So you wouldn't want to cut the DJ springs?


edit: airraptor I did a few searchs and came up with nothing. Do you know what I should search for, specifically. I tried just your name, that was SSLLLOOOOOWWWWWWWW, so I searched for your name in the aurthor and carbs in the title or body and could find anything.

 

Coil Springs 101:

Cutting coils off of a spring will shorten and STIFFEN the spring tension. The load is spread over a shorter distance. On a thin coil spring like in a carb, it can just be stretched slightly, but it shouldn't be an issue. On a suspension, it can have a dramatic, irreversible effect. To lighten spring force, either use a spring with a thinner dia. or VERY CAREFULLY grind a small amount of material from the outside dia. of the spring. To get multiple rate springs, either the coil is made of variable dia. material or multiple springs are stacked for long travel suspensions.


So now I have a few questions. Stiffening the throttle spring is a good thing to keep the slide from bouncing. This is gonna add more strain to your thumb throttle.

1. Anybody recommend a good replacement thumb lever, or is it better to go with a twist throttle?

2. Why do a few websites recommend lightening spring tension if it can lead to increased slide bounce?

3. Spacing the carb further from the head - what's the best method to do this? Does this require a longer throttle cable?

4. Would the carb spacing, spring stiffening and internal carb mods be worth doing on a piped Rap, or is it better to just do it when compression is raised or motor is enlarged?

 

<u>Coil Springs 102</u>: For a given spring, the spring rate (force/displacement distance)is a constant characteristic for a given spring, sans a new spring rate after permenant deformation has occured (stretching the spring). So cutting coils from a spring does not change this rate, it only changes the potential force that the spring is capable of loading up to. If the spring is supposed to be set at a certain compressed length it *may* exert less force if the relaxed spring length is shorter before displacement occurs (such as cutting off coils before squishing it).

So, NO, cutting coils off of a spring does NOT stiffen it...

(edit: corrected choice of words, changing *may* for *will*)

 

Has anyone tried a crossover tube on the head side of the carbs?

 

Or a 2 into 1 and back into 2 (from the carb too the head). This should improve fuel atomization. I may have too fab something up for some testing. Same principal as the extension....more volume.

 

Hhmmmm...

Coil Springs 101, session 2.

The following is from a website on coil spring design. Coil Spring Design

"There are three basic principles in spring design:

The heavier the wire, the stronger the spring.
The smaller the coil, the stronger the spring.
The more active coils, the less load you will have to apply in order to get it to move a certain distance.

Based on these general principles, you now know what to do to change the properties of a spring you already have. For instance, if you want to make automotive valve springs a little stronger than stock, you can a) go to a slightly heavier wire and keep the dimensions and coil count the same, b) decrease the diameter of the spring, keeping the wire size and coil count the same, or c) decrease the number of active coils, keeping the wire size and spring diameter the same. Naturally, you can also go to a stronger material to achieve the same result."

By cutting coils, you are decreasing the number of active coils and increasing the force required to compress the spring. This is independent of coil size, wire dia. and composition.

So back to my original 4 questions... any suggestions?

 

<u>Coil Springs 102, session2:</u> For a given spring, the displacement required to obtain a certain load does decrease if there are less active coils due to a decrease in the spring constant, K. This is obvious for a constant material, wire diameter, and spring length. This is even true for springs with the same material, wire diameter, and wind, but with shorter overall length--IF they are displaced the same amount.

But when you are clipping a few coils and comparing different spring lengths with different effective displacements, you can't use that general rule that you stated as your "proof". Somebody just happened to guess right with how many active coils to clip off. If a couple more were clipped off I'm betting that you would see a drastic reduction in spring force potential.

I'm not argueing the result, I just disagree with your logic.

 

Back to the moddified carb questions...

So I just picked up a set of used '01 Raptor carbs for $50 and so for $250 the boring, port matching, and lightened butterflies will give 3hp? Is there anything else that I should look at doing? I don't want to ditch my airbox.

After these mods what is the performance comparison to FCRs? I'm not considering the FCRs, I'm just curious about the comparison.

Thanks

 

the thumb trottle tension is a result of butterflys, not the slide springs. Leave your springs alone or get Dynojet springs if you are uncertain. I think the rest has been covered.

 

Thanks airraptor, I am going to give it a try today.


This is the best thread I have read in months.[img]i/expressions/face-icon-small-smile.gif[/img]