SuzukiSavage.com - Bigger vacuum port on Stock CV Carb???

DaThump YaBB Newbies Offline SuzukiSavage.com Rocks! Posts: 20	Bigger vacuum port on Stock CV Carb??? 08/12/14 at 07:57:50 What I really want is the responsiveness of a VM roundslide (Lancer's kit) BUT that's a few mods out Has anybody drilled a bigger hole for the vacuum port in the stock carb slide? How did it work out? I'll start to :'( if I ruin my slide (I'm not ashamed to admit it btw I've searched the forum extensively for this topic
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Re: Bigger vacuum port on Stock CV Carb???
Reply #1 - 08/12/14 at 08:16:50

I don't know what you intend to accomplish. The carb only lifts the slide in response to the engine vacuum...if the engine vacuum decreases in the venturi the slide drops, if the vacuum in the venturi increases the slide is raised. The port size most likely is not a restriction in the operation of the diaphragm and slide. The CV carb is not a performance carb....it is made to allow the engine to operate smoothly, even if you get too aggressive and crack the throttle open very quickly.

If you fuss with the spring pressure and allow the venturi to rise easier, you may cause the vacuum in the venturi to decrease, and then you will have to reject to account for the fact that less fuel will be pulled through the jets.

The VM Roundslide carb will not do much alone. With other engine improvements like a Wiseco, cam, air filter, head and exhaust changes, then you can get the 30 hp to increase by a few HP. The engine becomes more responsive.....but it never gets to be "fast".

Dave

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verslagen1 YaBB Moderator ModSquad Offline Where there's a will, I want to be in it. Posts: 28886 L.A. California Gender:	Re: Bigger vacuum port on Stock CV Carb??? Reply #2 - 08/12/14 at 08:39:24 No ones done it cause it's insane. buy yourself a vm carb, cause if you make that mod you'll be walking instead.
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Serowbot YaBB Moderator ModSquad Offline OK.... so what's the speed of dark? Posts: 28660 Tucson Az Gender:	Re: Bigger vacuum port on Stock CV Carb??? Reply #3 - 08/12/14 at 08:50:22 There is an airjet up in the top above the slide diaphragm, that might initiate the response you're looking for....
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Re: Bigger vacuum port on Stock CV Carb???
Reply #4 - 08/12/14 at 10:41:20

Dave wrote on 08/12/14 at 08:16:50:

I don't know what you intend to accomplish. The carb only lifts the slide in response to the engine vacuum...if the engine vacuum decreases in the venturi the slide drops, if the vacuum in the venturi increases the slide is raised. The port size most likely is not a restriction in the operation of the diaphragm and slide. The CV carb is not a performance carb....it is made to allow the engine to operate smoothly, even if you get too aggressive and crack the throttle open very quickly.

If you fuss with the spring pressure and allow the venturi to rise easier, you may cause the vacuum in the venturi to decrease, and then you will have to reject to account for the fact that less fuel will be pulled through the jets.

The VM Roundslide carb will not do much alone. With other engine improvements like a Wiseco, cam, air filter, head and exhaust changes, then you can get the 30 hp to increase by a few HP. The engine becomes more responsive.....but it never gets to be "fast".

Dave

I'm trying to get the best of both worlds between the VM and the CV...I got the idea from this page http://www.nightrider.com/biketech/hd_cv_mods.htm That and when I got the bike the throttle response seemed sluggish. When I went to change the washers on the pilot needle, it looked like cover plate was on upside down and was slightly blocking the two vacuum ports. When I put it back on the vacuum ports weren't blocked.
The thought was/is if I jet it correctly, at least not factory lean, then have the slide more responsive to engine vacuum but not to become so lean as to significantly bog down. (I'm assuming that's what happens with the VM when cracked open)

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DaThump YaBB Newbies Offline SuzukiSavage.com Rocks! Posts: 20	Re: Bigger vacuum port on Stock CV Carb??? Reply #5 - 08/12/14 at 10:47:48 verslagen1 wrote on 08/12/14 at 08:39:24: No ones done it cause it's insane. buy yourself a vm carb, cause if you make that mod you'll be walking instead. It's not that insane...maybe a little 'out there' I stole the idea from the harley guys any (yes, yes, I know. that's my problem to begin with)
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Re: Bigger vacuum port on Stock CV Carb???
Reply #6 - 08/12/14 at 10:51:31

Serowbot wrote on 08/12/14 at 08:50:22:

There is an airjet up in the top above the slide diaphragm, that might initiate the response you're looking for....

That's a fantastic idea. I soulda coulda woulda thought of that. Hmm, I'd assume a bigger airjet would, if it works at all, push the slide up faster.

thanks

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Re: Bigger vacuum port on Stock CV Carb???
Reply #7 - 08/12/14 at 11:40:56

JIC anybody else is following this thread. I found a article http://www.indiancarsbikes.in/automotive-technology/crisp-punch-ported-thrott...
I think this is a heck of a lot better than messing with the slinky like spring for the slide. I just did a small air filter mod, so I need to establish a new baseline with jetting before I try this. Looks promising tho. I'll definitely follow a "less is more" attitude when drilling

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Re: Bigger vacuum port on Stock CV Carb???
Reply #8 - 08/12/14 at 12:44:14

DaThump wrote on 08/12/14 at 10:51:31:

Serowbot wrote on 08/12/14 at 08:50:22:

There is an airjet up in the top above the slide diaphragm, that might initiate the response you're looking for....

