Help me ID these? and can they be tuned? Mikunis

1980 and 82 mikuni BS34 carbs BOTH need the rubber plugs to seal the pilot jets. otherwise it basically won't run because it won't pick up any fuel for the midrange.

The 80 carbs came with brass floats the 82 with foam floats. The 82 carbs were painted black and use a handle bar choke otherwise they are the same as the 80 carbs.
 
i have a 1979 motor with BS34's and am completely lost on tuning them. the carbs have velocity stacks....currently have 27.5 PJ and a 130 MJ and running straight back 1 3/4 pipes with no baffles. i also have a PAMCO installed.

left side idles o.k. however right side seems not to be firing...exhaust is cool not warm as other side.

Any help would be greatly appreciated.

WRMDOVR
 
I got a TM34 flatslide with 210 main Jet, needle set to lean, pilot jet seems good. Throttle feels Asymmetrical, as in 0-20 is rough. WOT is like a race bike. Is this jet low or High?
 
The VM slide carbs have I.D. numbers stamped there by the chokes. As far as I know, there are no numbers stamped on the BS vacuum carbs. We can I.D. them because we've studied them and know how they look. We know the little changes made through the years.

You may find one letter stamped on the bottom of the float bowl but that has nothing to do with the carb or carb set I.D. I'm really not sure what that letter means.
 
An excellent jetting compilation from threads here and on XS650 rider, by 2many xs1bs

MJ = Main Jet
PJ = Pilot Jet
NJ = Needle Jet (emulsion tube)
JN = Jet Needle
Slide = Cutaway number
_________________

Roy Fisk
Carb: VM34
MJ: 190-200
PJ: 22.5
NJ: P6
JN: 6DHS, 3rd slot
Slide: 2.0
Air jet: 2.0?
Air screw: 1.25- 1.75
Float height: 25mm
_________________

Richard, from the Aussie site
Carb: VM34
MJ: 180-190
PJ: 20-25
NJ: P5, P6
JN: 6F9, 3rd slot
Slide: 2.5
Air jet: Removed

Dwayne, from the Aussie site
Carb: VM34
MJ: 180
PJ: 25
NJ: P6
JN: 6F9
Slide: 2.5
Air jet: 2.0?

Bob Hart, from the Aussie site
Carb: VM34
MJ: 180
PJ: 27.5 - 32.5
NJ: P5, P6
JN: 6F9
Slide: 2.5
Air jet: Removed
_________________

HALCO (UK)
Carb: VM36
MJ: 220
PJ: 25
NJ: 159-Q2
JN: 6DH3
Slide: 2.5
Air jet: 2.0

BOB BERTAUT (VM36 CARB KIT)
Carb: VM36
MJ: 190
PJ: 22.5
NJ: 159-P6
JN: 6DP1
Slide: 2.5
Air jet: Removed
_________________

Yamaman
Carb: VM34 with Ramair pods, Triumph silencers ,Halco 1 1/2" pipes.
MJ: 185 - 190
PJ: 25
NJ: P6
JN: 6DH4, 3rd slot
Slide: 2.0
Air jet:
_________________

gggGary's Madness
Carb: VM38
MJ: 260 (220?)
PJ: 25
NJ: 166-P8
JN: 6DP1, 3rd slot
Slide: 1.5
Air jet: Removed.
Float valve: 3.3

gggGary's Pristine, never had gas in them yet.
Carb: VM34
MJ: 180
PJ: 25
NJ: 159-P6
JN: 6F9, 3rd slot
Slide: 2.5
Air jet: ?
Float valve 3.3

gggGary's Unknown
Carb: VM34
MJ: 260
PJ: 40
NJ: 247-Q2
JN: 6DH4, Top slot
Slide: 2.5
Air jet: ?
float valve 1.5
_________________

Grizld1's 700cc
Carb: VM36
MJ: 190
PJ: 22.5
NJ: 159-P5
JN: 6F9, 3rd slot
Slide: 2.5
Air jet: Removed
_________________

TwoManyXS1Bs 750cc Dragon
Carb: VM36 (Vintage 1975, opened to 37.5mm)
MJ: 270-280
PJ: 35
NJ: 159-Q5
JN: 6FJ6, 3rd slot
Slide: 3.8
Air jet: 2.0
_________________

Barncat Ported head, performance exhaust
Carb: VM36
MJ: 190
PJ: 25
NJ: 159-P6
JN: 6F9, 2nd slot
Slide: 2.5
Air jet: none
air/idle screws out 1-1/2 turns
Very smooth power delivery and pulls hard through the entire range.
 
