VM33 smootbores

The air jets have not turned up yet. When they do, it will take me awhile to get them installed... will wait till I am road testing some BS34s I guess and then toss them on after rejet.

You sync the VM33s by bench sync. I took an old set of carb holders and installed some vacuum spigots but they didn't seal well as the they were old manifolds and I didn't want to use silicon between the manifold and cylinder head.

I have gotten to the point where I can bench sync and most generally get the carbs within their spec when checking with a manometer. If I were to use VM33s all the time I would install some vacuum spigots on a set of new carb holders... cut the spigots out of the old rubber holders and drill and hole and push them through and seal with liquid rubber or something similar on the outside.

Thanks George, that makes sense. Cut, drill, hole, seal... another stock part bites the dust. Weehee.

i have some new (to me ) and interesting news to report on my vm33”s.i took it out to check the jetting on the new 35 pilots I just instald(had 22.5”s).the air screws where at 1 ½ turns out and I had no color on the new plugs during a plug chop test after 5miles of riding. I then ran the bike through the bog zone (3500 to 4500rpms) several times (7?) and stopped to check the plug(I only checked #1 plug each time). To my surprise I found the plug to be very rich (black). Then I reinstalled the plug and ran 10 passes from beyond the bog zone, 5000 to 8500rpm.this time the plug had cleaned itself and was white again.
So now I know that I am rich in the wot low rpms and lean in the wot high rpm” so what do I do with this now?????? How about the air jets?? if I reduce the air jet from 1.2 to .6 I should be able to reduce the mains from 140 to about 130? What can I expect from this? Any other ideas?
1.Also I found that at wot adding choke had no affect.
2. I can accelerate hard with no issues if I only open the throttle to ¾.
3.i don’t got a bog if I use wot at 3000rpm in 5th gear (it will pull right through the bog zone, but not strong, feels rich)but it bogs at all other gears below 4500rpm.at wot
4.turned pilot air screws in to 1 ½ = lean, 1 = rich,1 ¼ =good.

The air jets I ordered were shipped last week and when I get them, will let you folks know if they make a difference. The BLACK SOOT may be a bit misleading... when the bog occurs, it happens with the throttle wide open and essentially the bike isn't COMBUSTING during that time. This would make the plugs black with carbon regardless if the cause was rich or lean... I think that there is just too much slow air through the venturi with the throttle all the way open at this time so I guess you could call this a lean problem but not exactly in the traditional sense. Anyway, will report back on this issue when I learn some more.

today i raised the needle 1 clip to #4.it helped the bog a bit but felt rich at cruise.so i opened the pilot screws from 1 1/4 to 2 turns and thats a bit better .i will play some more tomorrow it was dark out.maybe i should put the needles back and increase the mains? or only raise the needle 1/2 a clip and add some main?i"ll keep at it.i am quite surprised that 1 clip would make it so rich.is that norrmal?it seems to go from lean to rich with 1 clip change on the needle.:side:

raising the needle definatly helped and opening the pilot air scew satisfied the cruise zone.so that is an improvement but not enough.i tryed takeing off the k&n's but it felt the same and if i added choke in the bog zone it got worse.if i added choke at high rpm wot it made no dif.
next i will try .06 air jets.

Mark, Got the .6 air jets installed and they do indeed make a difference. There is a hint of a bog at very low rpms when you crack the throttle all the way open but when you crack it open at 3K rpm, the bike doesn't bog like it did with the larger air jets. I tried using a #20 pilot jet initially and that was a bust... went to a #30 and that seems about right. Jet needles clipped to 4th slot. Pods/aftermarket pipes on a stock KZ900... I closed the air screws all the way. Running a #120 main jet. The main jet may be a little small... was hard to tell as I pulled 7500 rpm in top gear and it felt either rich or lean JUST A TAD... It was still pulling only felt like it was either starving for gas a shade or rich (I really couldn't tell which). I would go out and try some plug chops but it is Labor Day weekend and there is too much rural traffic and I suspect the DPS wouldn't buy my plug chop excuses hehe The 33s don't feel like other carbs; make me feel like there is a bunch of horsepower under me even if they are not quite as smooth as 29s.

I will try my .6"s tomorrow i hope.u must be rich at the top end now.by going from 1.0 to .06 u took air away so it will likely be rich.Greg Cope said u could go down 4 main sizes with this reduction in air jets .i suspect that as u go down on the main the bog will start to get worse ,since the theory we have been following says we were lean ar wot.it will be interesting to see? it sounds like they are working better for u than me.mine likes # 4 clip better for the bog ,but it went way rich at cruies(1/8 to 1/4 throttle.)so im still playing with the air screw,3Turns out now.2 1/4 caused a rich sputter.i'm suprized that u did not go way rich by raising the needle too?Glad to here u are making progress.I'm learning alot about the overlap of each circut .the books dont say enough about this.
Thanks for the update George.

The main air jet affects mid-range as well as wide-open throttle. I think that once we figure out how to tune these things perfectly, we will be the first ones on the planet to do so bwhahahaha I do like the acceleration though... it is addictive.

i was doing a plug check yesterday and cross threaded #2 spark plug. DAM.i will be down for a few days while i find a tap and helicoil. i'll let u know how the jets work out next week.Good luck with yours.

33's are too big for a stock motor Stick with the 29's.

Friend of mine was the dyno guy at a local shop. While the 33's made a little more top end power, the area below the curve was always better with the 29's. We are talking stock engines here correct? I have never beat the 29's performance on a stock or near stock engine.

Hi Guys
I have two sets of these carbs, and want to put a set on my scratch built GPZ1100 (actually 1166) I built this bike, or should I say am building this bike from a 81 1000CSR
To say the least I will have a lot of parts left over. All I am useing is the frame and the lower part of the engine. I would like to get this project finished within the next two to three weeks, so I am finding this thread very intrresting and informative.

Otto Kudrna