Bonneville America Forums Forums Technical Forums Performance Mods Mucked around with Carbs and need some advice

I've been loitering around looking at info here for what to do to my TBA to get the best or better performance.

Firstly, I'd like to thank all you guys for the info being shared and I finally plucked up the courage and got rid of the snork, fitted a unifilter, rejetted to 130's (pilots still stock 42?), fitted 1 shim and for tidyness, fitted a rubber v/stack on the airbox inlet (Just looks neater).
I re balanced the carbs and set the screws at 2 turns out.
Bike came with long TOR's and had the AI taken out by the dealer from new..

Road tested today and found it hesitant to pick up from 2500/3000 revs, felt like a real flat spot in any gear. Above that the bike pulled fine and top end is definatly stronger.
Problem I have is I like the bottem end tourqe and I can't help feeling I've made it worse.

Any thoughts? Is 130 without any airbox mods too much? Would 130 mains affect the low rev responsivness? Would taking the shim out improve it or add another?

I have some 125's and more shims and will probably experement a little but thoughts from the experts (those already battle scarred...), would be much appreciated.

Try this: Pat's Jetting Calculator.

oh, and this: Throttle position - not rpm's

My rig is similar to yours. 03 TBA with AI removed, and long TORs. I have 42 pilots, 120 mains, no shims, and 3 turns on screws. My unit runs well with a slight flat spot in midrange. It runs poorly at full throttle with snorkel removed (lean) so the snorkel remains with jets ordered. My plugs confirm this. I installed 1 shim and this helped my flat spot but still need larger mains. Have 125 and 130s on order. Will keep your informed of my progress.

What throttle position are you in at the problem rpm? If your full throttle is fine, then your mid range adjustments need some fiddling. I'm assuming you are a bit lean in the midrange still. TBS needles with no shims help the flat spot. Increasing your idle screws will help. You could add another shim to your current setup also. Keep us posted (so I can copy).

Larry, sounds like your setup is very much similar to mine with the only diff is that I drilled both my airbox and filter and I have the TBS needles. All that I can say is that mine runs very well, I get excellent milage and my plugs look good. Mind you when I do my 20k svc I'm just going to take out the shim cos I have tbs needles but if you do drill then your shim should be right.

You've probably gathered this already cos of Pat's calculator and of course if you don't want to drill then 125's look the go.

I don't know whether you have hesitations towards drilling the airbox and the filter but I haven't had a problem so far and that includes riding for several hours through torrential rain. Anyway that's my limited amount of experience talking so hope it helps

I'm thinking 130's are to rich for the pipes...your air box isn't drilled so you're not offsetting the 130's with enough air...drop to 125's

Thanks all.
I swapped for 125's and the difference is huge, pulls fairly strongly now from 2000 without the soggy feeling I was getting. Maybe I was getting a little greedy with 130’s...?
I'd originally planned to remove the airbox baffle but it doesn’t seem to have a removable restrictor, certainly nothing like I’ve seen in pictures here.
There is a bulkhead immediately next to the filter with square apertures, just before the air flows into another chamber leading to the inside of the carb inlet bellows, but this is part of the box moulding. The America is a '07 model, perhaps they’re different.? I’m a bit reluctant to hack away anything until the warranty ends, so this will probably do for now. Maybe I’ll can the box for a freak over the winter.

Also went for 2.5 turns out but I'm not sure this is just right yet.

For info, I pulled the plugs last night before hand and they we're as black as Newgates knocker..(Sorry, Brit thing... ), so the advice on being rich was spot on.

I've used Dinqua's site for a lot of info and found the step by step instructions a great help. (Forgot about the Jet program though). Thanks D!

Been a pretty good day so far,…. With your help I’m back running properly, I also found out that the float screw I thought I’d stripped, hadn’t and Man Utd won there first game of the season… What more can you ask… Thanks Guys.

only the earlier models had a second set of snorkels in the
airbox, one in each of the holes leading from the filter section.
most of the later models had only the top snorkel

Larry,

I found the same thing with the short TORs. 125 main jets actually work better than 130s. But you should definitely try the TBS needles, they fatten up the mid range nicely. Right now I am running Short TORs, Uni-filter, drilled airbox, 125 main jets, TBS needles with 1 shim, 3 1/2 turns. That combo is working pretty well.

I may try Thruxton needles to see if there is any positive or negative difference. We will see.

I have a similar set up to you although the bike is an 04 TBA. Last week I decided to do some work on the carbs, so I spoke with the chap at Jenks Bolts. He suggested pulling all snorkels out (mine has 2 inside the box) going for Thruxton needles and 120 main jets. I have long TOR pipes AI gone and a K&N filter. Like you I did not want to hack up the box although I may do in the future. Anyway after dropping the bowls off I found I already had 120's in so just put the needles in with no shims and took her for a spin. Firstly the bike was a good bit noisier but a nice roar and the power increase was very noticable especially at full throttle. No flat spots good colour on the plugs and a bit of lovely popping on overrun when warm. So I am well pleased and will just leave it as it is. Hope this helps...I think the main difference is the Thruxton needles. I never touched the mixture screw as it seems fine.

