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Drilling the slides.

Jeez! You guys are getting too scientifical for me.
I'm going out to play with the ZX now.:) New hugger to install and a couple other goodies!
 
Steve said:
On my carbs, that oval port is connected to the bottom side of the diaphragm. :shock:

The only way I can see vacuum getting to the top of the diaphragm is to go through the hole in the bottom of the slide. That is exposed to the faster-moving air in the venturi area of the carb, so it will have the lowest pressure. Most of the vacuum will be on the engine side of the throttle butterfly valves. About the only time the hole in the slides would see the same amount of vacuum would be during wide-open throttle, when there is no restriction caused by a partially-closed butterfly.

The vacuum seen by the slides is directly related to the amount of air passing through the carb, so it will lift accordingly. The amount of vacuum in the intake tubes (where you connect the gauges to sync the carbs) can change depending on engine speed at any given throttle opening.


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Click to expand...
So you think you need to drill the slides because there is less restriction of the air flow with the pods?
I see your theory on the faster moving air in the venturi finding it's way through the slide air port and to keep the air flowing with the oval air port at the rear of the carbs.
 
Actually, let me back up just a bit here. I had never thought of drilling the slides until I helped someone install a DynoJet kit, which suggested drilling the slides, but did not say why. I had never heard of drilling the slides, so it caught me by surprise.

Now, my (new-found) idea on why they need to be drilled at all:
Part of it might be due to less restriction at the air filter, but the larger hole in the slide will allow faster transfer of air pressure differences between the venturi area and the space above the diaphragm. A normal-sized hole will eventually equalize the pressures, but the larger hole will get the vacuum to the top of the diaphragm quicker, and will lift the slide sooner, making the mixture a bit richer, sooner.

Oooohh, too much thinking, and it's raining here, so I can't go for a ride. ](*,)


.
 
Yes, you are spot on. You're getting more air quicker so you also need more fuel quicker.

Dan :)
 
Sorry if this question is too specific on the more broad range thread...

Podsandwrap.jpg


I'm running my '83 GS650g with K&N Pods, a wrapped 4 into 1 exhaust. My main jet is 135 at the moment, and I'm still not running 100%. The Previous Owner said that he rejetted the bike, but I don't think he did it correctly, so I'm trying to run through it myself. I don't believe he drilled the slides, but I'm not sure.

Couple Questions: regarding the Mikuni bs32ss carbs.

What would be the stock hole size for this carb?

Why does the slide guide holder cover the air hole?

If I were to redrill this hole, how much larger should the hole be?

Would it be easier to just drill a new hold on the other side of the slide instead of redrilling the existing hole (this would make it easier to go back to stock later, by filling the new hole instead of filling and redrilling to stock size later)?

Carbslide_01

Carbslide_03

Mikuni bs32ss
Mikuni bs32ss
 
Wow, this was in informative carb thread!
I have some parts on the way from Chef, I bet I get good effect from replacing my one slide spring that is "sprung" and the one that is mismatched and smaller. Not to mention the diaphragm that has a tear.
 
Steve said:
Actually, let me back up just a bit here. I had never thought of drilling the slides until I helped someone install a DynoJet kit, which suggested drilling the slides, but did not say why. I had never heard of drilling the slides, so it caught me by surprise.

Now, my (new-found) idea on why they need to be drilled at all:
Part of it might be due to less restriction at the air filter, but the larger hole in the slide will allow faster transfer of air pressure differences between the venturi area and the space above the diaphragm. A normal-sized hole will eventually equalize the pressures, but the larger hole will get the vacuum to the top of the diaphragm quicker, and will lift the slide sooner, making the mixture a bit richer, sooner.

Oooohh, too much thinking, and it's raining here, so I can't go for a ride. ](*,)


.
Click to expand...
Yes. The reason for drilling the orifice to the diaphragm chamber is to improve throttle resoponse that MAY be lost when you install free flow filters on CV type carbs. Depending on your particular set up/bike, you may find no significant loss of throttle response and won't benefit from increasing the orifice diameter. Much more often than not it does benefit the throttle response, unless you screw the job up which happens too.
 
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