Bonneville America Forums Forums Technical Forums Performance Mods Lighter carb springs

Does anyone have the correct part number for the
lighter carb diaphram springs? I had gotten a number
from one of the posts here but the springs are a little to
large in diameter to fit so obviously they aren't right,
though they do have less tension on them.

Bumping this one back to the top,
I want the part number too.
I believe greybeard has it?
I was sure someone said the CV40 springs fit, never actually seen it so I am not 100% positive.
Come on, who got it?

I tried the Screaming Eagle CV springs. Unfortunately they were the wrong diametre and length. I seem to remember someone using Kawasaki springs...

Edit: Found it! Boof on Delphi posted this long ago:

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I managed to find out some more about the lighter carb springs,they are from a FZR1000 and you just cut them to the same length as the ones you removed from the TBA carby.

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..and it was from a Yamaha ;-)

Call me goofy, but what is the advantage of lighter springs?

It allows the slider in the carb to rise more quickly for better throttle response.

I thought that would be the answer, but wasn't sure... Carbs are a little more black magic than science to me- but I'm working on it. thanks

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You just cut them to the same length as the ones you removed from the TBA carby.

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and remember to put the end you cut DOWN in the carbs so the factory flat end will be in contact with the tops of the carbs for positive surface contact.

Makes sence. Thanks for the tip! Now let's see if the yamahondasaki dealer can get me a pair of springs...

I don't have the part number. I've only had one other bike that came with a jap carburettor. It promptly fell apart, so I tossed it and got an S&S. Have I ever mentioned that I am not terribly impressed wit Japanese "quality"? If I ever come across a US or UK made carb that will fit this engine, I will do anything necessary to change over.

Greybeard, tell us how you really feal, only this time don't hold back.

Edelbrock bike carbs, oh great Bearded One.....
(Good enough for a Harley, so should be good for a Turnip, too.)

PapaDean,

I'm thinking you've got something there.. After 2 years of reading all the "Needles/Shims/Jets/" posts on here and the resulting "work/don't work for me" posts, plus my own limited experience, I have come to the conclusion that these carbs are merely servicable. They are not "precision made" by any stretch.

I get the feeling they have a wire basket near the assembly line where someone dumps a fresh load of carbs every hour or so and they grab 2 and bolt them on.

If these Edelbrock carbs could be fitted without too much modification, I would bet they would make 1 helluva difference in performance and eliminate a lot of the trial and error mods we all seem to go through.....

Hey Greybeard...then you'll be happy to know that Jenks is or was testing new Amals on his Bonnie.
From the NTBF...

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8928.1

A New Bonneville ran today with a pair of 36mm Amal Mk2 Concentric carburettors – and it was GOOD. With a pair of carbs out of the box, fitted with 300 main jets, 25 pilots and a No 3 cutaway slide the bike started first turn and I rode 25 miles on the first test run:



How was it?



Well, the good news is that between 3000 and 5000 revs the bike pulls like a train and the throttle response is instant – more like FI than CV carbs: really impressive. I couldn’t go above 5000 because the first set of cables made have too much slack in them so the carbs do not open fully. Also, the carbs need setting up to give a better idle and even tickover: clearly more work to be done. The next stage is to get a bike fitted with the carbs up to the dynamometer to see just what can be achieved with a good set up.



The installation is neat, looks good and uses the stock airbox and inlet manifold rubbers. We plan to offer a bolt on kit, complete with cables and all jets needed for the most common Bonneville and Thruxton exhausts.



More news as it develops: but the first step has been taken!



Peter

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Found this page with some good info on Amal carbs for anyone who is in the dark about them.

http://www.sterlingmotorworks.com/tech_tips