Mikuni Carbs

[whiskey pete]

I am finally getting the top end of my beast back together. New rings, valve job, no porting with a stock cylinder and head. My question is that I have Mikuni VM 33 A 19 Carbs. They were so dirty that I am really surprised that the bike ran at all. I have cleaned them to the point of obsession, replaced all gaskets, float valve, and O rings. I want to come close to the correct jetting while they are still apart. The Main Jet is 135 and the Pilot Jet is 35. I plan on four individual air cleaners (not yet purchased), a Kerker 4-1 header with the baffle in, and installed Mikes Green Coils. I have set the floats to 24mm. Any suggestions on keeping the jets I have, or changing while the carbs are torn down. Also the vacuum line to the advance runs off the #1 carb manifold. The carbs were so dirty that I don,t have any reliable info as to plug color before I tore the bike down. Any suggestions on tuning and synchronizing. Thanks guys in advance.

[natemoen]

I am curious to see how the carbs work out for you some they are not the stock carbs. good luck man.

[CatatonicBug]

Also the vacuum line to the advance runs off the #1 carb manifold.

Is this just the way that particular version of carbs works? On the stock carbs, it's supposed to be on the #2 carb, and there is no place to connect it to #1.

[Jamie]

As far as tuning/synchronizing these carbs, I'm going the route of a Colortune kit for sure. I have other bikes and this will come in handy. Good luck.

[foreda]

Advance Port

I am finally getting the top end of my beast back together. New rings, valve job, no porting with a stock cylinder and head. My question is that I have Mikuni VM 33 A 19 Carbs. They were so dirty that I am really surprised that the bike ran at all. I have cleaned them to the point of obsession, replaced all gaskets, float valve, and O rings. I want to come close to the correct jetting while they are still apart. The Main Jet is 135 and the Pilot Jet is 35. I plan on four individual air cleaners (not yet purchased), a Kerker 4-1 header with the baffle in, and installed Mikes Green Coils. I have set the floats to 24mm. Any suggestions on keeping the jets I have, or changing while the carbs are torn down. Also the vacuum line to the advance runs off the #1 carb manifold. The carbs were so dirty that I don,t have any reliable info as to plug color before I tore the bike down. Any suggestions on tuning and synchronizing. Thanks guys in advance.

The vacuum advance line goes on #2 carb.

[natemoen]

The vacuum advance line goes on #2 carb.

If you noticed foreda, he has a different style carb so it may not go on the #2 carb. Put the advance line on the carb body that has the nipple on it. Whichever one it is on those carbs.

[CatatonicBug]

Is this just the way that particular version of carbs works? On the stock carbs, it's supposed to be on the #2 carb, and there is no place to connect it to #1.

If the carbs you have are anything like the stock ones, here's a picture that might help with the vacuum line routing. Do you still have the octy on your SF as well?

[Larrym]

VM33: Square One or BTDT???

I am finally getting the top end of my beast back together. New rings, valve job, no porting with a stock cylinder and head. My question is that I have Mikuni VM 33 A 19 Carbs. They were so dirty that I am really surprised that the bike ran at all. I have cleaned them to the point of obsession, replaced all gaskets, float valve, and O rings. I want to come close to the correct jetting while they are still apart. The Main Jet is 135 and the Pilot Jet is 35. I plan on four individual air cleaners (not yet purchased), a Kerker 4-1 header with the baffle in, and installed Mikes Green Coils. I have set the floats to 24mm. Any suggestions on keeping the jets I have, or changing while the carbs are torn down. Also the vacuum line to the advance runs off the #1 carb manifold. The carbs were so dirty that I don,t have any reliable info as to plug color before I tore the bike down. Any suggestions on tuning and synchronizing. Thanks guys in advance.

whiskey pete,

From what I've read here on the forum your VM33's can be set up to make your bike a happy camper. For the record you're talking about:

THESE CARBS:............................................ .............................And NOT These:Right???

..........

(Courtesy of http://www.wgcarbs.com/)

I'm not familiar with the exact settings or jet sizes cause I've got the BS34's on my XS Special. However, take a look at this:

http://www.xs11.com/forum/search.php?searchid=615818

It's a collection of threads here on the forum where the "keyword" VM33 is found in the discussions. (The Search Engine of this forum is your friend 24/7 and 365...)

