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Carburetor Boot Barbs vs In Carb Barbs for BS38 Carbs and Vacuum Petcocks

Discussion in 'The Garage' started by authenticnovelty, Nov 17, 2018.

  1. authenticnovelty

    authenticnovelty XS650 Enthusiast

    Hi All,

    After carefully studying the wealth of knowledge on this site all summer, I decided to create an account and open a thread hoping someone can point me in the right direction on my problem below. Any input would be greatly appreciated.

    This summer I picked up an early 1978 XS650E. The bike has dual vacuum petcocks in the tank, BS38 carburetors and carb boots with barbs to connect them.

    I need to replace the carb boots. Mike's XS has barbed carb boots, but they don't fit my bike. The barbs are drilled differently and do not clear the valve covers or fit the boot clamps (ordered and returned). I managed to find a pair of solid 40 year old original boots from a 1978 XS650 on eBay in very good condition, with the exception of a small 3/16th" single crack in the right boot. I coated it with Seal-All to try my luck and it has lasted me for the past 3 months. The crack has recently opened into a gap and often creates a fairly consistent lean mix once the bike is hot.

    I am again looking for a set of barbed boots which are compatible with the BS38 carbs and clear the factory clamps/Valve covers. I have found the JBM barbless boots and other barbed boots for the BS34 carbs, but I've had very little luck with my specific BS38+Barb combo. Does anybody have any recommendations? I am trying to restore/keep the bike factory and would prefer not to change the petcocks or air filters/add spacers. I've seen a post referring to drilling barbs into new smooth boots. Is this the only method left?

    Alternatively, could yamabond, threebond or similar be good to use on the single crack in the boot? I'm assuming not great inside due to gasoline exposure.

    Another thought... In the end of the carb guide, I see mention of adding a threaded nipple to the side of each carb for syncing. Does anybody know if it would be sufficient to thread in a set of these additional nipples for the vacuum petcocks to go directly into the carbs and just buy standard non-barb carb boots?

    Again, any input is greatly appreciated. Please also feel free to point to any existing posts, in case I have missed.

    Last edited: Nov 19, 2018
  2. grizld1

    grizld1 Grumpy old man Top Contributor

    Welcome! I suspect there's going to be quite a range of views on this subject, but here's my 2 cents' worth.

    IMO your best bet for boots is Tour Max (a K&L Distributing house brand). The boots are made in Japan by ARS, who made the original equipment. They're available from 650 Central and any shop with a K&L catalogue. They used to be offered with vacuum barbs, but it seems those were discontinued. IMO that's no loss; I've seen too many crankcases filled up with fuel to trust old vacuum petcocks. You could run lines from barbs in the synch. ports, but that would put the barbs and lines in a pretty vulnerable position. I use aftermarket manual petcocks. You could also ditch the vacuum line, run on Prime, use the Run position as a shutoff, and let your trip meter to tell you when to fuel, instead of running the tank down until you have to hit reserve.
  3. Brassneck

    Brassneck XS650 Guru

    +1 on Tourmax. I also found these that I was going to buy & test out when the time came...however I haven't had the need yet, so I can't say how they will fit compared to OEM: https://www.amazon.com/gp/product/B0149KM1M6/ref=ox_sc_saved_title_1?smid=A1AQO2OVG2C492&psc=1

    The barbs are nice for sync/balancing the carbs for sure. You could probably tap the carb itself if you can't find boots that work...but wouldn't that defeat the idea of keeping it stock? And if that's not an issue...then the easiest route is to drop the stock vacuum petcocks and go manual petcocks and get boots without the barbs. Or if you get the ones I posted and they too don't fit, like Mike's, perhaps flip them over/use on opposite sides, so the barbs face downward? Just a thought.
  4. mrtwowheel

    mrtwowheel Honda Etched On Brain Top Contributor

    I'm all for ditching the vacuum petcocks. On other forums they have earned the name SOS (son of satan ). You'd be convinced of this too if you saw one or two cylinders chugging away and the other cylinder/s pumping raw fuel in and out of the other cylinder/s from a ruptured diaphragm in the petcock. kinda like the shuttle explosion. Gonna trust a 40 year old piece of rubber to isolate raw fuel from spark and combustion, or even any piece of rubber that thin?

