Carb modification for CV carbs

[Guest]

Hey All,

as I was installing my Jet Kit from "6 sigma" there was an optional step of cutting "one turn" off of the spring that the needle sits on (about 1/8th on an inch). They say this will reduce the spring tension and at 2200 RPM and higher will result in nearly instant power delivery when opened to WOT. Below that rev level it will be much softer power delivery.

I went with it seeing that I have 4 extra springs at stock length. I do not have the bike put back together yet, need a few final adjustments. But when I do I will let you know the result.

I would assume that this would work for all CV carbs. use the base line "one turn" cut to start with and go further if you want more response.

Has any one done this or heard about this modification?

[Steve]

If that is the spring that holds the needle in place, there should be enough tension to prevent any movement of the spring.
Reducing tension won't matter, as long as the spring is still held in place. The problem with cutting that spring is that, if you cut too much, the spring will not be held in the proper place and your needle jetting will be ... well ... variable. Not sure that it would be all that desirable.

You sure you are cutting the right spring?

Seems to me that if you were to cut the spring that pushes the slide down (the one above the diaphragm), you would lessen some tension and maybe increase some response.

.

[Danaconda7]

Yes but I will double check. with the new jetting it required more spacers placed on the needle so that took up the space from the lost one turn. but I will check the tension and make sure it is not too loose.

[1980GS1000E]

The needles will only move with respect to the slide if they are loose. Any spring compression on them at all will hold them in place as there is no force acting upwards on the needle. However, I am in agreement with Steve about the slide return spring. Less spring force on the slide could result in quicker response. You don't want the spring so weak that the slide doesn't return, though. I don't think that cutting coils off the slide spring would be as effective as replacing the spring with a lighter one.

[tkent02]

Most people enlarge the hole in the slide for quicker response, have you looked into this?

[Steve]

Most people enlarge the hole in the slide for quicker response, have you looked into this?

That is the solution with the DynoJet kits, they even include the drill bit.

.

[1980GS1000E]

Sounds like it might be worth a try. What size bit?

[tkent02]

I'd go with the smallest one that's bigger than the hole now. Drill, test. Drill again, test again.

When you get too big, make the hole smaller again and call it good.

I think I read the one Dynajet sends is 1/8 inch, but I'm not sure.

[derwood]

My 2 cents
I too figure they mean the slide return spring. The result would be similar to drilling the slide, making the slide rise quicker.
I don't agree that it would improve throttle response on all cv carbs.
I don't think you can change only one thing and expect a performance increase. (in a carburetor) -more likely a decrease.

the carburetor is tuned to coordinate fuel (gas) delivery with airflow. If all you do is clip the springs or drill the slides the carb slides rise too quickly.The midrange will lean out as the air flow will get ahead of the fuel flow. ( It will catch up )

My 1150 slides are not drilled, nor are the return springs shortened. They pilot, main jets and jet needles have been changed.
The Hawk slides are drilled, (Dyno jet kit -1/8 drill bit) stock spring length.

[Danaconda7]

I hear what you are all saying about which spring they were talking about. I will reread and photograph the instructions tonight and post tomorrow. I will also call them and figure out what their goal is with this spring cut.

As for drilling the slides, I have already done this as part of the re-jetting. 6 Sigma supplied me with a 5/32 drill bit for the slides and mixture screw caps. As well as a screw to remove the caps.

I will let you all know what they say and what I do.

[John Kat]

Don't forget that when you cut a spring shorter, it raises the force required to squeeze it not the opposite

[Danaconda7]

Well I feel pretty foolish. Not sure how i misread the instructions but you guys were right. They were talking about the Slide spring. Sorry everybody, still learning.

[salty_monk]

Sounds like it might be worth a try. What size bit?

Think it's about 4mm...

[gearhead13]

The DJ kits I have had (gs 750 and 1100) had different size bits for them. Usually number drills, I believe their pdf files list the number size on them.
You have to make sure to use the proper drill bit, not the plug drill bit.

http://www.dynojet.com/pdf/3133.pdf

http://www.dynojet.com/pdf/3315.pdf

[Danaconda7]

thanks for the advise but they sent only one bit. So I used the one provided as instructed. Carbs are all done and will fire this weekend. I will let you know if what I did messed things up.