That's a fantastic idea. I soulda coulda woulda thought of that. Hmm, I'd assume a bigger airjet would, if it works at all, push the slide up faster.

thanks

Not certain how that jet works,.. but I imagine it's there to allow the diaphragm to move up and down with only spring resistance and not the vacuum resistance that would be created if the space above the diaphragm was air tight... If so,.. a bigger jet would allow the spring to move faster...
(probably vents to a neutral air source)... (it can't run to vacuum, or it would be pulling up when vacuum is high, and adding fuel when you let off the gas)...

Jes' guessin' here.. Huh

... the point is, you could play around with that without boogerin' yer' carb permanently...
Wink

...
If I'm wrong,.. and it runs to engine vacuum... a bigger jet will create more resistance and slow the slide... making you leaner at every setting except WFO......

I just don't mess with it... Grin

...

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Dave YaBB Moderator ModSquad Offline SuzukiSavage.com Rocks! Posts: 18099 Camp Springs, Kentucky Gender:	Re: Bigger vacuum port on Stock CV Carb??? Reply #9 - 08/12/14 at 13:36:23 Well if you wanna' experiment.....take baby steps with the drill. As the article stated....2 times the diameter results in 4 times the area! And you most certainly don't want that slide moving 4 times the current speed. Dave
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Re: Bigger vacuum port on Stock CV Carb???
Reply #10 - 08/13/14 at 06:41:20

This is an interesting thread and the Indian article claims to report actual results. I have to assume that Mikuni knows a great deal about carburetors and wants people to be satisfied with their product. They must have had some reason for selecting the size hole they made. The only reason why they might have deliberately selected a size that slows throttle response would be for environmental compliance or fuel economy. Or possibly they wanted to filter out the pressure pulses that come from the action of the valves and intake strokes. Maybe those pulses cause some fluttering and wear out some of the components.

Anyway this is an interesting concept and if you drill it out I would certainly like to know the results.

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Re: Bigger vacuum port on Stock CV Carb???
Reply #11 - 08/13/14 at 06:53:01

engineer wrote on 08/13/14 at 06:41:20:

... Or possibly they wanted to filter out the pressure pulses that come from the action of the valves and intake strokes. Maybe those pulses cause some fluttering and wear out some of the components.

This is my thinking...
It's there to prevent pogo sticking yer' slide on every engine pulse... Wink

...

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Re: Bigger vacuum port on Stock CV Carb???
Reply #12 - 08/13/14 at 06:58:33

On early British cars, the CV carbs has a little piston and oil filled cylinder that stops the carb slide from bouncing up and down. It is a little shock absorber for the carb slide.

If the slide bounces up and down.....Wonder what that does to the fuel flow when the needle jet is bouncing in and out of the whole (jet needle)?

Dave

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Re: Bigger vacuum port on Stock CV Carb???
Reply #13 - 08/13/14 at 17:09:15

engineer wrote on 08/13/14 at 06:41:20:

This is an interesting thread and the Indian article claims to report actual results. I have to assume that Mikuni knows a great deal about carburetors and wants people to be satisfied with their product. They must have had some reason for selecting the size hole they made. The only reason why they might have deliberately selected a size that slows throttle response would be for environmental compliance or fuel economy. Or possibly they wanted to filter out the pressure pulses that come from the action of the valves and intake strokes. Maybe those pulses cause some fluttering and wear out some of the components.

Anyway this is an interesting concept and if you drill it out I would certainly like to know the results.

Not to discount the mikuni master minds, cause I'm sure they have the top echelon of engineers for their products.. but so does Suzuki, YET we still get a not so different 5th from 4th gear, a cam chain tensioner time bomb, a sliding seat, and a front brake that could have came off a 50cc scooter. It's still hard not to totally dig the thumper tho.

The power/pressure pulse idea seems like it has lots of merit but I'd be willing to bet the only reason the vacuum ports are that size is to make sure the rider did lean it (to a stall???) when they wot

I won't be able to get around to opening up the ports till a couple of weeks but I'll definitely report back...
I figure if I screw it up (or it doesn't work out well) i can buy a new slide washer and epoxy then redrill to original size. I'm thinking about just getting a washer to have on hand JIC

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Re: Bigger vacuum port on Stock CV Carb???
Reply #14 - 08/13/14 at 17:23:02

[quote author=4B5D4A574F5A574C380 link=1407855470/0#8 date=1407872654]DaThump wrote on 08/12/14 at 10:51:31:

Serowbot wrote on 08/12/14 at 08:50:22:

There is an airjet up in the top above the slide diaphragm, that might initiate the response you're looking for....

.

Jes' guessin' here.. Huh

... the point is, you could play around with that without boogerin' yer' carb permanently...
Wink

...
If I'm wrong,.. and it runs to engine vacuum... a bigger jet will create more resistance and slow the slide... making you leaner at every setting except WFO......

I just don't mess with it... Grin

...

After looking into it
Those both seem to be pilot circuit airjets http://www.suzukipartshouse.com/oemparts/a/suz/506b36c3f870022ba8af9e73/carbu...
I'd assume that they would have little to no effect on slide just cause they're so small compared to the air port that pushes diaphragm up.

I really really like the idea of not having to "boogerin' yer' carb permanently..." tho

maybe if this works out I can make it to the esteemed Tech how to section...never know

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