Carb slide balance drilling?

[sailfish]

I thought that I'd break this out as a new topic to see if we'd get more responses. In another topic j98sprint asked:

On 2005-02-12 08:21, j98sprint wrote:
Could one of you fellow Sprinters enlighten me on this carb slide balance drilling mod? New one on me.

j98sprint

I too am interested in this. I looked on the Hinckley FAQ and they eluded that Dynojet kits have a drill for this mod. In the FAQ 4 cylinder carb mods, it states that the drill is a #40. but that is for the 1200 so it may be sized differently.

I've enjoyed the stock Sprint for almost 40,000 miles but I just can't leave it alone anymore! I have a 509 Speed Triple 3-1 header in a box on garage floor, I'm shopping for a Gixxer can on eBay and I know I'll have to open up the carbs to make it all work, might as well do thisl while I'm in there. I imagine pulling those carbs out and in is as close as I'll get to delivering a baby. Similarly, it probably gets easier the more you do it.

[TrumpetSprint]

This procedure was performed when I had some other work done on my carbs. I suspect the plugs are on only American Bikes. I also suspect it may be EPA related. Why else would there be a soft aluminum plug over an adjustment screw.

I did some searching on the web and found a reference to unplugging the idle mixture screw.

There was also another piece for replacing the idle mixture screw for a CVK on a Harley. It stated to remove the soft aluminum plug, remove and replace the idle mixture screw, seat it gently, and back off 1.5 turns. It also referenced EPA and state requirements.

Since the various Triumph chats mention 2.5 - 3.0 turns, I suspect it enrichens the idle mixture.

[TrumpetSprint]

Another link. It's for a Harley, but the Carb is a Keihin CV.
http://www.nightrider.com/biketech/hd_cv_mods.htm

[stevetoxic]

Hi Saltfish, I'm interested in your T509 header mod....I posted a question a few weeks back asking if any models had stainless pipework that would fit the trident (was thinking of Tiger pipes at the time as there was a set on ebay)
Is this a straight forward "bolt on fit" or do you need a degree in mechanical engineering ??
Thanks Steve

[trypcil]

I don't remember the size drill but I do remember when picking up my jet kit, the parts guy saying....." you'll loose some of your engine breaking, you realise "..... he was referring to a negative consequence of drilling the slides. Now the bummer is - I think he was right, however I've had flatslides since 97 and can't really say I remember, for sure. So that's my rotten egg, lobbed into the fray - as it were... but maybe someone more expert than I is able to explain what 'goes on' when you 'drill that hole' - it wasn't much bigger as I recall (hic!), perhaps a smidge or so. Personally I think the only way to put a jet kit in is have it done by 'dyno bloke'. And I say that because you need evidence that the jet kit really worked - a before and after. The seat of the pants meter isn't even analogue, and dog forgive that you ever show the readout to anyone, other than your proctologist! Plus with the dyno printouts, you can stare at them for hours, lots of uses infact. They've got stuff on them, data and things - it's interestin', plus you can write notes on the back, what you had for breakfast etc..how it drives .... "it's wicked man, it's wicked".....plus you can show your mates over a beer or something. :-D

[sailfish]

Steve,

Regarding the 509 Speed Triple header, here is what I know (I haven't tried it on the bike yet). I got the tip from a shop who had fitted one to a Sprint, so it actually will fit. You need the T509 Speed Triple header with the ROUND ports. The 955 stuff has oval ports. Holding it up under the bike it looks like a great fit. As it routes under the bike, it makes a nice little swoop around the oil filter cover and pops out on the right roughly where the stocker does. I have a suspicion that a Sprint ST can might work but there are none in Lincoln NE that I know of for me to borrow so I am looking at fitting a GSXR can (good volume, light, fairly cheap) and taking it to a muffler shop to get an intermediate pipe made. One down side is that with the stock left can gone the center stand has nothing to rest against so a bracket will need to be fabricated also.

This whole project is probably barely worth in performance gains but I like the 3 to 1 look, I want more sound, I'll hopefully drop 10 lbs off the back of the bike, and since my original header has a ding in it I figured why not?

[ This message was edited by: sailfish on 2005-02-13 11:23 ]

[j98sprint]

So, are we talking about the well known procedure of removing the EPA plugs and resetting the air mixture screws a couple turns out---or---actually drilling some sort of a hole in the carb slides for some performance gain?

I'm still not clear on this.

j98sprint

[sailfish]

J98Sprint,

I'm with you, really what is this? TrumpetSprint was referring to accessing the mixture screws but it appears that there is a slide hole enlargement that can be made to get the slides to respond faster. What I'd like to know is where are the holes and how big do you make them? Is it worth doing?

M

[TrumpetSprint]

OK guys, my mistake. When the drilling Slide Balance, I assumed (incorrectly) he was talking about the idle mixture screws.

I did some further research and found the following link. http://members.aol.com/roundr1/CVK40.html

It appears the slide balance hole links the venturi vacuum to the chamber above the slide.

"As you advance the throttle cable that's connected to the butterfly valve, the butterfly opens to allow more air through the venturi. This increases the vacuum effect that is transferred up through the vacuum drilling (the hole you bored out for the Dynojet kit), on the diaphragm valve slide), that leads to the TOP diaphragm chamber."

The #40 drill (0.098"), enlarged, would allow the vacuum to be transfered quicker, therefore allowing the slide to rise quicker, exposing more of the taper on the needle, thus more fuel, etc.

"The top chamber is separated from the BOTTOM chamber by the rubber diaphragm. The bottom chamber is open to atmospheric pressure from the airbox by the crescent shaped
casting on the top of the venturi. When the vacuum in the top chamber rises sufficiently, the constant ambient pressure
of the lower chamber, helps the diaphragm valve overcome the downward force of the diaphragm spring, and it rises from the venturi.

As the diaphragm valve is raised from the venturi depression (lowest pressure area), the needle is pulled further out of the needle jet, exposing a thinner portion of the needle taper which allows even more fuel to rise into the venturi to meet the increased engine demand."

Perhaps this will add some clarity.

The #40 drill should work the same on a 1200 Trophy (4 carbs, 4 295cc cyclinders) as on a Sprintetc (3 carbs, 3 295cc cyclinders) and from what I can pick up the relative tune on the two is compatitable.

[TrumpetSprint]

As a further comment.
Supposedly this mod will reduce engine braking. I suspect it has to do with the air returning back into the upper chamber causing a temporary low pressure (the orifice acting as an expansion valve) slowing the slide's return to the lower position.
Unfortunately, if you don't like the mod, you can't undo it. You can't undrill a hole.
Perhaps the owners who've installed dyno-jet kits can shed more light on its effects to engine braking.

trypcil's reference to installation by a dyno-bloke is valid. Part of the Dyno-Jet kits parts has to involve some trial & error and dyno testing to get the best performance. (The jets can't possibly cost that much $.)