Slide spring physics 101

[dtkid]

It has been many moons since I had course in spring-dynamics, so I must ask the gurus.

Would simply decreasing the length of a slide spring (cuttin 25% off) be comparable to using a smaller diametere spring. Or do factors such as pre-load and after-load make it impossible to alter spring behavior/tension by simply using a shorter spring?

[RJ]

When comparing 2 springs it will be the differences in the thickness of the wire the springs are made of, the distance between the coils of the springs, and the metal the springs are made of that will determine which spring is harder to compress (or stretch). I'm not so sure the diameter of the spring itself is that much of a factor.

[Mike_H]

What are you trying to accomplish with a smaller diameter spring? Changing the length will affect preload. Spring force (F) = displacement (x) times the Spring constant (k). K is determined as RJ said. Mat'l properties, and the geometry of the spring. It is constant.

If there is preload on the spring to begin with...then yes, cutting some length out of it will decrease the force that it exerts in the same range of motion. Cut too much though, and you could end up with a floppy assembly.

What are you specifically trying to do. Is the "slide" spring in your carb? Is it acting in torsion, extension, or compression?

[Billy Ricks]

What are you trying to accomplish with a smaller diameter spring? Changing the length will affect preload. Spring force (F) = displacement (x) times the Spring constant (k). K is determined as RJ said. Mat'l properties, and the geometry of the spring. It is constant.

If there is preload on the spring to begin with...then yes, cutting some length out of it will decrease the force that it exerts in the same range of motion. Cut too much though, and you could end up with a floppy assembly.

What are you specifically trying to do. Is the "slide" spring in your carb? Is it acting in torsion, extension, or compression?

I guess throttle response is what he is trying to improve. You have to be careful though. Jet kit manufacturers match spring weight to the jetting of their kits and the size of relief hole that you drill in the slides. You can really lean a bike out by lightening spring tension without having the proper size hole in the slides. Less tension against the same vacuum as before will pull the slides up higher than with the proper springs.

[KEITH KRAUSE]

I'm no expert at spring dynamics, but cutting the springs would ruin them in my opinion.

[dtkid]

Thanks guys for the input.

I have been trying a bunch of different things on the carbs of an 81' GS750.

For the most part....just trying to develop a better foundation of knowledge.

I have a bunch of different springs (so I can afford to screw some up) and I have been using different combinations of jets, air-jets, springs, slide-hole diameters, etc.

One goal is to be able to put a set of carbs together from stuff I have and not have to purchase anymore Dynajet kits (of which I have already purchased three). I do alot of work for people around here (home) and most don't have the money to go out and buy the kits and pods.

I am not necessarily trying to boost performance by any means, truly just trying to find working combinations that provide rideable/dependable power throughout the rpm range. And when somethin' don't work....I gotta know why..

I know what I am doing is exactly what the engineers at the factory did to begin with, but I don't always have the factory parts.