Carb Spring Mod?

[zophar]

Ok. here's the Q.

The spring on top of the slide in the carb holds the slide down. The engine pulls vacuum to lift the slide. It has to fight the spring to raise though.

I've heard people say that longer springs helped there throttle response a ton.
I would think a softer spring or shorter spring would hep the slide lift faster therefore giving better response.

Anybody fool with this.

I tweaked my spring length and shortened it and seemed to help my throttle on the quick pop coming out of corners.
I'm gonna try it out on the track tonight and see what else happens.

[zophar]

Throttle response is very fast.
The slide comes up quicker. I was able to snap the throttle and keep up with my dad's 450R on the back stretch of the track wide open. I've also got a 13 tooth sprocket up front.

Between that, adjusting the needle and removing the box lid. I was sliding with the front wheels off the ground coming toward the double on the front stretch.

Something to think about if you don't have the extra funds to throw down on an aftermarket carb.

[zophar]

Once again I could keep up with the 450. I've got way faster response. If I am at 1/4 throttle and give it a quick blip to full rounding a curve it lofts the front wheels and launches.
Easily twice as fast as stock.

I only need 1/4 throttle to make it around the track, when I stick it on the way to the tabletop you can feel the bike launch foward. Nothing to be in 3rd or 4th gear and break loose on the way up the ramp.

It will out perform my friends 660 on accel out of the turns, where he used to gain on me.


Anybody else ever try it?

I see I've had some views, but no responses yet. come on guys.

[kfxguy2006]

Thats a stock carb?? Most of use ditch that POS and get an FCR. The throttle response is WAY better than stock.

[zookie400]

i have done it on a street bike to tone it down, but i didnt make the spring shorter......i found stiffer ones and put them in. the kid was having a hard time riding his new bike and keeping it on the ground.

you dont want to cut the spring, that will make it shorter but stiffer.

also you can try drilling out the hole that supplies vaccuum to the diaphram.

there is a problem that will arise however.....that carb isnt a pumper, so if the slide opens quickly, it will bog and die. thats why it opens as needed, not with your thumb.

get an fcr.

[zophar]

I plan on an aftermarket carb later.
But for a 2 minute 0$ trick it worked.

Think about the stiffer spring idea.
It makes it harder for the slide to come up. and doesn't allow full flow since the spring will be holding the slide down, into the opening of the carb.

With a shorter spring the empty spot disappeared while pinning the throttle fast.
Let the rpm's raise faster, and provided more airflow at WOT since the slide is out of the way.

I didn't take a lot of spring out, just enough to compensate for the slide hanging down.

The only difference that isn't an improvement, didn't hurt anything either.
Instead of dropping of the gas and the rpm's falling like a rock, it floats down slower, not slow enough to hurt, but slow enough not to drag down the quad into a curve.


Nothing to sneeze at from a stock carb.
It will keep up with, and pass occassionally, my dads honda 450r, which has an fcr on it.
So I'd say it's not too shabby for a mod on a mostly stock bike.

But I say thanks for the guys that have sent me messages saying they tried it and it worked.
Not everybody ,with this crap hole economy can lay down a lump of cash for an FCR.

[JETS_Z400]

I`ll give ya credit where it`s due...

#1. For coming up w/ that mod for the stock POS BSR36 CV carb. (I`d most likely do it to mine IF I was still runnin` it...but I`m not though).
#2. For apparently being a bit better rider than what your Dad is. (If you can beat him on an MX track w/ your mostly bone stock Z w/ those POS "pogo stick" `03/`04 front shocks...you`re takin` a HECKUVA beating in the process!!! ).

[zophar]

QUOTE

(If you can beat him on an MX track w/ your mostly bone stock Z w/ those POS "pogo stick" `03/`04 front shocks...you`re takin` a HECKUVA beating in the process!!! ).[/b]

Thanks for the credit on the mod.
What's a freak thing, is we swapped places between the 400 and 450 and still hung with each other.
Granted with more wheel time on the 450 I could probably handle it better next time.

[JETS_Z400]

No problem & your quite Welcome!!!

Yeah...if you get a little bit more used to that 450R of your Dad`s (& ya play w/ all of the shock`s adjustments & get `em all dialed in for ya...IF he doesn`t mind lettin` ya do that to it that is!!!) you`ll probably be able to start pullin` away from him when he`s ridin` your Z.
It very well could just be that BOTH of ya are just a little bit more comfortable on your Z though as opposed to on the 450R & therefor you both can ride it just a little bit harder & faster.
I know that I`m a little bit more comfortable & can ride harder/faster on some quads than I am/can on other quads!!!

[Joshz400_03]

Hey man, could you get some pics?...Thinking about trying this..what the heck it makes sence

EDIT: Is it the spring right under the black cap? How many coils did you cut off?

[JETS_Z400]

QUOTE (joshz400_03 @ Jun 25 2008, 10:01 PM)

Hey man, could you get some pics?...Thinking about trying this..what the heck it makes sence

EDIT: Is it the spring right under the black cap? How many coils did you cut off?[/b]

Yup...that`s the spring he`s referring to!!!

I agree...it DOES indeed make sense!!!

I don`t know how many coils he cut off of it though...but my guess would be not very many...something like maybe 1 full coil & then stretch it out some in order to get it back to the proper length that it needs to be. Just keep in mind...ya don`t want to make it TOO soft!!! (like he said...it`ll start causin` a hangin` throttle situation...so ya don`t wanna go TOO far on moddin` it!!!). I`d recommend doin` it in little increments at a time!!!
I was thinkin` about grabbin` my stocker & pullin` it apart & tinkerin` w/ it & seein` what I came up w/ on it though...just for somethin` to do to kill a lil bit of time.

[Joshz400_03]

I will try 1 coil..maybe do this today but its spose to be like 90* today and the garage will heat up pretty quick..

[Joshz400_03]

Ok, tried it..i dont know if its in my head but it felt like it would be more responsive down in the low rpm's. I cut about 1 coil off and then gave it a small stretch (not much) It kind of seemed to get rid of my real low end hesitation think its a small jetting issue.. there was no throttle hanging either

[JETS_Z400]

That`s a GOOD DEAL then!!! The throttle probably will actually be a bit more responsive now (& especially noticeable in the lower range of the spectrum) since the slide can start raising up easier now. It doesn`t sound like ya went TOO far overboard on it then either since ya aren`t experiencing any signs of a hanging throttle/idle.

[camaro1976]

QUOTE (JETS_Z400 @ Jun 27 2008, 01:33 AM)

That`s a GOOD DEAL then!!! The throttle probably will actually be a bit more responsive now (& especially noticeable in the lower range of the spectrum) since the slide can start raising up easier now. It doesn`t sound like ya went TOO far overboard on it then either since ya aren`t experiencing any signs of a hanging throttle/idle.[/b]

Paul your my hero.... I'm gonna see if that dillweed i bought my carb from put the softer spring in it and thats why i'm having so much problems with it. maybe i'll put the spring back in the throttle housing too.