DIY carb sych connection

[LC Cnd]

Considering on building a carb sync (attach vid) for the 4L0. Question is attachment location to obtain an accurate meter reading - balance pipe tube openings? I've done the popsicle stick method due to clouded carb site glass(s). Using DIY sync'ing bottles appears less wear and tear method on the boots. I'm considering using two stroke oil as the leveling fluid.
https://youtu.be/7D_f05_a74Y

[MK]

For the RD's measuring the intake air pressure is not the best tool.
The reason is that this pressure is very small at idle.
A four-stroke has around 30-60 kPa (0.3-0.6 bar) at idle, the RD has around 95 kPa.
The WOT values are around 100kPa for both engines.

So the difference between left/right resulting from mismatched valve/slide position will be much higher in a fourstroke.
On the RD it'll may be only as low as 1 or 2 kPa.
And the second thing is the assumption that both cylinders produce the same vaccuum at the same "inputs".

Nevertheless: Measuring will result in a significant difference in water level in the bottles as 1 kPa equals 100mm water level.


I prefer looking into the carb belly from behind and adjust the cables to have both slides vanishing at the top edges simultaneously. That's an accuracy of a few 1/10 of a mm.
Even the butterfly valves of my EFI bike were just optically aligned and measured EGT & AFRs proved the method to be sufficient.

[LC Cnd]

Well Martin, your thoughts of manually sync'ing VM's cooberate what AU mikuni store advise on the subject. (https://youtu.be/9L6b8ji-SIE). Still curious on your thoughts on the function of the carb balance tube carb and why it creates a balance. Checked Gordon Jennings tuners handbook, for possible comment on the balance tube; didn't come across anything.

[kpke]

Interesting home made tool there. I recently sold one of the old school 4 up tools, the one that uses mercury, new in box. The dude said he had been looking forever for one of these because the new non-mercury one he bought sucked.

I use one of these on the 500 and it makes a huge difference synching the 4 carbs on that bike. Just did it a month ago after going through all 4 carbs "fixing" a leaking carb problem. I've never felt the need on any of the 350's though.

[MK]

The carb balance tube creates a "balance" because it connects left/right intake areas.
Yamaha introduced that to enhance low range performance of engines with small carbs.

It affects the carburetion in the lean way (i.e. tube mounted = richer idle jet required, tube holes blanked out = leaner idle jet required.)

The last device shown measures air flow and is certainly better suited for twostrokes than a pressure based device.

[LC Cnd]

Discussed this topic with Hondaror/Rory couple year's ago. Our discussion convinced me to purchase a vacuum gauge call a uni-sync (pic below). The issue with using it was is to wide for fitment between the airbox and each carb. So went with the popsicle stick for the time being instead of remove back wheel/uni-syn. Learned the pictured a/n'd gauge, which I've seen used on youtube vids when tuning banchees, works well but like the uni-syn. Both vacuum gauges are a bit of work compared to the cheaper sticks. Enough pontificating on my part. I'm going to have a couple of Corona's or whatever I can find in the recycle bin to build it; then compare it to the uni-sync and sticks after I go for a ride first. May just end up with the stick again - I'm ok with that.

Interesting vid comparing fluid vs vacuum M/C carb syn'ing. Fluid won out but on a 4 stroke engine starting at 7:00.
https://youtu.be/Ne3qqfW_dXA

Carb vacuum type sync banchee starts at 2:40. Works well.
https://youtu.be/hZ6EeABS3gk

[Evans Ward]

I use the same one that Ken uses and love it! I did have to custom make an adapter to reach the center carb for my vintage Triple motorcycles.

[Bare]

Those old Unisyn things were manufactured for roughly balancing the SU type Carbs on English Cars ie; Any that had twin (or More SUs .
As they went out of synch almost monthly. Small useless factiod is all.

[LC Cnd]

So Bare, it would work on a Jensen Interceptor 3 (was looking at one yesterday) and not on 4L0. What the alternative carb balancing tool recommended available say at Princess Auto or Cnd Tire etc for the VM26's?

[RC30Tech]

I just use a popsicle sticks to sync the sliders. Fast, simple and free.

[Bare]

So Bare, it would work on a Jensen Interceptor 3 (was looking at one yesterday) and not on 4L0. What the alternative carb balancing tool recommended available say at Princess Auto or Cnd Tire etc for the VM26's?

Huh? Owned a III in '78 Mine had a 383 lump and associated 4 barrel .
Seriously unlikely a Unisyn would even fit on, let alone work