VM33 smootbores

So what is this entyre thread about?

Otto

I think this thread is about learning to understand the vm33's and this will tell us what we need to do to make them work there best. As Larry pointed out we are all learning from this. I certainly have. Not just about these carbs, but about the use off larger (or too large) carbs and what is needed to make them satisfy the motor.
Larry, Thank you for that info. That really helps to clear up the picture.
I think this statement by George says it all:
Re:VM33 smoothbores - 2007/08/09 19:52 My carb test bike has pipes/pods (one of them does as it is set up that way usually). It is a stock 903 with good and consistent compression. With a set of 26s it runs nice. With a set of 28s it runs nice... maybe more kick at the top with early Z1 carbs; later pumpers make little difference over 26s. 29s are an improvement over early z1 carbs when you hit 7K rpm. 34s are more consistent through the entire rpm range than are the 29s but at the top, maybe the 29s by a nose. The 33s will pull to redline insanely in 1st with no bog or slog, then in gears 2-5, if you shift over 4K rpm, the bike will pull your arms off... I would guess maybe 5 or more horsepower over the 29s and DEFINITELY more than BS34s.
Does this not tell me that the vm33’s are the best carb for this bike IF u want more power ?
I would say bs34”s come 2nd for price and vm29’s come in 3rd. we still need to add rs34’s to this list and when we do we will really had some great data. George if I get a set I would like to send them to u for a comparison so we can add them to your list.
u would of course have to believe what George says. I personally think he must have more ACTUAL SEAT TIME on each 1 of these carbs ,SIDE BY SIDE, than anyone I have heard from . Therefore should be more than qualified to make an ACURATE assessment.
It is important not to overemphasize the issue we are having with these carbs. They really do run well as a daily runner and in 90% of there chores .But when we ask them to work at wot WAY DOWN LOW (below 3000 rpm) ,they provide a week response (as George would say, when riding like a geezer). Not bad at all. Imo.
Also we have learned that as we increase cc’s we improve the signal and response. So as we near 1200cc’s they seem fine all around.
I think as Larry mentioned, the next step would be to try a pump. George do u have any donor parts ?

otakar wrote:

Please help

Subject: 1981 GPZ1100, .140 lift cams, 1985 GPZ head, Wisco 1170 kit Mac pipe. Where should I start with jetting on my VM33s.

Otto

if u start here u shoud be close.
pilot 22.5, airscrews out 2.1/2 turns,needle clip 4 from top, mains 147
this should be slitely lean, but will run fine.then u can increase to add color to the plugs.starting whith the mains then needles .when u raise the needle u will go richer and need to lean out the pilot. pm me when u get to it.

Post edited by: mark1122, at: 2007/10/02 09:39

Thank You Mark, I just cant stand hearing What I CAN'T do, I want to know what I CAN do. This info helps a lot. I think that the WEB 109 grind cams will provide enough vacuum to keep them happy enough. I will set up one of the sets as you sugjest. My 78-Z1-R will get the second set with the 76mm pistens, in the future.

Otto Kudrna

I was doing some reading today and just happened to find a factory manual for these carbs. In this are factory jetting specifications fore different bikes. For the KZ1000/1100 and GPZ1100 is this way
Carb Model# VM33-A14
Main Jets

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127.5
Air Jets

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1.2
Pilot Jets ----17.5
Jet Needle ----6DJ30-4
Needle Jet ----261 O-6
Throttle Valve-1.5
Air screw

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3/4 out

The Irony is that the Suzuki GS1100, even though it uses the exactly same carb set has totaly different jetting. I think that we are trying to over jet these carbs and run into problems at that point.

Post edited by: otakar, at: 2007/11/16 19:48

It's not good to start comparing your GPz to a GS1100 when it comes to jetting. You have to take each motor for what it is and work with it.

You're wandering into the "fussy carburetor zone" with those 33s. Many, many, many people have wandered there before you. It's the prime reason 33 Miks can be had so cheap on Ebay.

What generally happens is, you'll get them dialed in, the weather changes, you're back jetting again. They'll make HP. More peak than the 29's on a small motor. That's not the problem with them. If there is such a thing as a female carb....those are it:side:

i had my bike out last week. the temp was 7*c.it still runs as good as it did in august.all i can say for sure is they have been good to me.

