VM33 smootbores

u can use boots from a j modle. Sorry , no info hear on the Amels. u will like the vm33's. i think they are the best for the money.

Mark
I tryed the J model boots and they are quite a bit undersized. I imagine they will stretch a bit. I hope they don't split with time.

Otto

the j boots are what i have read as the recomended boots.my bike already had boots so i cant say for sure what mine are? mine are tight but i get no sence that they could split.pm george, and ask him.

There are three different carb holders used to mount BS34 carburetors. Any will work fine but you should match the profile of the venturi edge with the profile on the inside of the carb holder. This will stress the carb holder the least because not many folks use the 33s with an airbox which would support the carburetor assembly as the bike bounces. Since you will use pods, I suggest you use cable ties to support the carb assembly as this will add greatly to the life of the carb holders. I use J style carb holders for all my VM33 testing and probably need to take a close look at the different styles of flanges and carb holders and put together a list... put this on my project list of things to do.

Thanks George.just a note for your files.i use a stock petcock valve on my 1135 with vm33's ,37.5 intakes and full port job, and have never had any sign of fuel stavation.so i dont see a need for a pingle valve at this cc level. i did however install my valve reversed to gain clearance.it used to hit the carbs when i had an ltd tank.

I use Drag Specialties petcocks and these are supposed to be high flow. Haven't run out of gas with them but I test with stock engines. I use the same petcock on both my test bikes and my personal bikes with a Pingel adapter plate.

I’, getting there. i raised the needle to #5 today and found more improvements. I also went up to 147.5 mains and down to 122.5 pilots. lots of tests ,and 2 stripped plug holes later. i lowered the bog zone another 500 rpms, to 2000rpm. It falls on its face at wot from 2000 rpm. At 2500 it pulls slightly rough and week. 3000 pulls clean.
When I hit it wot at upper rpms and let out to ¾ throttle it flutters then cleans right up. this has grown as i add bigger mains and needle.but the bog has got better. It pulls harder on wot than ¾’s. any ideas?
where do i go now as far as the bog goes ?.everything was lean when i started and all systems seem to be fed properly now.sudco does have larger needle jets. funny thing about the bog zone is the plugs read rich.yet adding fuel everywhere seems to help.


Post edited by: mark1122, at: 2007/09/12 17:55

Post edited by: mark1122, at: 2007/09/12 18:24

I tried going back to smaller 140 mains today and the bog zone got slightly worse and the flutter when I back out of wot got better. So I think I will go back to the 147.5 mains. I may try larger needle jets next but will have to order them from Sudco.

mark1122 wrote:

otakar
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.

Had Mikuni either included or made available, an accelerator pump for those things, that would have been the best thing available. Would have made acceleration way better and allowed for proper cruise jetting.

You guys are trying to band-aid jetting to overcome a velocity related problem.

That is my opinion and it's not meant to stop you guys from your efforts in trying to tune those things. Good luck, have fun and learn a bunch along the way....But let's not just stagger into this blindly. Let's apply some science to the madness.

Here's a carb size formula that's good for ballpark carb sizing if you don't have the facilities to actually measure air speeds. It's not the bottom line because all carbs are not created equal. It's better than nothing. By using it, you can establish some baselines. Use what you know works for a given motor combo in conjunction with the formula to your advantage.

Especially where lower RPM acceleration is concerned, these target values are good.

Target velocities below 250FPS are low.
Target velocities of 300FPS are desirable.


V= (Sx2)/304.8 X (RPM/60) X (D-Squared / d-squared)

V- Mean air velocity in FPS [target 300FPS]
S- Stroke in mm
RPM- point of max torque
D- Cylinder Bore mm
d - Venturi Diameter mm

When the numbers are run for a stock KZ1000, using a target velocity of 300FPS, it's 28mm carbs that fit the bill with 293FPS velocity calculation.

For 33mm carbs it's 211 FPS...way low for good acceleration from low RPM.

For 1075cc [72mm bore] it's 223FPS

For 1166cc [75mm bore]The 33s jump to 242FPS. Much improved.

Fuel moves through carburetors as a result of pressure differentials or it's forced via a pump.

Fast air has less pressure than static air. Equal out the pressures and fuel just plain stops flowing.

Yank open the throttle at low RPM with a too big carb and the velocity drops. To overcome this for acceleration purposes, we force fuel in with a pump [if available].

No pump on carbs that are already too big for the RPM range....ok....band-aid them with too large jetting for best cruise A/F ratio.

That scenario is essentially the purpose of CV carburetors. Let the motor tell the slide what it likes rather than the rider ignoring the motor and demanding the carbs do something they were never designed to do for that particular engine.

Problem with CV carbs is they can be flow killers with that throttle plate and arm stuck in the way.

So there's some velocity math to use. The other part of the equation is the length of the intake tract. Longer velocity stacks will improve mid-range. Here's a formula to help you establish the length of the intake tract. The entire length.

Length = 132,000/RPM

Have fun with the jetting efforts! Don't let anything or anyone stop you from learning!

Larry C

PS - George...You're a pretty clever carb guy. Why don't you try to adapt an accelerator pump setup to the 33s? Nail it down and you can probably sell a bunch of them...

Post edited by: larrycavan, at: 2007/09/15 08:38

When I went to the 33s at 1170cc I had
some fuel starvation with the stock petcock.
I have used a Pingel with the reserve on it
for years now.

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

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

Sorry, but 33 SBs are a poor choice to start with on anything really. These are the "Lemon" of the carb world. After all this money you've spent why not pick-up some 36RS carbs. These would be an infinately better starting point. I realize the 33s got real cheap but there is a reason why they got so cheap! Not a very good carb.

Post edited by: modprod, at: 2007/09/21 16:09