Don't know whats going on with yours. This is a very common mod with Hondas. Never heard of that problem.

 

Although in some cases it may be a bottom end throttle response improvement, overall shortning the slide spring is asking for trouble.

When you clip coils off a spring it does 2 things.

#1 It makes it shorter so the initial preload is less. Thus giving it a faster response to the initial vaccum change equaling quicker response at a low RPM throttle snap. This is good.

#2 A shorter spring is a stronger spring. Yes shortning it makes what is left stronger. That means after the initial easier than normal (due to less preload) travel it is going to be harder to compress throughout the rest of the slide piston stroke. This means is is going to be opening too slow in the later stages creating decreased performance. This is bad.

A CV carb is designed to only open the throttle as fast as the engine will accept it, to keep it from falling on its face when the throttle is snapped open. That is why the vaccum diaphram and piston is there. The factory sets the spring rates conservatly(sp?) to make sure there is not a lean bog in throttle response.

There are 2 ways to correctly cure this.
The most popular is the Dynojet spring. Its just not just shorter, but weaker overall. This give less preload for quick response and less tension so the slide opens a little quicker throughout the entire stroke.
The poor mans way is to leave the spring alone and drill the vaccum hole in the slide. This gives the same effect as a weaker spring because you have more airflow (vaccum) reaching the diaphram thus making it respond quicker. Some say to drill to 1/8" but in my experence 7/64" is better. Too large a hole will cause the slide to "dance" rapidly up and down which makes for an erratic running engine.
DO NOT drill the slide if you are running a weaker Dynojet spring or have already clipped the stock spring shorter.

 

how's that friend? how does the rate change by cutting the spring? that's what you mean, right?

I haven't felt the need for the mod so I can't say if these springs are, but I think the spring would have to be wound progressively for that to be true. Right?

dirtbiker, at 4.5k' I would assume your jets and/or airbox need adjustments to keep up

 

I dont know the exact science of it, I just know its true.
I sure if you done an internet search you would find the answer.
I think it has something to do with less area to bend, but I'm not sure.

 

I'd check that

 

http://www.off-road.com/dirtbike/tech/2002spring/

For anyone that has doubts (propnut) copy, paste, and enjoy.
This is a good article on the hows and whys of shortning a spring makes it stronger
I feel sure there are many more articles on the same subject.

 

According to this proceedure they use to figure the spring rate, wouldn't there have to be a spacer added to the spring replacing the area clipped out, within the diaphram chamber, in order for it to retain the intended stiffness gain calculated per front fork tube method ? Since the distance in the diaphram is still the same from top cover to spring seat in the slide, with no spacer, the coils actually uncoil with this soft of a spring ( within the venturi distance ) changing the coil wind number, and actually making the spring rate softer per wire diameter and beginning compressed distance. Figured the way the front fork was with a spacer, the spring coils were actually retained with the spacer or the fork tube would colapse, changeing the distance and preloaded pressure would be weaker ( without a spacer ). In the carb venturi this distance never shortens as it is a fixed measurement extended, and no preload force needed to retain like a desired ride height. Like I said, the spring preload is less with it shortened within this distance (of the venturi) and no spacer to bring the tension back up to calculated strength after being shortened. So the shortened spring is actually softer within the venturi when clipped because the spring in question is soo much longer than the distance it needs to fill in the diaphram chamber, when shortened there is less tention to begin with. The springs they are working with have adjustable distance or to make their figures work a spacer is added to make up for a shorter spring. The venturi spring is longer than the fixxed measured area from the get-go.
What they are missing in the arcticle you posted is, the front fork distance and spring tension without the spacer installed ( the fixed rate distance is changed ). And on the rear spring the fixed rate preload is adjusted by its threaded collar making up a shorter distance to gain their desired tension per mathmatical method of figuring as the preload is gained back by adjusting the preload. ( Confused yet ? )
Since the distance in the venturi area of a carb is fixed extended and the spring is longer than this distance, you can install a stiffer spring rated at an inch, installed into a two inch area and the preload is less (Softer). That is why they require the spacer with in the fork.
A Spring will get softer at the beginning preload when streatched or lenghthened with less coils, the same way as how they are preloading a shortened spring in a shorter distance.
Reguardless, once compressed after benig shortened to the springs wanted rating (or desired rating as they explained) per inch, yes you are correct.
The initial preload in the venturi is softer at its beginning loaded distance though, giving snappy throttle response, and as it compresses it will get stiffer than origionally intended per coils cut.

This is why when you purchase an aftermarket venturi diaphram spring from a manufacturer, it will be progressive to make up for this mathmatical equasion, they stated is complex, within the suspention spring arcticle you linked us to.

----- Gregg -----

 

so friend, how many active coils are they cutting off their spring and why doesn't this work for the Rincon and others again?

 

Thats what I was saying in my origional post.
The softer initial preload makes for more snappy throttle response as wanted.
But the stiffer rate makes for slower opening in the later stages which is bad.
So when you clip the spring, you improve one area while harming another.
Thats why it is better to go a different route. So there is no tradeoff and you can improve everywhere.

 

So Rinman and Foreman Dan, have you experienced an adverse effect on the near wide open throttle response or max power by doing the modification, as our friend theorizes?