Pilot jet designation?

[motoman]

My 81Venturer does have the stock pilots in it(42.5). My question is: what is the CORRECT letter designation to determine if off-brand kits were ever used in these carbs? Magnifing glass works number reading on these, but can't quite make out letter designation prefix. Visually, two PAIRS of holes opposite side of each side other/two holes, one each side centered between and opposite paired holes. Is this the correct configuration pilots for the later 81 carbs? May or may not explain the rich cond. while in idle circuit......least the 1200-4000rpm range........Also became "needy" in the timing advance area also, specificly vacuum advance. Found advance assembly freely moved, but not freely enough and vacuum can would not rotate assembly, cleaned untill it spun like a lazy-susan. No more "loping" in the cruising rpm range and snaps up revs quickly(Thanks 3Phase). Just wantin' to get this sled back hummin' down the road like it always used to.........bad karma as a rally host if scoot isn't cooperating......to a "T".

[natemoen]

The style jet is BS30/96. That also is the correct hole configuration.

[motoman]

Thanks Natemoen...........dern, hopin they'ed be wrong configuration...........back to head scratchin' as pri./sec. ign. sources and valve-train all good to go.........seems when they become 30 they become "needy"............................just cause they can.

[bikerphil]

Motoman, don't know how many miles on your 81, but the slide needles and emulsion tubes do wear and will cause a rich condition like you are describing. It is easy to see the wear on the slide needles. I replaced my needles at about 90K and it helped tremendously. I can't find any emulsion tubes for my early carbs though.

[motoman]

Thanks bikerphil.......was trying to avoid that untill a closer look deemed necessary. Today , pulled carbs back off, decideing one way or another was going to solve its "neediness". What I found was that I had wished I'd never sold this scoot after ten yrs. of ownership from new. Dern PO's!...........a crap shot gettin it back runnin' correctly, specially some fourteen yrs. later let alone getting back the same scoot. Second thing found upon closer examination other than some three years ago finding 105mains in it and changing them to 110's, was actually removing the pilots and air jets rather than just blow carb clean to make sure all is open. Three of the four are correct 185's all else being stock original. The fourth air jet is a 105.....WTF. On top of that, the designation looks to be K&L.........eeekkkk. Next, removed the pilot jets. Looks to be correct with the paired holes opposite each other and the two opposite single holes and marked 42.5, again correct. With magnifying glass, can't quite make out designation before the size number.............so, even though visually they may look correct, should they be suspect to? Lastly, what has led me to this point is having to set air-mix screws some 4-41/2 turns out, no matter what changes are made to float levels or main jetting. A minute amount of fuel apparently is drawn through mains while running in the idle circuit, even on these later model carbs, which would maybe explain someones logic installing 105 mains to get a clean burn in the idle circuit. With the replaced motor of 32k, model correct and 83 in production numbers behind original, ran it making no carb inspection for three years this way. Ran smooth, a little "mushy"/ slower than I remembered a couple decades ago and consistantly got 38-42mpg. Gonna clarify my suspitions first of week comparing Mikuni's with what I got, or just replace with new to eliminate any tuning/running suspitions jetting associated. I'll report back on this thread to my findings.

[natemoen]

If the pilots have the 2-1-2-1 hole setup then they are correct. The other styles have either 8 joles or no holes.

[3Phase]

Brant, I was hoping the pilot jets had been changed to 45 but finding a mix-n-match air jet isn't a bad day's work, either. What the heck happened there?

Apropos of almost nothing until you check the emulsion tubes and needles for wear: I wonder if the emulsion tubes can be brazed closed at the top then drilled to the correct size. Of course if Mikuni did some kind of weird Mikuni-thing to the shape of the outlet instead of making it a straight hole that would completely toast a rare part instead of repairing it.

I know I saw a picture of an XS11 emulsion tube sawn in half but I can't remember where I saw it or how it was shaped.

