TOPIC:

There is mention of late model mikuni 29s recommending 25 pilots for the kz900
seems big ,I've always used 17.5

Can anyone point out the difference between the early and late model

Is it best to use the 17.5  in the late model 29s in my stock kz900 application 

What is a "late model" VM29"?

That could depend on the slides, air jets, etc. 
Steve
www.jetsrus.com/carburetor/carb_mikuni_V...oded_view_parts.html

I think this info, that posted by OP, came from jetting guides from both Z1 ent and Sudco, as both do indicate larger pilot jets. I did a rather quick search for this info but did not find it on the newer Z1 ent site.  In the past I did pull down tet from both sites,  Here they are 

z1 enterpirse jetting guide from www.z1enterprises.com/reference/z1-carb-guide.aspx

Below is a reference of jet settings for the 29mm carb on Z1 / KZ engines.  This is a good starting point for a bike with 4-1 exhaust, after market cams (up to 0.410" lift) and high compression pistons (approx 10.5:1).  Each bike setup is different, so actual settings will vary.

We have included the Honda CB750 settings as a reference.  You will notice the similarity of setup - so.... if you can find a set of 29mm carbs off a CB750, they should work on a Z1.  The same is not so true with smoothbores setup for the Suzuki GS range.  The slide cutaway is different (2mm) - yes, you can still buy new slides, but they are expensive.


28mm (VM28SC)  Z1 & early Z1-A 
 Main Jet  112.5 
 Air Jet  1.0 
 Needle Jet  P-8 
 Jet Needle  5J9-3 - last number is the clip position where 1 is at the top of the needle (leanest) and 5 is at the bottom (richest) 
 Throttle valve (slide)  2.5mm cutaway 
 Pilot Jet   20.0 
 Air Screw setting  1 1/2 turns out 
    
 28mm (VM28SC) Late Z1-A & all Z1-B 
 Main Jet  112.5 
 Air Jet  1.0 
 Needle Jet  O-8 
 Jet Needle  5J9-2 (last number is the clip position) 
 Throttle valve (slide)  1.5mm cutaway 
 Pilot Jet   17.5 
 Air Screw setting  1 1/4 turns out 
    
 26mm (VM26SS) KZ900A4 & A5 
 Main Jet  115 
 Air Jet  1.0 
 Needle Jet  O-6 
 Jet Needle  5DL31-3 (last number is the clip position) 
 Throttle valve (slide)  1.5mm cutaway 
 Pilot Jet   17.5 
 Air Screw setting  1 3/8 turns out 
    
 29mm smoothbores  Z1 / KZ900 / KZ1000 
 Main Jet  120 
 Air Jet  0.9 
 Needle Jet  O-6 
 Jet Needle  5DL31-3 
 Throttle valve (slide)  1.5mm cutaway 
 Pilot Jet   17.5 or 20.0 (or 25 in the later versions) 
 Air Screw setting  1 1/2 turns out 
    
 29mm smoothbores  CB750 
 Main Jet  115 
 Air Jet  0.9 
 Needle Jet  O-6 
 Jet Needle  5DL31-3 
 Throttle valve (slide)  1.5mm cutaway 
 Pilot Jet   17.5 or 20.0 (or 25 in the later versions) 
 Air Screw setting  1 1/2 turns out 
    
 29mm smoothbores  KZ650 
 Main Jet  105 
 Air Jet  0.9 
 Needle Jet  O-4 
 Jet Needle  5DL31-3 
 Throttle valve (slide)  1.5mm cutaway 
 Pilot Jet   15 
 Air Screw setting  1 1/2 turns out 

FROM SUDCO
Application Carb 
Model Main Jet Air Jet Pilot Jet Jet Needle Jet Float Throttle Valve N100.604 BS30/97 VM22/210 Needle #261 Series Height VM29/15
Honda CB750 (SOHC) -1978 VM29-A2 #115 .9 #17.5 #5DL31-3 0-8 23mm 1.5
Kawasaki KZ650 (77-79) VM29-A7 #120 .9 #25 #5DL31-3 0-6 23mm 1.5
Kawasaki KZ900 (76-77) VM29-A7 #120 .9 #25 #5DL31-3 0-6 23mm 1.5
Kawasaki KZ1000 (77-80) VM29-A7 #120 .9 #25 #5DL31-3 0-6 23mm 1.5
Suzuki GS750 2-Valve (77-79) VM29-A12 #115 .9 #25 #5DL31-3 0-6 23mm 2.0
Suzuki GS1000 2-Valve (78-79) VM29-A12 #115 .9 #25 #5DL31-3 0-6 23mm 2.0
Float Height  All sizes 17mm

On my Z1B, 1015CC, 29 pumpers i use 115 mains and 17.5 pilots, airs crew 1 turn out.