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General Category >> Rubber Side Down! >> Mikuni VM vs Stock Carb, Advantages/Disadvantages
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Message started by d3adrock on 12/26/19 at 06:56:19

Title: Mikuni VM vs Stock Carb, Advantages/Disadvantages
Post by d3adrock on 12/26/19 at 06:56:19

Hi, I'm currently debating whether I should rejet my current carb or get the mikuni vm preformance carb, with the thunder products upgrade parts, like the UFO, (don't want the dialajet since it seems slightly delicate) However I don't really understand the advantages that the vm makes over the stock. Obviously I want as much power as possible, but my main concerns are, realiability, durability, and longevity, followed by power, in that order. What advantages would the vm offer in those regards? I understand one is CV and the other is mechanical meaning the cable conects directly to the slide as opposed to a butterfly, however I still dont understand what the means in regards to power, feel, and all the other categories. Thanks for all your help!

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by Fast 650 on 12/26/19 at 07:34:38

The main difference is in throttle response. The CV relies on vacuum to raise the slide so there will be a slight time lag from the instant that you twist the grip until the slide starts to raise. That will make the VM feel like it is making more power than the CV carb does just because it reacts quicker. The CV carb can be tuned to lessen that lag time, but there will always be some amount of lag compared to the mechanical VM.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by d3adrock on 12/26/19 at 07:53:09

Does that make it more likely to be flooded or is the difference not that extreme?

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by Fast 650 on 12/26/19 at 07:54:53

Lancer would be the man to ask on that one, he knows the VM quite well.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by d3adrock on 12/26/19 at 08:00:31

I tried messaging him but didnt hear back, probably due to the holidays. In the meantime I thought I'd open the question to the greater forum!

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by Fast 650 on 12/26/19 at 08:08:08

Another variable is what mods have you done to your engine, and what mods are you planning down the road. If you are staying stock or near stock, I would stick with the CV myself as it performs well enough in that instance. If you go with a ported head, better exhaust, hot cam, bigger bore, etc then the VM would show an advantage over the CV.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by d3adrock on 12/26/19 at 08:10:07

I upgraded to a delkevic exhaust, and it's running very lean now which is why i'm in a bit of a hurry to figure out my carb situation before it gets much yellower. Also side question? can you rejet the carb without taking it out? Is it difficult?

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by Fast 650 on 12/26/19 at 08:25:08

Okay, get your jetting dialed in first. You can change the jets without removing the carb. If you loosen the clamps holding the carb you can rotate it to gain access to the float bowl screws. While you are at it, if you haven't done so already, raise the needle too. Search for the white spacer mod on the forum and you will find what you need for that. Usually two or three #4 washers to replace the white spacer will do the trick. If you order Lancer's jet kit it comes with (I think 3) pilot jets, main jets, and the #4 washers.

Getting the overly lean factory emissions jetting dialed in to something better suited for performance makes a huge difference. You will like the change in performance that makes even on a stock bike.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by Gary_in_NJ on 12/26/19 at 09:40:49

DragBikeMike made a thread on the various carbs used on the LS650, complete with dyno pulls. He includes his thoughts and opinion as well as hard data.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by d3adrock on 12/26/19 at 10:59:58

Cool, just finished reading it, as cool as an s&s carb would be I think thats a little too much for me. From a purely reliability/durability standpoint would a stock cv be better than a vm? or would the vm be better because it has less parts?

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by Gary_in_NJ on 12/26/19 at 11:18:28

On a stock or nearly stock engine the OEM carb is fine. In fact, it suits the character of a cruiser well. It’s when you’re no longer riding the bike like a cruiser, and/or when you are demanding more from the engine, when you may benefit from a different carb. At WOT, it really doesn’t matter. Fast throttle transitions will benefit from a cable actuated slide. Dirt bikes and track bikes are two types of bikes (and styles of riding) where I think a cable actuated slide are necessary. If you need the last fractional horsepower from your Savage, I’d strongly consider a carb upgrade.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by batman on 12/26/19 at 12:30:25

It doesn't seem to me to make sense to spend money on a new carb ,when you could do the spacer mod ,and replace your main jet with one slightly larger (150 main is a good all around jet ) at a cost of about $15 , that would solve your problems. I would invest in J.I.S. (Japanese Industrial Standard ) screwdrivers to avoid stripping the screws on the carb .