[motoman]

Scott, I got a fairly good idea who had there fingers fumbling around at best with the carbs. Yup, where we got your CCT. That's where the bike was bought from when it came to Junction from Phoenix. after I sold it while living in GlenwoodSprings,CO. The head "wrench" whom I've known through there for some 18yrs. would like to think he is a carb guru. Likely happened there before sold. If it were done while in Phoenix some six years, and having the 105mains, doubt if it would have have survived the diet........collapsed rings,scored cyls. over time,collapsed skirts, and finially holed pistons. By 80 and definitely 81 these were in lean-burn mode to meet emissions as it was with the changed cam profile and valving, along with carb re-designing and function. Going to make sure these carbs have or get all the correct Mikuni jets in it, re-set floats to just 1mm under the 3mm wet RUNNING check which will put them at 24mm instead of the "compensating" 26mm I have them at. Manual specs. being of sea-level settings is reason for the slight differences front stock........that's what we do up here. Actually, applies to 4-5000ft. elev. and above. Instead of 110's across, since I have them gonna go with 112's center and 110's ouside cyls. just for grins. Being stock when new and run 85percent of time at 6500ft and to above 10,000ftelev., did notice at 7500 and above would "load" up a bit if pulled down any length of time on steep grades under 3500rpm......downshift cleared out unburnt fuel. I'll first get this "is it or is it not K&L demons" sorted out.

[CaptonZap]

Howdy, Motoman,
You mentioned that your vacuum advance was being a little squirrely. Do you run any additional advance to compensate for altitude?


See you in Durango, CZ

[motoman]

Interesting you mention that CZ. Since it has the fixed(non slotted) assembly it is what it is. So the answer is no. Interesingly though, my original 81 motor, which was only 83 in production numbers earlier than the Venturer motor now in it has the slotted assembly with advance/retard degreed plate. The 3 screws have the tan epoxy on them, but that could easily be breached. Also this bike came from factory with the gold diaphragm tops. Even with its production date of June '80, tells me by then with the end of the XS11 series coming to an end and introduction of the XJ series forthcoming may explain the carbs having the MNS gold tops, along with a couple other sutle differeces I have not seen on other 81 Venturers. Back to the advance, I did notice with vacuum can removed and a slight rotation manually (advancing) of assembly corresponding coming off idle, it responded a bit quicker and smoother initially off idle. IIRC, quite some time back Ivan removed the epoxy plug and found the vacuum can to be adjustable, so I'm sure it could be lightened up a bit to compensate for slower and less total vacuum draw at higer elevations. As you know, on our old school vehicles, you advanced the static timing one degree for every 2000ft.of elevation from what sea-level specs. where. Don't do it and mash your foot in the throttle, you'd get some serious knock/pre-ignition as you know. So if someone wanted to experiment a bit that lives and rides at 5000ft. and above, can see where lightening up the draw needed to initially start movement of advance mechanism at a bit lower rpm would definitely improve off idle response and likely improve economy substansually if constantly ridden at above 4-5000ft.elev..........same as the automotive world and the high performace end of it I was involved with during the muscle-car era. Like I said in an earlier thread, this bike, litterally rode off the showroom floor new in Durango(6512elev.) and rode ten years with not so much as a sync ever done(didn't know it was needed), ran flawlessly that whole time. Just put gas in it, changed oil every 2000miles, cam-chain adjustment whenever idle fluxuated some and would'nt hold dead-on 1100rpm, changed plugs every 10,000miles........bout as trouble free as you could get back then. Hope that brought up some points to stew on for a bit.

[motoman]

I believe between 3Phase and I, the carbs mid-range issue is mostly solved. Found the carbs to have the Special needles(5GZ16) instead of the Standard needles(5IE26). Again these are the late model carbs. This would explain finding the mains to be 105's before I changed to 110's some 3yrs.ago. trying to resolve the lean cond. At this point, the way they are set-up with the Special needles, going back with 110's or 107.5's center cyl. and the 105's or 107.5's outer cyl. Should put it back at least running smoothly in the mid-range even if it is a bit "mushy" on the upper end. Majority of the time is running in the idlecircuit anywys.......and occassional Interstate in the mains. Did notice back when the 105's were in, it ran extremely well 8000ft. and above, even with the unknowing incorrect needles. Was also running a consistant 40-42mpg@65-70mph being on the lean side. IMO got away with it due to always running it at 5000ft. and above, even several runs to SaltLake and back which is 650mi. round trip. For now, also have to live with idle screws runnin' 4turns out untill I come across correct needles. If anyone here has a set of the Standard needles for the later carbs, or............drumroll..........78-79carb needles(yes, they'll work well also verified by 3Phase's l--o--n--g haul through Canada down here to G.Junction last fall.), would be able to set these carbs back up properly as they should be! Meanwhile, wanna give a big THANKS here for the help from 3Phase, Ray, natemoen,bikerphil and all who's had input with this issue. Goes to show an ole' seasoned dog CAN learn new tricks!

