Triumph Rat Motorcycle Forums banner

1 - 12 of 12 Posts

·
Registered
Joined
·
1 Posts
Discussion Starter #1 (Edited)
Hi everyone,

I am planning the following modifications on my stock 2003 Bonnie T100 (790cc):

  • Air: Remove both snorkle and airbox baffle, max out the cover hole, fit a K&N filter
  • Replace the existing needles with Thruxton needles and use shims to raise it by 1mm
  • Shorten the carb springs by 1,5 turns
  • Widen the slider hole from 2,xmm -> 3-3.5mm
  • Replace the main jets
  • Add Norman Hyde togas with muters
From what I understand, this is a kind standard performance mod for the carb bonnies. HOwever, I got 120 jets with the kit I bought. Are these 120 jets really large enough? I heard of people in other forums recommending main jets up to 132 with this setup.

I wonder with which jetting everyone ended up with this setup?

Thanks,
Jimbo
 

·
Registered
Joined
·
1,415 Posts
My 08 T100 (865cc) has about the same breathing mods as you have. Start with 135 Keihin main jet, Thruxton needles, no shims, OE 40 pilot jet. Do NOT cut/shorten the springs, the PO had removed one coil on my springs, unbeknownst to me, it only complicated jetting. Had to buy new springs to get it right. You may want to try one shim after testing for performance and fuel mileage, mine dose best without the shims. This should get you in the ballpark.
Happy motoring !
 

·
Registered
Joined
·
2,049 Posts
I too have the thumbscrew idle screws (New Bonneville style), thrux needles (no shims) and 135 jets. I worked up to this jetting step by step, 2.5 increase from 120 to 135. I didn't modify the springs or open the butterfly by drilling any holes in the flap. I did end up with 42 pilots to finally get rid of the popping on over-run 2003 796 baffle removed snorkle gone K&N filter
 

·
Registered
Joined
·
427 Posts
Hi mate,

790 ‘04 Bonnie:

I have 145 mains 42 pilots thruxton needles (no shims), snorkel and baffle removed with a DNA filter, fire starter mapped ignition (and red line moved to 8000rpm) and blue flame coil and posh plugs. This all mates to a free breathing TEC 2 into 1 with a performance baffle (lovely sound). The jetting set up took ages, I found little changes were best and took my time to get there. I put the thruxton needles in on a whim and am really pleased with the huge mid range throttle response although I did need to up the main jet.

I don’t know about shimming thruxton needles; I’d be keen to hear your results..

Mine positively flies in comparison to where it was; she also fuels beautifully off and on the throttle and rarely hesitates. I quite like a little lean condition on the over run (a little popping is quite characterful when rolling off the throttle, loads sounds a little ropey... ) but this could easily be dialled out if I wanted to..

I hope this helps..


Chris
 

·
Registered
Joined
·
4,960 Posts
When I was running stock carbs (08 T100) the only jetting I changed was the main jet to a 145. The bike pulled clean from the bottom to the top of the rpm range. I have and had Dominator Touring exhaust, TPUSA igniter, 4 in long Uni pod filters and a TPUSA airbox removal. I also only live about 500 ft above sea level.
 

·
Registered
Joined
·
427 Posts
When I was running stock carbs (08 T100) the only jetting I changed was the main jet to a 145. The bike pulled clean from the bottom to the top of the rpm range. I have and had Dominator Touring exhaust, TPUSA igniter, 4 in long Uni pod filters and a TPUSA airbox removal. I also only live about 500 ft above sea level.
Im considering getting rid of the air box; did you loose any midrange when you did it?
KR


Chris
 

·
Registered
Joined
·
152 Posts
Im considering getting rid of the air box; did you loose any midrange when you did it?
KR


Chris
Jenks bolts suggest that one should enlarge the vacuum hole in the bottom of the throttle when removing the airbox and using separate pod filters. Anyone did this? I havent yet. Supposed to improve throttle response.
 

·
Registered
Joined
·
2,585 Posts
Don't drill anything.