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Weaselbeak posted up this jet size comparison

Keihin, Dynojet, Mikuni Jet Size Cross Reference

All Hole Diameters Are in Inches

Hole Dia"---Keihin # -- DynoJet # -- Mikuni #
0.0350---- 92.5--------- 92----------- 86.3
0.0360---- 95----------- 94----------- 88.1
0.0370---- 97.5--------- 96----------- 90
0.0380---- 100---------- 98----------- 91.9
0.0390---- 102.5------- 100---------- 93.8
0.0400---- 105--------- 102---------- 95.6
0.0410---- 107.5------- 104---------- 97.5
0.0420---- 110--------- 106---------- 99.4
0.0430---- 112.5------- 108--------- 101.3
0.0440---- 115--------- 110--------- 103.1
0.0450---- 117.5------- 112--------- 105
0.0460---- 120--------- 114--------- 106.9
0.0470---- 122.5------- 116--------- 108.8
0.0480---- 125--------- 118--------- 110.6
0.0490---- 127.5------- 120--------- 112.5
0.0500---- 130--------- 122--------- 114.4
0.0510---- 132.5------- 124--------- 116.3
0.0520---- 135--------- 126--------- 118.1
0.0530---- 137.5------- 128--------- 120
0.0540---- 140--------- 130--------- 121.9
0.0550---- 142.5------- 132--------- 123.8
0.0560---- 145--------- 134--------- 125.6
0.0570---- 147.5------- 136--------- 127.5
0.0580---- 150--------- 138--------- 129.4
0.0590---- 152.5------- 140--------- 131.3
0.0600---- 155--------- 142--------- 133.1
0.0610---- 157.5------- 144--------- 135
0.0620---- 160--------- 146--------- 136.9
0.0630---- 162.5------- 148--------- 138.8
0.0640---- 165--------- 150--------- 140.6
0.0650---- 167.5------- 152--------- 142.5
0.0660---- 170--------- 154--------- 144.4
0.0670---- 172.5------- 156--------- 146.3
0.0680---- 175--------- 158--------- 148.1
0.0690---- 177.5------- 160--------- 150
0.0700---- 180--------- 162--------- 151.9
0.0710---- 182.5------- 164--------- 153.8
0.0720---- 185--------- 166--------- 155.6
0.0730---- 187.5------- 168--------- 1575
0.0740---- 190--------- 170--------- 159.4
0.0750---- 192.5------- 172--------- 161.3
0.0760---- 195--------- 174--------- 163.1
0.0770---- 197.5------- 176--------- 165
0.0780---- 200--------- 178--------- 166.9
0.0790---- 202.5------- 180--------- 168.8
0.0800---- 205--------- 182--------- 170.6
0.0810---- 207.5------- 184--------- 172.5
0.0820---- 210--------- 186--------- 174.4
0.0830---- 212.5------- 188--------- 176.3
0.0840---- 215--------- 190--------- 178.1
0.0850---- 217.5------- 192--------- 180
0.0860---- 220--------- 194--------- 181.9
0.0870---- 222.5------- 196--------- 183.7
0.0880---- 225--------- 198--------- 185.6
0.0890---- 227.5------- 200--------- 187.5
 
An excellent jetting compilation from threads here and on XS650 rider, by 2many xs1bs

MJ = Main Jet
PJ = Pilot Jet
NJ = Needle Jet (emulsion tube)
JN = Jet Needle
Slide = Cutaway number
_________________

