VM34

[Hairball27]

I'm sure there has been a thread on this, but so far have not read any that have asserted info on jetting specs with 2.5 slide , does or does not work properly with a 2.5 cut slide, this is what i have in these new carbs. I would like to jet it for a standard 650 street set up. thanks in advance.

 

[grizld1]

Go here: www.amckayltd.com/vm34-36.pdf. A 2.5 or 2.0 slide both will work fine in a VM34 on an XS650 , you just need to select a richer pilot jet with the 2.5; from sea level to 800 feet or so, usually 22.5 or 25. You'll find more by clicking the Tech button at the top of the page.

 

[grizld1]

These numbers are not "jetting specs." They are a baseline setup that gets you close to where you need to be. There is no "spec" jetting for aftermarket carburetors, most of which will be mounted on machines with modified engines and/or exhaust systems, each of which will have its own requirements. The tuner has to know how to understand what the engine is trying to tell him. If you don't own a copy of the Sudco Mikuni Tuning Manual, you may want to buy one. Good luck.

Slide: 2.5. PJ: 22.5 to 25. NJ: Series 159, P-5 or P-6. Needle: 6F9. MJ: 180 to 190. Main Air Jet: Remove.

 

[AUTOMAN]

btw- cut aways are not in MM's as the article says.

"3. cutaway height (richest is 1.5, then 2.0, 2.5, 3.0, 3.5 leanest; size is arc height in millimeters at center)"


cliff

 

[toglhot]

I got half a dozen main jets with my VMs, but no extra needles or pilot jets, I believe a 2.5 slide is supplied with the conversion kits.. Haven't looked at the the main yet, but the needles work well on the third groove, pilot screw is out a bit farther than I'd like but it runs well. I run open pipes at the moment and pods, this makes a difference to jetting as does altitude. Mikunioz have a jetting guide on their site if you need it, but jetting is quite easy without, as long as you understand the function of each system on slide carbs.

 

[grizld1]

Right, Automan, I accepted the comments from "panic" without careful reading, and the whole of that quoted material is erroneous. He is in error regarding tuning adjustments for slide changes in addition to the slide spec kerfluffle. He is also in error regarding the air jet and its function. In VM34 and 36 carbs the tunable AJ is in the main circuit and has nothing at all to do with off idle transition. Its function is to prevent excessive aeration and resulting lean mix at the atomizer (needle jet) at the sort of high rpms that our motors will never see, which is why we remove it. Sadly, I mistook his confidence for competence. I'd edit that material if I could, but it's out of my hands.

 

[grizld1]

Regarding kits and jetting, the Sudco recipe uses a 2.0 slide with 15 or 17.5 pilot jet, which is one reason that Sudco kit carbs are more expensive than others; the slide is a pricy piece of brass. The 2.5 slide is the one that comes in the carb from Mikuni, and most users are happy with it if the right PJs are installed.

 

[AUTOMAN]

Last time I know sudco does not have Mikuni brass.
So even that source of info is suspect.

cliff

 

[grizld1]

Last I knew, Sudco was one of two distributors for Mikuni America, the other being Carb Parts Warehouse, retailers got their Mikuni carbs and brass from one or the other. and Sudco's current pdf catalogue continues to list Mikuni carbs and brass. If you know something to the contrary, please back up your assertion. And what source is it that you regard as "suspect?" Sudco? They've only been selling carbs and kits set up for the XS650 for around 40 years, so that claim is also going to need more than bald assertion to be credible. If you can contribute help for folks trying to tune VMs for the XS650, please start writing, I'm sure admin would love to have more material in the Tech section. If your purpose is to throw shade--well, have at it.

 

[drgonzo]

My well abused stock XS2 engine seems happy here at 600Ft. above sea level with:
Slide: 2.5. PJ: 30. NJ: Series 159, P-5. Needle: 6DP1. MJ: 175
It may not be perfectly dialed in but it's very close.
YMMV

 

[grizld1]

Rome, GA, Doc? That's my old daddy's birth place. I have kin among the Russells, Whittenburgs, and Gattises there, but haven't been in touch for many, many years.

You've given a good example of the fact that different motors ask for different things. I'm at around 800 ft. above sea level, so I'd guess that our running-around elevation averages out about the same. But on the XS650s that I've set up with VMs, with the same 2.5 slide and P-5 NJ, I'd have had a rich mess at idle even with the mix screw leaned out to the max, and that was the case with a 6DP1 needle on the middle notch as well as the 6F9 I came to prefer.

Looks like you have a fine machine, Doc. Congrats--keep the shiny side up!

 

[drgonzo]

Yup Rome, GA. Griz, I am running these exactly as they came from Gary Hoos. 1 turn out on the mixture screws. Lot's of ways to skin a cat I reckon.

 

[grizld1]

I don't know what Gary does to make that #30 behave, but if it works, it works! I usually wind up around 1/2 to 3/4 turn out with a 22.5 PJ, and most guys wind up with a 25 at similar elevation. If the motor says it's happy, that testimony trumps any and all recipes!

 

[johne67]

Go here: www.amckayltd.com/vm34-36.pdf. A 2.5 or 2.0 slide both will work fine in a VM34 on an XS650 , you just need to select a richer pilot jet with the 2.5; from sea level to 800 feet or so, usually 22.5 or 25. You'll find more by clicking the Tech button at the top of the page.

Kind of reviving an old thread here, but this link isn't working. I saw this link throughout various other threads and I'd really like to take a look at it. It takes me to a "godaddy" page every time I try it.

 

[jpdevol]

Here ya go

 

[jpdevol]

BTW, @grizld1 is Dick Russell (RIP) and wrote that guide. Many of us are enroute (or about to be) to the Ozarks for the
https://www.xs650.com/threads/2023-...e-yamaha-650-society.63539/page-7#post-792816

 

[willis]

Saw the attached and thought this might be an appropriate place to share.

https://www.bikeexif.com/rebuilding-mikuni-round-slide-carburetor