gets fuel/air. Our Keihen jobs, you twist the grip, the cable open a butterfly, the butterfly allows air in, creates a vaccuum above the slide, pulls the slide up and the engine gets fuel/air.
Having sadi that, they are reliable and extremely common. The Harleys use 'em. In fact MANY brands of bike use them.
I have to keep telling myself, "Michael, you bought a CRUISER!" It's just that it gallops so hard.... you just want MORE!!!

TBS needles are available at your dealer. TBS = Thunder Bird Sport

Bluespoke, thankyou. I will be talking to SERCO in Brisbane.

I've been thinking.
Ramblings....
Triumph put together the BA.
Sized and tuned and fitted carburetters, to a bike with a restrictive air box (to keep the noise and emmissions down.)
I come along and gut the air box and change the pipes etc on the BA, ...now in the tuning of the BA, I fit needles from a bike put together by Triumph (the TBS) with sized and tuned and fitted carburetters, for a restrictive air box (to keep the noise and emmissions down.)
While I acknowledge that TBS and Thruxton needles have worked for others, I've decided to go and purchase some of these DynoJet jobs. If you believe their sales pitch, they have been developed for bikes with some mods done. They weren't taken from a different more sport oriented Triumph bike.

The part number (5120) and data sheet from the web site link you sent me are identical to the US site. The UK site does not even mention the BA!
Please tell me how sucessful these jets / needles / springs are.

I will assume the parts list component "Main Jet DJ116" is simply a part number for the jet - 'cos there is no way that's the size! Right?

My other concern is that the flier says "US MODELS ONLY"
Knowing they run different fuel, and have different emmission laws (although we have taken all the emission stuff off anyway) is there any problem?
Just how well tuned is your bike with these components?
Thanks BLUESPOKE

Michael.

Michael. The Dynojet part Main Jet 116 equates to a 130 from memory. The 118 is a 135, which wasn't fat enough. Mine is a 865, so but from listening to others, the 790 is not much different. Bear in mind I am using the K&N pods, also. After trying various settings, there is no comparison to the stock unit. I rode a mates stock bike he just bought 3 weeks ago, and it reminded me how good mine was, in comparison. Am coming up to Caliope on May 11 for a weekend, so if ya want to have a test ride, that's no probs, just let me know. Cheers.

Michael888

I chainged to the thruxton needles and left 1 shim, and i was getting less fuel econemy when out on a run with tba's and speedies, so i removed the shim and gained 40 to 45km until i hit reserve.

The thruxton needles improved my throttle response a fair bit and helped that little red needle climb over those numbers at the front of the bike much faster than the stock ones.

I'm also running a 45 pilot jet, all snorkles removed, with a hole in the bottom of the airbox, still running a stock filter at the moment but looking at the k&n stock replacement, also need to up my main jet a bit more.and i,ve also opened up the stock pipes with rear baffles removed.

In my opinion with your set up i think your main jet might be little too big.

Do you have the 790cc, or 865?
What is the size of your main jet currently?


Thanks to all who have responded - love these forums!!

Between a new and clean stock paper filter and a K&N filter into the same airbox where air flow is regulated by the same holes, there's not difference in performance.
The only advantage of the K&N is that you buy once and it last for 10 years. The paper filter after 6 month needs to be replaced.

But I don't like K&N filters because they have poor filtering abilities and the engine sucks too much dust.
I prefer foam filter, because it's performance when clean are closed to a K&N filter but with better filtering abilities of fine dust.

Lot of people think paper filters are restrictive. But it's not true. Modern paper air filter are very good in performance and perfect in filtering also the smallest dirt.
The problem is that they are not cleanable and after few months their perfomance drop dramatically and need to be changed.

After 2-3 paper filters you reach the gain with a K&N/Foam filter and with a cleanable filter you stop buying filters.
Just clean and re-oil.

michael888

I,ve got a 790 02 America.

My main jet at the moment is only 125, I,m just guessing but i figure i need to go around 130, 135 max. Your 140 could be the reason of your large feul consumption , but i,d start with removing the shim from the needle take her for a good long ride through the twisties and see how she fares, if your economy doesn't improve much ,drop ya main jet down a size or two, if ya main jet is too big you'll probably get better performance from a smaller 1 anyway.

Be careful about going too small. Lean is bad.

The 140 was in it when I bought it. It was a "demo" model and the one the owner of the store took to work each day. The mechanic fitted TOR shorties to help with sales (get rid of that sewing machine sound!) and so put the bigger main jets in.
It ran fine then.
Since then I've done the air box mods and haven't been able to tune out the lean spot without running a little rich. Like I said it's been like this for a year now, and while I say it does't really bother me, I reckon I'll have a tinker with the DynoJet kit. I'm keen to check out Bluespokes bike when he gets here soon.
I now believe that going from one carbys components (built for a stock noise & emmission controlled bike) to another carbys components (also built for a stock noise & emmission controlled bike) is not my answer - even though it has worked for so many others.
I like the idea of "made for mods" needle profiles.

Anyway, will wait for Bluespoke.

Dog 33 - yes lean is bad.