I have a stock 2005 with similar breathing mods. I just bafflectomied my stock pipes and gutted the airbox and put in a K&N filter. I did not drill anything in the carbs, I did not cut the springs. I think those two things are a bad idea and even risky. I installed 135 jets and Thrux needles with 1 shim 30,000 miles ago. The bike runs cool, pulls very strong. Mileage dropped to 40 mpg. I suspect it is slightly rich but that makes the engine cooler and makes it last longer.
 

·
Registered
Joined
·
152 Posts
Don't drill anything.


I have a stock 2005 with similar breathing mods. I just bafflectomied my stock pipes and gutted the airbox and put in a K&N filter. I did not drill anything in the carbs, I did not cut the springs. I think those two things are a bad idea and even risky. I installed 135 jets and Thrux needles with 1 shim 30,000 miles ago. The bike runs cool, pulls very strong. Mileage dropped to 40 mpg. I suspect it is slightly rich but that makes the engine cooler and makes it last longer.
No, i think it seems like a ridiculous, non reversible mod. Its got good response anyway so im not putting a drill to the slides!
 

·
Registered
Joined
·
116 Posts
Hi everyone,

I am planning the following modifications on my stock 2003 Bonnie T100 (790cc):

  • Air: Remove both snorkle and airbox baffle, max out the cover hole, fit a K&N filter
  • Replace the existing needles with Thruxton needles and use shims to raise it by 1mm
  • Shorten the carb springs by 1,5 turns
  • Widen the slider hole from 2,xmm -> 3-3.5mm
  • Replace the main jets
  • Add Norman Hyde togas with muters
From what I understand, this is a kind standard performance mod for the carb bonnies. HOwever, I got 120 jets with the kit I bought. Are these 120 jets really large enough? I heard of people in other forums recommending main jets up to 132 with this setup.

I wonder with which jetting everyone ended up with this setup?

Thanks,
Jimbo
Hey
How did you arrive at your suggested jetting decisions?
To answer your question, 120 is probably too small if you modify the airbox for more air.
Based on your suggestions I would imagine mains between 125-130 will be what you're looking for but I'm not entirely sure what removing the baffle does to airflow although I'd imagine it probably causes turbulence.
I have an 2001 that I bought in 2003 and I've probably forgotten more over the years about jetting than I remember but thinking back I seem to remember not a good idea to modify the airbox. Removing snorkel is fine but if you are going so far as to remove the baffle then you may as well remove the airbox altogether and fit pod filters.
But I guess you can always try it without baffle and see where it takes you.
Thruxton needles have been used with success by many but the main jet sizes vary based on individual experiences of running their bikes with different airbox mods, main and pilot sizes and different exhausts. I've seen results anywhere between 122-145 (which seems crazy) but you can never say anyone is wrong without dynoing the bike and measuring mpg and air/fuel mix in gases.
If your pilots are less than 2 turns out they're too big and if they are more than 3 turns out they're too small and they will greatly affect you in cold starting.
Figuring what mains you need is a far more 'seat of pants' experience from riding and searching for your flat spots/power bands at different gears/rpms.
Drilling the slides is imo something to only do under good advice when you know its gonna fix a problem rather than create one or you know for sure you absolutely need faster slide response to remedy something.
If you do decide to drill it do not go larger than 3mm.
Springs I can't comment on.
To give some basis here my bike was professionally setup by Mecatwin France with bellmouth intake, k&n filter, airbox intact, 40 pilot (2.5-2.75 turns out) 122 main, their own needles (more like Thrux needles than Bonnie) slides drilled to 3mm and Mecatwin free flow exhaust, its probably similar to NH toga in terms of flow.
It runs beautifully without flat spots or popping.
I don't know how experienced you are but before doing anything I would read the jenksbolts carb tuning notes for Bonneville and also their carb theory 101 sheet, you can find them online.
Also check out this guys experience with several carb jet/needle/slide setups - there are 3 or 4 posts on his blog.

It's a step by step process to arrive at the ideal fueling and it can be fun but many ppl have screwed their bikes by not approaching the process properly.
Here's wishing you success?
 
1 - 12 of 12 Posts
Top