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.