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by d3adrock on 12/26/19 at 12:47:54

My thinking was that if i was gonna go through the trouble of adjusting the current carb, I might as well upgrade the carb for better performance, however, the more i read the more it seems unnecesarry for my needs. I don't necesarrily want a super choppy throttle, as my throttle control isnt the best. Mostly i was thinking it would give me more power in the low range, however that might be mistaken.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by batman on 12/26/19 at 13:08:16

I think either carb won't effect your low range power ,doing the spacer mod will increase it ,again with ether carb. A weaker low range is usually effected more by a change to a higher performance cam ,as they raise the torque peak to a higher rpm.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by Ruttly on 12/26/19 at 13:16:33

Here's my 2 cents worth. DBM is the most extreme/educated/creative
R & D guy around. We all have something to learn from him. The stock carb is good and is quite smooth , with some rejetting and a pod filter is the cheapest way to go. My R & D style is all by feel with almost no record keeping. Build it , tune it , ride the crap out of it. The Mikuni 36 VM is a super simple highly effective carb. The one I got from Lancer came prejetted and it was perfect,after providing him with all the needed info.
VM will give you instant throttle response and feels like it increases the width of the power band as well. Parts are easily available. Super easy to install and tune/jet and also has some upgrades too. If you like smooth acceleration stick with the stocker , if you want some $hit n git buy the VM kit from Lancer. It's my first choice for a replacement carb and been using them for 40 years.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by d3adrock on 12/26/19 at 13:44:19

I've been trying to buy from lancer for about a week now, havent heard from him yet. Wider power band sounds like something i would want, im not sure if i want smooth acceleration or fast throttle response. What does that feel like comparitively.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by Gary_in_NJ on 12/26/19 at 17:52:14

7B2C7E7B6D707C741F0 wrote:
Mostly i was thinking it would give me more power in the low range, however that might be mistaken.

If you want more power and throttle response in the low range (say 4,000 rpm and below) then a carb with a SMALLER throat is what you want.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by batman on 12/27/19 at 06:25:26

You can get faster throttle response from the stock CV carb as well, both DBM and I have done it ,I increased the size of the vacuum ports( the two tiny holes in the base of the slide) ever so slightly , that allows the vacuum above the diaphragm to build/ recede faster, lessoning the delay , DBM 's answer was to drill a third hole and that's a better way ,because if you drill the third port to large , and find that it reacts to fast (a lot of backfires if the slide drops to fast) you can plug it with a screw and return the carb to stock, or you may be able to make adjustments to the TEV valve.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by srinath on 12/27/19 at 06:36:15

Oh on the GS500 we have the opposite problem, especially when you put K&N and pipe on, slide rise too fast. We plug 1 of those holes and some jet kits even constrict the other one.
Cool.
Srinath.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by d3adrock on 12/27/19 at 07:34:00

So if i am undderstanding correctly, there is little power increase, but an increase in responsivenes? Aside from reliability i was hoping for some more power. In regards to the fast response, would that increase the popping on slowing down? I have a tendency to slam the throttle shut when stopping abrubtly (which i like to do quite often) would the vm carb be bad for that?

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by batman on 12/27/19 at 08:38:13

Yes ,with the VM you need learn to roll the throttle on and off ,and may not even be able to close it fully until the motor drops down to idle speed, to prevent backfire.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by d3adrock on 12/27/19 at 09:02:47

Thanks for the info, forgive my noob like motorcycling skills, but if thats the case how do i come to a quick stop?

