VM33 smootbores

otakar .if u accept what u have read above.u will not be disapointed with these carbs.
from what i have learned the only carb that will out perfrom these is the rs34,and maybe the keihin 33cr's and fcr's if u can aford them.certainly u cant find a better carb for less money for a mid size bore.the vm33's seem to real shine as u get to 1200cc's.
even on the stock engines they pull better than vm29's and bs34's acording to George.And lets face it George test rides these, on stock motors ,every day ,so he should know.
if the dyno says the 33's pull better at higher rpms then why would i want 29's.they wont feed your bigger cc's.

mark1122 wrote:

if the dyno says the 33's pull better at higher rpms then why would i want 29's.

Because most people don't spend the majority of time at the rpm that these carbs show the gains. I am talking on stock 900 and 1000's. Bigger cc needs bigger carbs so carb accordingly to your engines needs.

From what I remember reading a long long time ago, in a galaxy far far away; was this not the reason why Kawasaki went to the 26mm carbs from the 28s. I believe it was writen somewhere the 28s were too much carb for the 900 and the performance was "smoother" with the 26s.
I know I created the situation which is the subject here artificially, because I under jeted my 26s on my 67-900. I went to a jet one size smaller than stock with a MAC pipe on the bike (everything els being 100% stock)The bike quits pullinf at aboit 100mph unless I let up on the throtle and it starts to accelerate again. This is indicative of a lean situation.

Otto Kudrna

PS I will post some pictures of my GPZ1166 project sometime this week.

The 26s make more power in mid-range as the air speed through the venturi is greater because of the smaller diameter venturi. Heck, you can put 24s on a KZ1000 and it will run like a top... just when you get to where the cam profiles make the bike fun to ride, the 24s (and 26s) run out of gas. Problem with any of the VM series (24/26/28) that came on a KZ is that fuel pipes are the main jet... they are too small to support the potential of any 900/1000; even a stock bike. The 29s have bigger fuel pipes and with the right petcock/hoses, the 29s add a LOT of horsepower at the point where the cams kick in which is around 7K rpm on most stock bikes. The stock VM carbs more or less fall flat. The 33s OUTPERFORM the 29s at the same point where the 29s shine. Below 7K rpm, stick with 26s... I use VM26s on my KZ1000 shafty because that bike NEVER sees 7K rpm or revs much. I am looking for mid-range. The problem with the 33s is that unless tuned properly they have glitches in the area under 7K rpm where the somewhat milder 29s have fewer glitches. The 33s add some REAL zip to a stock KZ900; its just that you have to get them tuned to where they become semi-civilized at lower rpms and that has been what this thread is about. By the way, I tested about 400 sets of carburetors last year; 24s, 26s, 28s, 29s, 33s and BS series (BS32/34). When I test, I test for idle and maintaining steady idle, mid-range and higher rpm. I take each set tested to 8-9K rpm in 3rd and 4th and when the weather is good and I feel like it, run the bikes up a ways in top gear (just because I enjoy doing it I guess). Our carb test bikes are 903cc stock engines with good/consistent compression. Different exhausts and airbox combos. I use 903 engines because I have spare 903 engines, cylinder heads and block/piston sets that are easily swapped out. Just want to keep consistent on spare parts... could have easily have gone with 1015cc stuff I guess but I have about 5 spare 903 engines now so we won't likely change.

George.my Mikuni guide sugests changing the needle jets from 0-8 to p-2 to richen the mid.i'm thinking this may get us more fuel at wot since there will be more space around the needle only at wot.this may require less main?

I haven't found the Mikuni tuning guide very useful. It seems to be as useful as most of their initial tuning set up... not very. Perhaps they are right. The only way to know would be to buy a set of new needle jets and see. I am not sure these are still available; you could try Sudco. A larger needle jet will definitely flow more fuel regardless of which jet needle is used. Early Z1s used a P-6 needle jet as memory serves and then in 76, Mik went down to a O-6 or O-8... there are 10 sizes in each letter range... O-1 is the smallest, followed by 0-2, etc... a jump, like you suggested is pretty substantial; four sizes because the P range is larger than the O (OH) range. That jump really isn't all that dramatic... the size differences in one step size is actually very small and hard to measure. On street carbs, Mikuni stayed in the O range from 75 till 81 (when they went to cv carbs). The largest used was an O-8 and smallest an O-1 as I recall from specs in my head... Most of the richer carb set ups were oriented towards the bigger number with 0-6 common and most of the leaner spec carbs were around an 0-2.

Post edited by: wiredgeorge, at: 2007/09/05 09:04

my guide suggests that when u add a kerker you should go from
0-8 ,-4 needle clip,30 pilot,1.0 air jet ,140 main
to
p-2 ,-3 needle clip,15 pilot,.06aj ,and 130 main.

any idea what a 1 clip change would relate to on the needle jet?
i realy found my bike whent way rich whit a 1 clip change.
maybee i could raise it 1/2 a clip with some waser shims? or use a bigger needle jet instead?
have u tried rs34's yet?do u know what a modle D21-m is for?

I personally think the advice you provided from the guide is kind of insane... the needle jet size is a diameter. The main jet has a taper that moves in the needle jet so you would need to know at what throttle position the needle jet was in order to make a comparison. A Kerker would make the air/fuel mixture more lean and their recommendation was to make it leaner, as I understood it. I don't want to comment any more on the Mikuni tuning guide. I have never had any luck using any recommendation they have made.

WOW!I just tried the .06 air jets and it does have more throttle responce.mi bog moved down fro 4500 rpm to 2500.it accelerates week at 3000 and has a slight hesitation but way better overall. i was lean on top before.noe after 8 passes on a new plug i have just a hint of tan colour.where do we go now??? i could use a little more main or i could go down to .05 or.04 air jets.also i could go bigger on the needle jet?i'l have to see if i can still buy them.

G'day Mark and George,

Glad you've both tried experimenting with air jets. I first learned about the importance of this seemingly insignificant part in the late 80s when dialling in HS40s on Harleys. Did I mention that I hate "drag pipes' on street Harleys? But that' a whole 'nother topic.

My jetbox contains sets from blank to 1.5. Handy tool to have in the tuning arsenal.

Have fun,
Mick

nitro is there a point were u say that the air jet is too small?? should i get smaller 1's? how about bigger needle jets ,pro's and con's? not shure why mikuni suggested bigger needle jets but if there suggested smaller air jets worked then i guess i should try the bigger needle jets too. i just dont understand why on either 1 ??:blink:

Guys
I may sound like an Idiot asking this question; but since I have never mounted my 33s, what do all of you use for head mounting boots? Is there a boot made which has a large enough ID to take the 33s? Bit off the jubject, I have a set of 34mm "Amels" (on my 1103, 78 Z1R with Yosi pipe and stage 1 cams)what do you think of these carbs?

Otto