Roy Fisk
Carb: VM34
MJ: 190-200
PJ: 22.5
NJ: P6
JN: 6DHS, 3rd slot
Slide: 2.0
Air jet: 2.0?
Air screw: 1.25- 1.75
Float height: 25mm
_________________



Richard, from the Aussie site
Carb: VM34
MJ: 180-190
PJ: 20-25
NJ: P5, P6
JN: 6F9, 3rd slot
Slide: 2.5
Air jet: Removed

Dwayne, from the Aussie site
Carb: VM34
MJ: 180
PJ: 25
NJ: P6
JN: 6F9
Slide: 2.5
Air jet: 2.0?

Bob Hart, from the Aussie site
Carb: VM34
MJ: 180
PJ: 27.5 - 32.5
NJ: P5, P6
JN: 6F9
Slide: 2.5
Air jet: Removed
_________________

HALCO (UK)
Carb: VM36
MJ: 220
PJ: 25
NJ: 159-Q2
JN: 6DH3
Slide: 2.5
Air jet: 2.0

BOB BERTAUT (VM36 CARB KIT)
Carb: VM36
MJ: 190
PJ: 22.5
NJ: 159-P6
JN: 6DP1
Slide: 2.5
Air jet: Removed
_________________

Yamaman
Carb: VM34 with Ramair pods, Triumph silencers ,Halco 1 1/2" pipes.
MJ: 185 - 190
PJ: 25
NJ: P6
JN: 6DH4, 3rd slot
Slide: 2.0
Air jet:
_________________

gggGary's Madness
Carb: VM38
MJ: 260 (220?)
PJ: 25
NJ: 166-P8
JN: 6DP1, 3rd slot
Slide: 1.5
Air jet: Removed.
Float valve: 3.3

gggGary's Pristine, never had gas in them yet.
Carb: VM34
MJ: 180
PJ: 25
NJ: 159-P6
JN: 6F9, 3rd slot
Slide: 2.5
Air jet: ?
Float valve 3.3

gggGary's Unknown
Carb: VM34
MJ: 260
PJ: 40
NJ: 247-Q2
JN: 6DH4, Top slot
Slide: 2.5
Air jet: ?
float valve 1.5
_________________

Grizld1's 700cc
Carb: VM36
MJ: 190
PJ: 22.5
NJ: 159-P5
JN: 6F9, 3rd slot
Slide: 2.5
Air jet: Removed
_________________

TwoManyXS1Bs 750cc Dragon
Carb: VM36 (Vintage 1975, opened to 37.5mm)
MJ: 270-280
PJ: 35
NJ: 159-Q5
JN: 6FJ6, 3rd slot
Slide: 3.8
Air jet: 2.0
_________________

Credit where credit's Due...................Those Aussie site setups do not come from the Aussie site..........Read the thread i linked to where this info come from
 
Sure, I did it all myself! :redface:
It's a compendium from a 650 archive thread and at least one thread on here. Many authors, all sharing in the spirit of the 650 brotherhood. Skull brought the thread with most of the set ups to our attention. 2many did the clean up and organization. Kudo's to all mentioned or not.
 
Point i'm making is critical information has been left out and location is wrong on some..............Elevation and climate makes a difference to the set up so if that is left out.....................
 
Gary, so in your opinion is it worth it to move from the bs38 to the vm34? My bs38 carbs will need a total rebuild. If there are better characteristics in the VM carbs where throttle response is concerned it may be worth the couple hundred dollars for the change.
My experience with bikes so far are limited to 883 Sportsters. I had the stock CV on one bike and a Mikuni HSR42 on another. The Mikuni had way better throttle response and was easier to tune.
I appreciate any advice one way or another.
 
