26 and 28's performance differences

I was wondering what the performance gains and losses between 26 and 28mm pumper carbs? currently I am running 26's and am happy with the the performance, and the way they fuel is spot on, I also have a set of 28 pumpers which I have cleaned and refurbished, these are the anti tamper type which are completely stock except for the air screw, it is modified so it does not need the plug to seal it.. so what is the general pros and cons.

Following with interest Kev. 
I'm no fan of CV carbs which were stock on my 1000J. I had a set of 26's so used those in my build. It ran fine with them and rev'd cleanly right through the rev range. I then changed the top end to 1100 and thought bigger carbs would be the thing to have. I bored out the 26's to 30mm and ran with those. Apart from a little bit cleaner and quicker revving I didn't really notice a difference in performance. 
The next step was to add an oil cooler, now that really improved performance in all aspects! 

Not sure any of the above helps or hints to answers for your question but just my experience with bigger carbs. 
Be interested to see what other experienced members have to comment on the subject. 

kevski wrote:

I was wondering what the performance gains and losses between 26 and 28mm pumper carbs? currently I am running 26's and am happy with the the performance, and the way they fuel is spot on, I also have a set of 28 pumpers which I have cleaned and refurbished, these are the anti tamper type which are completely stock except for the air screw, it is modified so it does not need the plug to seal it.. so what is the general pros and cons. 

I don't understand the bold/underlined parts.  What are "anti tamper type"?  And what "plug to seal it" are you referring to?  

Nessism wrote:

kevski wrote:

I was wondering what the performance gains and losses between 26 and 28mm pumper carbs? currently I am running 26's and am happy with the the performance, and the way they fuel is spot on, I also have a set of 28 pumpers which I have cleaned and refurbished, these are the anti tamper type which are completely stock except for the air screw, it is modified so it does not need the plug to seal it.. so what is the general pros and cons. 

I don't understand the bold/underlined parts.  What are "anti tamper type"?  And what "plug to seal it" are you referring to?  

Lost me also 28 pumpers have air pilots that have no plug over them.

Mikaw wrote:

Nessism wrote:

kevski wrote:

I was wondering what the performance gains and losses between 26 and 28mm pumper carbs? currently I am running 26's and am happy with the the performance, and the way they fuel is spot on, I also have a set of 28 pumpers which I have cleaned and refurbished, these are the anti tamper type which are completely stock except for the air screw, it is modified so it does not need the plug to seal it.. so what is the general pros and cons. 

I don't understand the bold/underlined parts.  What are "anti tamper type"?  And what "plug to seal it" are you referring to?  

Lost me also 28 pumpers have air pilots that have no plug over them.

Some pumpers have short air screws and anti tamper caps (Welch plugs)  pressed in the body so that the settings cannot be altered.
The caps need prising out to get at the air scrrews.
 

These were also common place in the European car world as emmision regs got tighter in the 80's

The air screws picture have 1 original type short air screw that was factory set and then plugged over, the other 4 are modified so they can be adjusted, as you can see instead of being threaded at the top they are threaded halfway down, the four rings are to sleeve the original plug hole so the o ring keeps it airtight, but enough about that, what of the pros and cons of 26's against 28's?

kevski wrote:

The air screws picture have 1 original type short air screw that was factory set and then plugged over, the other 4 are modified so they can be adjusted, as you can see instead of being threaded at the top they are threaded halfway down, the four rings are to sleeve the original plug hole so the o ring keeps it airtight, but enough about that, what of the pros and cons of 26's against 28's? ]

On a stock motor the 28's are worth around another 7bhp and have more flow potential for a modded engine.
These are the only change to the Z1R etc that upped the power from a claimed 87 to 90..
 
 

Carbs are intended to provide roughly 15/1 air/fuel ratio.  Somewhat richer at low speed and leaner at highway or higher speed.

At higher speeds the smaller diameter carbs would restrict air intake, not fuel.  Fuel flow can be adjusted by changing internals so that it matches air flow.  On a stock engine you would reach maximum speed sooner with the smaller carbs, and it would be lower than with the larger ones.  

On my KZ1000 I installed a set of 1976 VM26SS carbs.  They perform just as well as the stock VM28SS pumpers at any speed I care to travel but I suspect my top end is compromised.

Following up on above  .
Back when new My 78 LTD came with 26's
My good friends Z1R    came with 28's
We raced from every traffic light and stop sign.
I was faster at the start  , but he would pull on me  once over  about 60 mph   
I jumped up to 29 smoothbores and we were even down low , but I pulled slightly on him
above 60 mph
This was before pipes , cams , gears , and all other mods happened

I have put them on today and had to take them back off, a particle of crud had jammed a float needle, back on and running idling really well, very responsive, than the 26's crisper, working realy nicely at lower throttle, opening up under load a little bit fluffy, looking to change main jets from 102.5's o 105's, I have a set with no markings on them so if anyone knows the hole size in mm I would appreciate it if you could tell me.

What bike are you riding?