I have been told the profile is better on the TBS needles than the Thruxton where our bikes are concerned.

If you never touched the mix screws you're likely very lean at idle (this won't show up using the color check) ESPECIALLY if you pulled the snork! They come lean from the factory to pass EPA standards... you'll find the popping will decrease (but it won't go away completely)your needles sound like they have richened your stock mains just about right...thruxton needles are very rich running... more than TBS or stock

I know, I know.. Forever tinkering, but I’m gradually getting there…. I think!.

Still have the 125 mains, one shim and tried to adjust the screws from my guess/starting point at 2 ½ out. Checked the plugs beforehand and one was perfect the other really black, yet the screws were set the same..?
Anyway, I read somewhere that the final setting may be different for each carb and therefore tried to set them on 1dle (1000). I’ve turned them out independently until reaching the best idle (after which point turning further makes little difference). Now one's at 2 ½ the other at 2 ¼ . Is this the right approach?
I know this is basic stuff to you guys but I’ve struggled to find the best setting. Is there a knack to it? Am I missing something or as my other half has pointed out for years, clearly deranged?

More Q’s sorry.
Reading the comments here I think I'd like to try different needles. TBS seems to be the consensus?
Any ideas where I can get these in the UK? Jenks has Thruxton listed, would these be that much different and would they be worth a try over stock on an 865 motor?

Read the thread about throttle position…(Couldn’t agree more). It’s the ¼ to ½ position I’m looking at to be as strong as possible. ½ to full is good.

As ever, your help much appreciated.

Larry

TBS (ThunderBird Sport) are a Triumph dealer Item...just remember you only need two (the Thunderbird has three)

The Freak kit came with 160 jets. The calculator says 154 jets for my setup. Will it make that much of difference?

Mine was too rich with the 160s

ditto on that mine was too rich too so was Wendys.

How do you know if it is too rich? What are the symptoms?

WOT????

Wide
Open
Throttle

I'm getting stumped now.
Tried setting the mixture screws several times and i'm sure 2 1/2 is right, but I'm still getting one plug (Right hand) really black and sooty the other's perfect.
I'm thinking of pulling the carbs and re assembling jets/needles Etc. Any ideas what might be causing this difference and what to look out for?

Cheers

set your screws by ear...

pull one plug wire...then turn the screw all the way in till it starts to die...then turn it all the way out till it starts to die about 1/2 way between these two "starts to die" spots is about right...

then repete on the other side...

Thanks Rob.. Did as suggested and 21/2 and a bit works well now. Also found some gunk in the jet carrier. Not sure how but after a run today everything is sweet again and plugs as Mr. Triumph intented.

Thanks guys.

Finally, good on ya. Now get out there and ride it!

Bit off topic but another month and the snow will be starting!winter project 07 speedmaster and with these forums,I have no quams about going at it,I have learned more than I could possibly imagined! just tippin my hat!much appreciated.

Ok... Just put in the TBS needles (no shim) and dropped down to 150 jets...The screws are still untouched and so are the pilots... The bike feels better but I still have a flat spot spot in the 3000 - 3500 area... I plan on turning the screws a bit(all the way in then back out till they sound right) Any other suggestions?

Also... Would love to meet up with anyone from the Tri-State area. I have not seen many of the these bikes around never mind a modified one that I can compare to and someone I can collaborate with. Not to mention RIDIN

Ok... Just read Dinqua's rant on throttle position so I need retract a statement.... the 3000 - 3500 rpm weirdness is really happening during the first quarter turn of the throttle. So it is not gear specific. But I tend to be in that range when coating while in traffic so I am probably already a gear too high BUT I figure the bike should be as responsive at this position/rpm

Need to balance the carbs and take another reading. This can get deep (or long), but if your just riding along and easing back to the house and checking the plugs, you are going to have a hard time finding the rich and lean points. Pat (Dinqua) is right on with all his info, but when checking the plugs you need to chop the throttle and check them. that means take the bike out (mark the throttle) and run it a mile or so at 1/4 throttle. Grab the clutch and hit the kill switch. Pull over and check the plugs. Thats a throttle chop. Do it at 1/4, 1/2, 4/3, and WOT (or save yourself a ticket and use a dyno). Any gear works.

But, above all, balance the carbs every time you make a change. My left carb is a 1/4 turn richer than the right.

According to the Jet Calculator I should be running 151.5 mains. Changing to a more free flowing exhaust only increases that number. Looks like the FREAK provides a bunch more air than UNI since those calc out to 121.5. Big Diff.

Anyway as my signature states. I have FREAK/150Mains/TOR Shorts(STOCK)/AI OUT/Stock Pilots(42)/unturned screws. I will be turning them soon. I just purchased the CARBTUNE II so I will be mucking around when that shows up.

Maybe I am just a bit paranoid about all of this since I am changing so many things...

PLus I am a Perfomance Analyst on computer systems so the DYNO I have is driving me crazy Refer to NH DYNOS (finally)