[natemoen]

Heck I didn't even realize the specials and standards had different needles....

[motoman]

Heck I didn't even realize the specials and standards had different needles....
__________________
....and different stock jetting........lest for 81model anyways. The chart in the back of Clymers is BS......as is alot of the rest of it, but can work in a pinch to get ya going......

[3Phase]

Heck I didn't even realize the specials and standards had different needles....

Nate, the '80/'81 Special needles are still available in some carburetor rebuild kits, the Standards are not. The '80/'81 Standards use a 5IZ7 jet needle and the Specials use a 5GL16.

The length, taper and shape of the tip is described by the needle jet numbers and letters. The jet needle controls the fuel fuel supplied to the needle jet (emulsion tube) by the main jet in addition to the fuel supplied by the pilot jets during low and midrange RPM.

What that means for normal people that don't intuitively understand Mikuni-speak for their jet needles and can immediately picture their shapes just by looking at the numbers and letters is:

'80/'81 Standard needles have a steep taper with a sharp tip and they're a little shorter than the '78/'79 needles.

'80/81 Special needles are even shorter still, with a steeper taper and slightly sharper tip than the '80/'81 Standard needles.


The Standard needles supply less fuel initially from the main jets with a slower transition to the main jets at higher RPM.

The Special needles supply more fuel initially than the Standards and the transition to the main jets is more rapid and occurs at lower RPM.


Along with the different needles, the main jets in the Specials and Standards are different sizes. The Specials have 110 main jets and the Standards have staggered 115/120 main jets so:

If you try to use 110 jets with the longer Standard needles there won't be quite enough fuel during low and midrange operation. The engine will run hot, lean and mean until the slides open up, then it will still be a little lean at high speeds.

If you try to use 115/120 jets with the shorter Special needles there will be a little too much fuel during low and midrange operation. The engine will run soggy, slow and rich until the slides open up and the engine is running fast enough to use the fuel supplied by the main jets and your grin is moved back to somewhere behind your ears.

[motoman]

After having conversation with Scott and Ray, and a little decifering on my own, since 81Standard metering rods are basicly among unobtanium, gonna set them up as 81Special carbs that they are at this point with the Special metering rods. Figure at some point in time while gone from my ownership the carbs got changed keeping the gold tops aboard as it came when I bought it new. Doubtful if anyone went to the extent of changing metering rods, specially if done at a dealer/shop. So........gonna set them back up as bar-hoppin,sling-shot 81Special carbs that they were, since the metering rods in them are gonna dictate that at this point. Don't know for certain with the earlier year models, but do know for certain that the 81Venturer(the ONLY Standardmodel U.S.) had several sutle differences including carb set-up, frame configuration differences(verified by CrazySteve on this sight) and many other sutle differences not noticed untill one starts any changes or mods. As Crazy Steve stated a while back, the Venturer was a one year one of a kind animal in more ways than one would think. I DO know the Canadian version of the 81Venturer still had the five position metering rods, but not the same style rods as the early carbs. With that I can see the Canadian version for sure and possibly the other over-seas versions have enough differences that tuning and adjustments CAN'T be made based on what other folks in other parts of the world are doing on the same year model......lest not on 81's for sure. The XJ model is again a totally different set up as far as jetting, timing, and I suspect valve timing if one were to degree the cams for lift and rate of lift associated with timing ect. than the XS is anyways. By 1980, suspect this mostly had to do with meeting stricter emission standards depending on where they were being imported to. Please, any and all feel free to chime in with there thoughts. Any and all information or thoughts are always good to ponder over during problem solving and the decision process, whether they are totally correct or not. That's how we all learn and pass it along to other unknowing victims associated with the XS insanity. I say insanity, as no one I know of in a NORMAL state of mind would jump on one of these now 30+ year old scoot and ride some 3,000 miles one way across the U.S..............then turn around and repeat..........and then go through the same processs repeatedly........nuts I'm tellin'ya......but way fun and an adventure..........that's what it's all about anyways........ride,,,,,,then continue repeating........whatever it takes to keep that grin, right?