Two more things:

First: The only person I am aware of that has the VM33's actually installed on his ride is a member named "The Wiz". He might be willing to share some details of his setup if you contact him through the PM (Personal Message) System here on the site. (Seems like a rather nice fellow all around IMO...)

Second: If the only place you have to place the vacuum advance line is on the intake boot "Nipple" (Censors please be kind...) then I'd suggest some form of inline dampener. The vacuum advance mechanism isn't designed to operate well or for very long with full manifold vacuum...


IMO it really is nice when someone adds something usable/useful to the overall knowledge base here. Gets tougher to find something that everybody doesn't already know or at least can't find documented somewhere by using the search function.

Proper Jetting recommendations for VM33's may/may not just fall into that category.

HTH

[CaptonZap]

Second: If the only place you have to place the vacuum advance line is on the intake boot "Nipple" (Censors please be kind...) then I'd suggest some form of inline dampener. The vacuum advance mechanism isn't designed to operate well or for very long with full manifold vacuum...


IMO it really is nice when someone adds something usable/useful to the overall knowledge base here. Gets tougher to find something that everybody doesn't already know or at least can't find documented somewhere by using the search function.

Proper Jetting recommendations for VM33's may/may not just fall into that category.

HTH[/QUOTE]


Check me if I'm wrong, not having done an indepth study of the carbs, but since you want advance in timing on engine speedup, you would not want the advance to work at closed throttle. I think the hose to the carb would have to go to a port on the carb that made vacuum as the flow through the throat increased, increasing the advance as RPM's go up.
Maybe someone that has studied these carbs can tell us. CZ

[crazy steve]

Check me if I'm wrong, not having done an indepth study of the carbs, but since you want advance in timing on engine speedup, you would not want the advance to work at closed throttle. I think the hose to the carb would have to go to a port on the carb that made vacuum as the flow through the throat increased, increasing the advance as RPM's go up.
Maybe someone that has studied these carbs can tell us. CZ

There was a whole thread about this a while back; you can see it here:
http://www.xs11.com/forum/showthread...=ported+vacuum

The short story is the mechanical advance (or TCI if you have a later bike) increases timing purely according to RPM; the vacuum advance is only supposed to add timing under lighter load (partial throttle) conditions. But Yamaha used an odd-ball 'ported vacuum' that gives no vacuum under closed throttle and dampens it during partial throttle. Connecting to the non-damped manifold port will cause an increase in idle RPM, as well as erratic timing due to intake pulses.

[Larrym]

Camera Man/Stunt Man and Scientific Research...

And here's the "follow up" thread with actual video of gauges hooked up to a bike while zipping down the highway/byway:

http://www.xs11.com/forum/showthread.php?t=28432

Science and data collection don't necessarily have to be boring...

[whiskey pete]

Thanks for all the input guys..Larrym the picture on the left is correct. Round slides. The vacuum line does have a dampner inline. When you run it full open( the dampner, not the engine) the engine sounds like its going to come apart with a wicked rattle noise. It comes from the advance unit. Turn the screw on the dampner and the sound goes away. All four of my intake manifolds have vacuum ports on them, of course three of them are capped. I will search VM33 on the forum to learn more and any additional info that can shead more light on these things would be great

[Rasputin]

Larrym the picture on the left is correct.

Is that my other left?

[Larrym]

Men-At-Work: "Down Under" Carbs?

Is that my other left?

Honestly...When I saw the carbs for the first time I thought the pic was upside down.

(Note to self: Seriously Question whether I should offer "help" to others....)

[crazy steve]

...The vacuum line does have a dampner inline. When you run it full open( the dampner, not the engine) the engine sounds like its going to come apart with a wicked rattle noise. It comes from the advance unit. Turn the screw on the dampner and the sound goes away. All four of my intake manifolds have vacuum ports on them, of course three of them are capped. I will search VM33 on the forum to learn more and any additional info that can shead more light on these things would be great

The in-line damper may only solve half the problem. The interesting thing about the factory vacuum hook-up is that it's blocked off (no vacuum) when the throttle blades are closed; this has to do with it's location in the carb throat. I don't know about your VM carbs, but the guys that tried a direct manifold hook-up got a high idle due to advanced timing from the manifold vacuum. Now, turning the damper down will reduce the pulses, but may reduce the amount of vacuum 'seen' and limit your total advance. This isn't an issue at WOT, but will hurt your part-throttle fuel economy. Just something to look at...