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SuzukiSavage.com
/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> Bigger vacuum port on Stock CV Carb??? /cgi-bin/YaBB.pl?num=1407855470 Message started by DaThump on 08/12/14 at 07:57:50 |
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Title: Bigger vacuum port on Stock CV Carb??? Post by DaThump on 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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Title: Re: Bigger vacuum port on Stock CV Carb??? Post by Dave 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 |
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Title: Re: Bigger vacuum port on Stock CV Carb??? Post by verslagen1 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. |
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Title: Re: Bigger vacuum port on Stock CV Carb??? Post by Serowbot 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.... |
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Title: Re: Bigger vacuum port on Stock CV Carb??? Post by DaThump on 08/12/14 at 10:41:20 102B2631202C37312A222F30430 wrote:
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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Title: Re: Bigger vacuum port on Stock CV Carb??? Post by DaThump on 08/12/14 at 10:47:48 140710110E0305070C53620 wrote:
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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Title: Re: Bigger vacuum port on Stock CV Carb??? Post by DaThump on 08/12/14 at 10:51:31 2731263B23363B20540 wrote:
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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Title: Re: Bigger vacuum port on Stock CV Carb??? Post by DaThump on 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-throttle-slide-cv-carb-9399/ 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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Title: Re: Bigger vacuum port on Stock CV Carb??? Post by Serowbot on 08/12/14 at 12:44:14 3C2420570 wrote:
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 [/quote] 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.. :-?... the point is, you could play around with that without boogerin' yer' carb permanently... ;)... 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... ;D... |
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Title: Re: Bigger vacuum port on Stock CV Carb??? Post by Dave on 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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Title: Re: Bigger vacuum port on Stock CV Carb??? Post by engineer 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. |
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Title: Re: Bigger vacuum port on Stock CV Carb??? Post by Serowbot on 08/13/14 at 06:53:01 74767D767F767A60130 wrote:
This is my thinking... It's there to prevent pogo sticking yer' slide on every engine pulse... ;)... |
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Title: Re: Bigger vacuum port on Stock CV Carb??? Post by Dave on 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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Title: Re: Bigger vacuum port on Stock CV Carb??? Post by DaThump on 08/13/14 at 17:09:15 6D6F646F666F63790A0 wrote:
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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Title: Re: Bigger vacuum port on Stock CV Carb??? Post by DaThump on 08/13/14 at 17:23:02 4B5D4A574F5A574C380 wrote:
Jes' guessin' here.. :-?... the point is, you could play around with that without boogerin' yer' carb permanently... ;)... 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... ;D...[/quote] After looking into it Those both seem to be pilot circuit airjets http://www.suzukipartshouse.com/oemparts/a/suz/506b36c3f870022ba8af9e73/carburetor 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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Title: Re: Bigger vacuum port on Stock CV Carb??? Post by DaThump on 08/13/14 at 17:39:02 6B505D4A5B574C4A5159544B380 wrote:
eesh, that's not a good thought. I'm almost positive it was your post that spurred this idea... I read awhile back (I'm a long time lurker) about not putting in a UFO in a VM34 carb because nobody seems to be able to get the jetting just right at low RPM. So I started looking for alternatives and stumbled across that how to article So if this goes terribly wrong I should blame you...right? :) |
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Title: Re: Bigger vacuum port on Stock CV Carb??? Post by DaThump on 08/13/14 at 17:49:29 Found another article http://bonniemods.info/Tweaks/AirSlide |
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Title: Re: Bigger vacuum port on Stock CV Carb??? Post by Serowbot on 08/13/14 at 18:16:33 50484C3B0 wrote:
I think Keef's a bit of a loon... :-?... Have fun wreckin' yer' carb... :-/... |
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Title: Re: Bigger vacuum port on Stock CV Carb??? Post by DaThump on 08/29/14 at 12:52:49 Update. I got lazy and didn't want to rejet carb from factory specs, install carb, test jets/carb, uninstall carb, drill vacuum ports, reinstall. So I rejetted and did the vacuum ports at same time. I rejetted from factory 3mm white washer on pilot needle to 1.5mm (three washers from lancer's carb jet kit) and from a 145 main to a 152.5 main. It's still a little lean on pilot needle (factory settings are ridiculous). Only change was switched from factory air filter to "HiFlo" one. The original vacuum ports are approx 3/32 (a very little bit bigger). With the carb cleaned, and off bike, I blew into air port that pushes diaphragm to move the slide up/open. I did this over twenty times to chk its movement. Took carb apart to start the drilling...the only bigger drill bits I had were 7/64 and 1/8. I did 7/64 with a little bit of rounding motion as I drilled to open up the ports more. I also changed the two screws that hold the pilot needle on the slide (used allen cap head M3x6). I'm sure these added a very small weight gain. By my rough calculations each vacuum port area was increased 33% to 50% more. So I almost doubled total area. Had to use this site http://www.mathsisfun.com/geometry/circle-area.html cause my 'circle math' is rusty. I put the carb back together. What a difference when I blew into air port. The slide moved noticeable faster but still smooth. Way faster. The throttle feels more responsive...how much is from porting or rejetting is impossible to tell. When I open throttle wide open the initial hesitation is decreased and acceleration seems a lot more connected to my wrist. Doesn't have the feel of a pumper carb but feels a lot less like the acceleration from CVT. No real difference when I decelerate, but I never payed attention before either. It's been a few hundred miles, so far so good. I'm not worried about any long term damage. The slides plastic is stout and has to deal with constant engine vibes. |
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