XJ900 31A BS35 Mikuni Vacuum Slide (piston) vacuum hole size?

I Searched and searched but...

My slide vacuum holes have been drilled out to 3.5mm(ish, it might be imperial), I'm looking for the original size of the vacuum hole in the slide for the Mikuni BS35.

Thanks in advance.

 

Found an undrilled slide.
3/32" barely squeezes in and 2.5mm is too large.

 

Now you just need to drill 3 more slides smaller
You could epoxy them then drill to any size.
Why do you want to go to the OEM hole?
I’ve drilled out a few banks with understanding it just quickens the slide action.

 

Just did the 58l pistons in 31a cylinders and have a stumble at low end now.
Drop the needles and it's gone but the mid to high range is teeth grinding, whereas it is good at original position.
Epoxy is done. Waiting...

 

Indeed it does quicken the slide action, but this reduces the snap enrichment fuelling, which usually gives you a weak stumble, especially if you overdo it.

 

I figure I have full compression now so the flow is greater through the venturi. Previous I was down to 90 on the best cylinder and the drill out worked a charm.
Never satisfied obviously.

 

How does compression change the flow through the venturi then?
Answer is, it doesn't. Flow through the venturi is a product of cylinder volume, piston velocity, cylinder head efficiency, and the big one, how much the throttle is open.

 

Good point. Something is different though. So going back to standard.

 

That fixed it. Stumble gone top end still there.

 

Good the stumble has gone, but did you mistype the earlier post - saying you dropped the needles? Surely you raised them to mask a weak spot on acceleration?

 

No it was correct. Needles rising too fast. The opposite of the normal fault.

 

I did a video a few years back of the slide action in my HSC32's by mounting a small cube camera inside the airbox and riding hard. Gives a very good perspective on the life of a carbonator. Turn up the volume and enjoy the 10,000 RPM hits as I used a pro stereo mic and BetacamSP recorder for all this. Did burn up my clutch doing this... it wasn't happy.

When you're watching pay close attention to the slight haze that appears, this is the "spitback" or reversion of the air/fuel and the what I believe makes the pods a liability in that this is lost to the outside instead of being trapped in the resonant cavity of the OE airbox.

 

Note also the slight vac piston "bounce" that occurs at steady rpm's......I don't know if this is a unique feature of CV carbs, but they all do it, there's a couple of other videos (1100's) that people have made with this same viewpoint and it's present in all of them.

Very cool video.

 

Good vid. I did one of my vmax slides a few years ago,will have to dig it out. One thing that's easy to see is how much running is done on the idle jet.

 

If you watch the video carefully at around 0:55 and look down at the bottom of the slider right at the needle you can see just a smidge of fuel being pulled up from the jet as I lightly accelerate, this goes to about 1:07 and happens again at about 1:12 going until I pull the throttle open which the slider starts moving. It's this what I call "transition" fuel that makes the float settings so important. Without this little sip of fuel before the sliders wake up the motor goes lean and if the floats are too high fuel constantly runs out of the floor jet at idle making the screw settings impossible.

I now have a smaller camera that will allow more coverage of the floor area of the carb throat to get a better view of the jet & needle interaction during piston lift. Once the weather warms I will do another video to highlight this and possibly the reversion spitback into the resonant chamber itself during that critical 4500 to 6500 RPM bog. When I say warmer I mean above 50F as it's -12F here right now.

 

Good Lord, fly south for the winter!

 

I wish it were that easy @chacal.