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by Eegore on 12/27/19 at 09:34:28

I can compress the clutch and stop with the throttle fully engaged by using the foot brake so I'm not sure what your question is.

By "quick" stop do you mean emergency stopping? If that's the case I could care less what my exhaust does since I'm concerned about saving my life.

Or are you saying your riding style is one where you like to stop in as short of space as possible? (not recommended by the way)

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by d3adrock on 12/27/19 at 09:40:15

I always use both breaks when stopping (except in a turn), and i'm probably saying that my riding style is such that I like to stop in as short a space as possible. Why is that not recommended? It's allot of fun!

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by batman on 12/27/19 at 09:45:02

Nor is tailgating , leaving a few car lengths between you and the car in front of you tends to make the car behind you think like wise.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by d3adrock on 12/27/19 at 09:50:55

Well, i definitely dont tailgate, and i dont brake hard when theres others on the road, i understand the safety dangers of stopping hard in traffic, but i meant more so in general. Im probably exposing my ignorance here but do most people not stop as quick as they (safely) can? And if so, how do you do that with out using the front brake?

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by Eegore on 12/27/19 at 10:12:00

"Why is that not recommended? It's allot of fun! "

Its unsafe to drive a vehicle of any kind at speed and slam on the brakes to use as little space as possible to go from travel speed to no speed.

To me the term "in as short of space as possible" means using as little road space as possible, which can be confusing to other motorists.

This means you are either getting as close as possible to another vehicle before hitting the brake, which is very unsafe. Or slamming the brake to stop as short as possible, then moving forward again to get into the appropriate spacing for traffic. Or you are just slamming the brakes and sitting 4 or 5 car lengths back at a stoplight.

This must just be a terminology difference between us. I do not always try to stop as fast as I safely can, I regularly coast to a stop, or engine brake etc.

I think you may just have to make a compromise between your riding style and they type of carb you want, but I'm no expert on carbs for sure.

If you go with VM to get more efficient throttle response and also want to let up on the throttle immediately to 0% then you will most likely experience popping, I do on all my bikes.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by DragBikeMike on 12/27/19 at 15:56:30

It would be good to know if your carburetor is completely stock, or if it has been modified in any way. Are all the jets original? Is the brass plug still in place over the idle mixture screw? Has the needle in the slide been repositioned?

If the carburetor is completely stock, and no re-jetting has been accomplished, you will be pleasantly surprised at how much better the engine runs after doing the mods found on this forum. Readjusting the idle mixture and raising the slide needle a bit work wonders. It’s like a completely different motorcycle, and it's free. 8-)

However, if you are anything like me, once you live with the re-jetted carburetor you will find yourself wanting some more steam. The VM flows more air, and more air means you can add more fuel. More air + more fuel = more power.

Why don’t you order the VM from Lancer? It’s a complete kit and hassle free. The 36mm will flow about 8% better than the stock carb. While you are waiting for the kit to arrive, you can go through the stock carburetor and learn a whole bunch. It will be informative and fun. Take lots of notes and pictures.

Live with the re-jetted stock carb for a while. Compliment your souped-up carb with a bit more airflow by modifying your airbox. Then, when you are confident that you have the carburetor & airbox optimized, install the VM. That way, you will have first-hand knowledge on the merits of both mixers.

Do a nice report that covers all the ins & outs of the project and provides your perspective. It won’t cost anything to tune-up the stock carb and modify the airbox. It will be very gratifying to see how much you improve the performance. Installing the VM will give you a nice kick. You won’t be disappointed. When you are all done, your post will be most appreciated. You will feel like a million bucks.

