34mm Carb holders w/vacuum plug for a mikuni upgrade1980 KZ1000 B4 LTD

The problem with vacuum syncing slides and butterflies is as the engine and carbs age, the vacuum produced by each cylinder/carb differs. This results in slides and butterflies set inconsistently - and while you may get a smoother idle, the mid-range throttle response is off - and that is where you ride.

It is better to make sure the slides are mechanically synced - on the work bench - and then never use vacuum sync tools to change them.

I do use vacuum sync to help set idle with the fuel or air screws, but I don't change slide or butterfly settings based on the vacuum readings.

These are what i made up for my XS650 as they don't make them with stubbs anymore.

Jeff.Saunders wrote: The problem with vacuum syncing slides and butterflies is as the engine and carbs age, the vacuum produced by each cylinder/carb differs. This results in slides and butterflies set inconsistently - and while you may get a smoother idle, the mid-range throttle response is off - and that is where you ride.

It is better to make sure the slides are mechanically synced - on the work bench - and then never use vacuum sync tools to change them.


I do use vacuum sync to help set idle with the fuel or air screws, but I don't change slide or butterfly settings based on the vacuum readings.

Interesting. If an engine has different vacuum readings at idle, do they equalize as rpm increase? If not, then shouldnt we tune each carb to its own particular cylinder's needs? Would it be better to change jets and adjust needles rather than have individual slide/butterfly settings?

Jeff.Saunders wrote: The problem with vacuum syncing slides and butterflies is as the engine and carbs age, the vacuum produced by each cylinder/carb differs. This results in slides and butterflies set inconsistently - and while you may get a smoother idle, the mid-range throttle response is off - and that is where you ride.

It is better to make sure the slides are mechanically synced - on the work bench - and then never use vacuum sync tools to change them.

I do use vacuum sync to help set idle with the fuel or air screws, but I don't change slide or butterfly settings based on the vacuum readings.

I suppose I will have to politely agree to disagree with some of that and i don't want to get into a prolonged debate as I know where you're coming from with worn out carbs but Vac syncing is to ensure that each cylinder is pulling the same work/air volume as it's neighbours regardless of slide height etc and should be done as a base line for any other carb adjustments.
Any other running and fuelling issues after that are down to carb settings and diaphragm wear on CV's which really needs addressing individually.

If cylinder compression/efficiency was all equal I would agree, but there have been many times when I attempted vacuum sync carbs, then when I pulled the carbs off the bike, the slides are all uneven.

So on a newly built motor, I would agree with you, but on an older engine the vacuum results can be all over the place.

This is where you have to consider what is going on with an older bike. If you have a cylinder down on compression,, or a carb that is leaking a little extra air past linkage seals, that carb will not be sucking fuel in at the same rate as other carbs.

So what do you want to achieve? A perfect idle, or the bike performing the best in the mid-range? It is usually a compromise.

With mechanical slide carbs, you absolutely want the slides to rise and fall perfectly in unison - that way the fuel flowing past the needle / needle jet should be optimized for the mid-range - and that is where you ride.

Vacuum carbs work a little differently in they rely on the air moving through the carb to lift the slide - but you have the same principal - you want the butterflies to be open exactly the same amount when cruising or opening the throttle.

My comment earlier about not relying on vacuum to sync the slide or butterfly is more for older engines.

Very related to this are the steps to help make a bike run smooth. If the tappet clearance/shim clearance is off on an engine, it does affect performance - esp. if you have a mix of tight and loose settings. So would having the ignition timing be off on a couple of the cylinders.

On my own bikes I like to set the valve clearances, then check the ignition timing before I touch the carbs.

That gives food for thought.
Steve

The carburetor holders with the vacuum plugs issue was cleared up by the other members of the group. I also found, ‘’through their help’’, a synchronization attachment port, and these would also serve to attach the vacuum lines, which operate the Air Suction Valve.
I am going with the OEM airbox for a 1980 Kawasaki KZ1000 B4 LTD.
These ''New'' carburetors are Mikuni RS34-D21-K. and I believe to the best of my knowledge, they are not constant velocity, as there is no butterfly valve in the throat section. These are flat slides.
The engine is not installed yet, so it’s difficult to tell how long the boots should extend between the airbox and carburetor. I don’t think anyone can help, until the correct measurements are confirmed.
In the meantime, I’m trying to get an idea of what’s available in 55mm, which is the out side diameter on the carb’s. From the possible matches I can then, focus on length.
I know in the end, I will need to modify the airbox openings to accommodate the larger duct boots.
This airbox is a rare part to be found, and will hate to change it, from OEM spec.

The Kawasaki 750 (early 80ties’) has the diameter I need, but not sure of the length…these look kind of short.
Suzuki GS 1100 G, GL, GK also have the proper outside diameter, which is 55mm
Best Regards

Daveo has a similar build. You might want to check it out. I used large hose as ducts. When I get home I'll measure the ID of the carb holders.
Steve

I was also thinking about this Radiator hose modification, but I'm looking to see if there is something out there with the least modification , for a clean result
This was my back pocket default plan.
There was a place on the web , that has all the stuff to mold your own, using silicone casting molds....and when finished is an exact replica of the part