I'm a big fan of stock carbs, unless you have built a performance motor it's hard to beat a well fettled set of 78-79 BS38s. Heck I like BS34s too. Just sold a really nice set of BS34s maybe I'll try the set ninja carbs I got out in the shed next. But I'm also very happy with how the VM34s have run on madness this year put 3-4K miles on it. Want to try a set of Keihin pumpers someday also.
Guess the point is, if set up properly and tuned for your engine, altitude they all work pretty darned good.
PS if you are using CV carbs you need to keep big airboxes in front of them. CV's just don't like tiny air filter volume. There's a reason manufacturers go to such lengths making huge airboxes that squeeze every speck of room available into the box. A Ducati forum did some testing on one bike, a larger airbox from a previous model was worth 10 horsepower, Yamaha got similar results increasinging air box volume on the V4 Ventures.
 
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I've modded my seat frame so the factory airboxes are out of the question. I wonder if I could fabricate my own to fit in the remaining space. Or perhaps it's a good excuse to go ahead an get the new carbs.
 
Guys, those jet lists are nice, but they're not likely to be very helpful unless the user keeps a few things in mind. First: note the inverse relationship between NJ size and MJ size. Second: note the inverse relationship between slide cutaway and PJ size (smaller number=richer slide, richer slide forces leaner PJ, etc). And finally, understand that needle position directly impacts pilot circuit tuning: A change of 1 step will always force mix screw adjustment and will often force a PJ change. The pilot circuit never turns off, and the main circuit impacts the mix even at idle, through the slide cutaway.

The variation in those lists demonstrates something to keep firmly in mind. Carburetors have to maintain a usable fuel/air mix across a wide and shifting range of demands, and they have to do it with a few simple components. The most accurate jetting involves compromise. Bottom line: there are many combinations that work, there are some that work better, and there are some that don't work at all.

As far as jet lists go, treat them as possible starting points. Some guys take to tuning aftermarket carbs like fish to water, some guys get lucky, and some guys wind up wishing they'd never been tempted to fool with old motorcycles at all, let alone modify one. The best advice I can offer the beginner who wants to hang aftermarket carbies on his bike is first: Read some threads by others who've done the same, asking yourself if you have enough patience and frustration tolerance to enjoy the tuning job as a project. And second: Buy a responsibly baselined set of carbs from a reputable vendor who owns and knows the XS650 and offers tech support after the sale. In the USA, I can recommend Michael Morse of 650 Central and Gary Hoos of Hoos Racing.
 
X77S, Mikuni flat slide pumpers like the HSR42 are indeed a joy to tune; component effects are much better isolated than they are in early designs like the VM, which are touchier (in spite of being simpler). You should see an improvement in throttle response with well tuned VMs, but not as much of a difference as you've seen between a vacuum diaphragm carb and a pumper with flat slide and direct connection between twistgrip and slide.
 
Thanks Griz. Perhaps it's best if I just rebuild this set I have. I will look into what kind of air cleaner/ box I can make work if the Uni filters work decent I will probably go with that and be done with things.
 
As far as pod filters go, the long, straight foam UNIs work best on the stock CV carbs. I know from experience that the K&N pleated style pods don't work as well. You won't be able to tune the carbs perfectly with them. The bike will run, just not as good as it could. I finally have an airbox equipped 650 and truth be told, I don't see much difference compared to my other pod equipped one. Both run well and I'd be hard pressed to pick one over the other as far as performance goes. But, I haven't had my way yet with the carbs on the airbox bike, lol. They're still jetted all stock and being BS34s, I know they're a tad lean. Maybe once I richen them up a little bit, my airbox opinion will change. At the moment, the only airbox "plus" I'll concede to is rain riding, of course they're better for that.
 
I've used Outerwears rain covers with K&N filters on Mikuni VM round slide and TM flat slide 4-stroke pumper carbs, and they do a great job of keeping the filters dry and breathing freely. The covers create very little restriction. Outerwears will make covers for filters of any dimensions, and I've often wondered how they'd work with Unis.
 
The only issue I've experienced with my pods in the rain is when I come to a stop. The bike can run rough and even stall if they're really wet or sucking in water because it's down pouring. At speed, running down the road, they seem OK in the rain. I don't do much rain riding so it's not an issue I have to deal with very often. What I enjoy and take advantage of much more often is the ease of access the pods provide.
 
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