Rutly, I’m both flattered and embarrassed. This forum is loaded with expert members (including yourself) who all contribute top-notch advice. I am far from the sharpest knife in the drawer.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by d3adrock on 12/27/19 at 16:10:33

Thank you for your advice, i really appreciate it. My carb is tottally stock as far as i can tell except it doesnt have the brass plug, and i messed with it and the idle screw, to stop it from dying while i was on the road. I plan to buy one form lancer as soon as i hear from him. Just incase i missed it, is there a thread with instructions (perhaps even pictures) on how to rejet, it will be the first time ive rejet my own carb and am a little nervous, is it the sortof thing a newbie can do? I already have the jets. Right now Im on the search for comparison of others who have made the switch. If/when i do it i will certainly post my experiences here!

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by Ruttly on 12/27/19 at 19:01:52

It's called the Sudco tuning manual. I got mine with my carb , not sure if they still come with it , but they are easy to get.Ask Lancer about it.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by Ruttly on 12/27/19 at 19:52:24

Sudco manual online Amazon/eBay/etc $12 and up

A true must have,still use it after all these years.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by d3adrock on 12/27/19 at 20:00:14

Can you give a link or post the specific name? I looked but there are several and i'd hate to get the wrong one

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by Ruttly on 12/27/19 at 20:18:21

Don't buy one till you talk to Lancer.
Think they are all the same just different covers
Mine is the older white cover

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by d3adrock on 12/29/19 at 15:38:15

Ive changed my mind have decided that im going to get a weisco 94mm piston and stage 3 cam. My question in regards to carbs is, has anyone gotten a vm and either regretted it or preffered the feel of the cv? Thank you to everyone who has posted so far, i really appreciate it!

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by batman on 12/29/19 at 16:24:09

You haven't even tried a spacer mod on the CV carb, but your ready to rebuild the entire top end of the bike ? I hope you're knowledgeable .Good Luck!

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by d3adrock on 12/29/19 at 16:29:26

To be perfectly honest, i was planning on taking it to a shop and having them do it all at once. I hope i dont lose any diy karma

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by IslandRoad on 12/29/19 at 21:44:43

I've got one of those high-comp pistons sitting on my desk next to me. I've had it a bout a year - waiting for an opportune time to do the swap. It'll be my first project of that nature (I just got in touch with a local engine rebuilder who can hone the cylinder for me).

Having said that, the piston does look so very very shiny and nice!!

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by Eegore on 12/30/19 at 15:20:21

My question in regards to carbs is, has anyone gotten a vm and either regretted it or preffered the feel of the cv?

I have 3 1995's and one has the VM, I do not see any reason to go back to the stock carb other than to reduce the responsiveness of the throttle. This bike also had IntelaJet installed after about 6 months of the VM by the employee that rides it due to the altitude changes where the bike is.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by LANCER on 01/01/20 at 04:27:51

Having an appropriately sized and good flowing exhaust system I find to be an important component in insuring that the engine runs smoothly accelerating or decelerating. My engine does not backfire (shotgun blast) but it does crackle & pop on decel and that sound I love. To me, that is a healthy sound.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by d3adrock on 01/01/20 at 09:33:20

Do you find that it's still possible to get a somewhat smooth acceleration? Or is that all down to throttle control? Also i'm a little concerned about flooding the engine, or is that not a concern? Thanks!

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by Dennisgb on 01/01/20 at 10:23:23

37603237213C3038530 wrote:

A properly set up engine should have none of the problems you describe. Flooding is when carb is too rich...way too rich.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by LANCER on 01/03/20 at 16:14:36

36613336203D3139520 wrote:

I get smooth acceleration, the only thing is just the nature of a round slide carb without an accelerator pump, and that is the brief pause when going from idle to WO instantly on the grip. It just is. No biggie though, I can get and go as quick as needed. I am a senior but I’m one that enjoys a healthy, good handling, hard accelerating, and responsive ride. That is fun.

As mentioned, flooding is not a issue.

Title: Re: Mikuni VM vs Stock Carb, Advantages/Disadvanta
Post by d3adrock on 01/03/20 at 16:25:50

Awesome, that sounds perfect. Ive decided, no time like the present, Ill take it!
Thank you everyone who helped to inform me, i will be updating this thread after i do the mods