I for one deffinately do not plan on giving up on them either.

mark1122 wrote:

i had my bike out last week. the temp was 7*c.it still runs as good as it did in august.all i can say for sure is they have been good to me.

mark1135cc
Senior Member
Joined: 09/18/06
Location: Canada
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Posts: 262 Posted: 10/21/07 at 4:15pm | IP Logged

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I when out on the back roads for my 1st ever test launch today. i came back puzzled. If i dump the clutch she stalls ? even at 8500 rpm. The front wheel would come up an inch and it would stall every time.i had too slip the clutch to get going. i know your suposed to slip the clutch but it shouldnt stall. Whats up with that?? the roads are cold and the tire didnt seem to be braking loose either ?? ive heard if u dont have enough spark u can blow out the flame ,but i have a new Dyna 2000 and 2.2 coils.?? 155 psi compression. could this be rich or lean ?plug color looks good .anyone have any ideas? same bike as sig bellow.
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76KZ900.1135cc 10.5:1 Wiseco's,k410 cams,1.5mm.over intakes,Heavy springs,shims under buckets,ported,VM33mm.smoothbores,Dyna 2000,2.2ohm coils,Kerker.Cobourg,Ont.Ca.
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Wow!:sick: ??????????????

Post edited by: modprod, at: 2007/11/21 16:40

This is USSUALY inicative of a lean condition. On carbs this big, when you loose a few RPM you will loose enough vacuum to loose fuel draw. This would be to either small pilot jets or the needle is too low. main jets would have very little to do with this. Your fuel float level could also be too low.

The 33s are not real hard to tune. You can use #17.5 pilot jets and shut the air screw and the idle and pilot circuit will work fine. The main jets Mark uses seem big to me but I test with a stock KZ900... I don't think it much matters what main jet is used unless it is too small... The big issue with the 33 is the bog when you transition from having the throttle open a small way at a steady speed to wide open suddenly. The big gulp of air slows air speed and the carbs starve for gas. The size of the pilot jet and needle position really are not all that critical in this issue. The slide cut out and pilot air screw are. Since the slide cut outs only come in one size (1.5) and that is about as small a cut out as can be found anyway, the real key is cutting down the size of the air jet from the stock 1.2 to about .5 or .6 (tried both and they worked about the same). You have to feather the throttle just a tad before cracking it wide open the the difference is pretty gratifying. The top end on the 33s makes small streetability issues seem kind of unimportant if you are trying to make horsepower. For reference, the 29s version air jet is .9 and a Z1 carb has a 1.0 air jet. The 29s have a 1.5 slide cut out and the Z1 carb has a 2.5 slide cut out (make sure you are using a bigger pilot jet) but the venturi is smaller making air bogging not really as much a problem.

As far as tuning a GS1100 vs a KZ1100, I know that if BOTH USE THE SAME BS34 carbs (such as those off a KZ1100), the identical jetting will yeild pretty much identical results. The same main jet is needed to be able to pull redline on either bike if pods are used. I think that as far as main jets go, there is some ability to guess what is a good number for either a GS1100 or KZ1100 but as far as pilot jets, not really as Suzuki does the internals on a BS34 differently than Kaw does but main jets will be about the same. Suz tends to use puny main jets in all its larger bikes from the GS750 to the GS1100 for some reason. Kaw likes a bit richer jetting. Dunno what the thinking is.

SIDE NOTE: Purpose of thread is to discuss tuning VM33s. Since there are so many out there and they don't have a great rep, it seems useful to see if I can get them to work well on the street. Notice that 29s have reached the point of crazy as far as pricing goes and while 29s work better than 26s/28s, it isn't by all that far a margin although they are fairly easy to tune compared to the 33s. Since few folks run 33s, it is fun to chat with guys like Mark who are serious about testing and performance and not afraid of trying things. He is the kind of guy that helps keep this sport fun for an older guy like me. I like positive dialog... Like Otto, when someone tells me something can't be made to work... wellllll I guess that is what sets me to making it work.

Post edited by: wiredgeorge, at: 2007/11/21 16:55

I beg to differ. Jetting is very easy to change in these carbs. To "properly tune" these carbs in a small bore application is next to impossible. The closest to acceptable low speed throttle response I've personally witnessed was in the mid 80s when an accellerator pump (available at the time) was abapted to these carbs. That helped the low-speed throttle response somewhat. However when campared to 26/28s on a stock motor 900/1000 the little carbs will walk the 33s all day long! Some thought the 33s worked good because after they rev'd past the unresponsive zone they "seemed to pull very good, however by this time the guy with the "little carbs" would be gone!

SIDE NOTE: The question was proposed:
(I have a couple questions..
These carbs tend to bog when you are in a higher gear at a lower rpm and crack the throttle all the way open. Doesn't seem to matter what gear. Anyone experienced that issue and figured out how to fix it... Example... 40 mph constant speed in 3rd gear and then open throttle fully. BOGGGGGG... if you let the throttle off just a tad, the carbs will then pull like a freight train. Seems to do this with most sets of 33s. I have used mains from 120 to 150 and pilots from 17.5 to 30 and all combos of jet needle clip positions and still see this issue on most sets)

I only tried to answer this question as best my experience dictates. If someone proves otherwise "more power to them" you are to be congradulated! He was able to do something nobody else has been able to do (alter the laws of physics)
If someone says: you can't stick you head up your butt and come out smelling like roses! I'll take their word for it.
There are "much better" carbs than 33s but more expensive. I'll stick with that.