  5. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

    2 layers (diaphragms), just say'n and still using. With the occasional failure. :mad:
    mrtwowheel likes this.
  6. lakeview

    lakeview XS650 Guru Top Contributor XS650.com Supporter

    Fredintoon had a way of modding the vacuum petcocks to make a positive shutoff which involved grinding off the stop in the plate and shortening the lever so it could go to 12 o'clock. That would shut off the petcock for parking purposes.
  7. grizld1

    grizld1 Grumpy old man Top Contributor

    SOS? For many years I've offered this definition, Scott. Vacuum petcock: A device designed in Hell to Satan's specifications with a secondary function of filling crankcases up with fuel, and a primary function of driving motorcycle owners to acts of rage and despair conducing to the perdition of their eternal souls.
    Last edited: Nov 18, 2018
  8. joebgd

    joebgd XS650 Addict

    Uh ooh. Dare I say I have an 80 and never had an issue w vacuumed petcok. A few times on kick a backfire would blow the vacuum barb cap and or hose off. That hasn't happened in years too. I did put a vacume y coupling in so now both carbs are on the petcok instead of just one and one barb caped.
  9. authenticnovelty

    authenticnovelty XS650 Enthusiast

    Thank you all so much for the input. Part of my motivation for keeping the vacuum petcocks is that I actually just cleaned and rebuilt them with new seals when I bought the bike this summer. Trying to avoid all new petcocks, boots and in tank filters. If i do decide to add manual petcocks to my shopping list, what suppliers are people recommending? I see Mike's XS has some, but I know users here have varying opinions on what to get and not get from what retailers.

    I previously saw the suggested carb boots on amazon. Looking very closely, I believe they are the same supplier as Mike's XS. It's very subtle, but the listing photograph show's about 1/4" shift in the barb for the right carb and the angle is more vertical vs the left carb boot, which was the issue with the ones I previously ordered. Strangely, the left barb was positioned fine on the set I received. The other two issues are that even if mounted upside down, the metal casing that goes over the boot doesn't align with the offset barb and the alignment notch in the top of the rubber won't match the carbs when upside down.

    I recently found this set of barbed boots and emailed retailer, as they don't list which carbs or model years they are compatible with. Keeping my fingers crossed and will report my findings in case useful for anyone else: http://www.nichecycle.com/ncs/categ...-carburetor-flange-set-left-right-by-ncs.html

    I take it the option of putting some liquid gasket sealer in the boot is officially frowned upon? I'm hesitant to use hardening epoxy, for fear it may break loose and go into the engine.

    I've looked more closely at the option of barbs from 650 central directly on the carbs and it appears that the throttle cable will interfere with the nipple threads on the side of left carb at the last 1/4" of the butterfly opening path. Can't say I've really ever pushed the bike full throttle, but not fond of obstructions.
  10. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    I've had good luck bonding rubber stuff with Gorilla super glue, impact tough formula. It has rubberized plasticizers, and will flex a bit, making the bond less brittle.

    I used it to bond cracks in my instrument damper. It even survived the "rubber softening" procedure.

    Post #14.

    Of course, you'll have to be the judge if it works for your boot "bandaid fix...
    Last edited: Nov 18, 2018
    authenticnovelty likes this.
  11. Oddjob

    Oddjob adsgads

    Hi, I too had the same issues with Mikes XS boot fitment on the right side … to make it work I ended up shortening the barb by about 10-12mm or so… you can shorten it, one of two ways… if you don’t care about the flare on the end then you can simply hacksaw the end off… I decided to make life more complicated by driving the barb out from the inside using a 1/8” drift… shortening it by 10-12mm… and then pressing it back in… keep in mind that it is a press fit with the steel plate/flange that is “inside” of the boot, so it’s not as simple as trying to pull out the barb with pliers, or something like that…

    Of course, I had to do the same to the left side although it seemed to clear the valve cover nut as provided…

    What can I say… I’m not a big fan of this part, but there are not too many options out there. Mikes is weird that way… I’m sure that they must have received complaints from others, but they just don’t’ seem to care…

    Anyhow this is the right side with the shortened barb… just in case you decide to use Mikes or something similar again.

    authenticnovelty likes this.
  12. authenticnovelty

    authenticnovelty XS650 Enthusiast

    Thanks for sharing Oddjob. Beautifully executed. Can you elaborate on "1/8" drift" is that basically a steel punch? Did you use any specific glue to secure the barb when back in? Also, any issues with mounting the boots without the metal shroud?
  13. 5twins

    5twins XS650 Guru Top Contributor

    If you're still running the airboxes, leaving the metal shrouds off may be OK. If you have pods, you'll need the shrouds for added support or the boots will split. Like you, I had difficulty finding barbed manifolds for my '78. I had to go with the '74-'77 no-barb version and I then proceeded to transfer the barbs from my old manifolds to the new ones. I drilled slightly undersized holes in the new ones and pressed the old barbs in with some Yamabond on them to aid in sealing. They've been on there and working fine since '05.

    I did this so long ago that some of the details escape me now. I think I used a 3/16" drill bit but you would have to measure the barb diameter to be sure. The whole reason I replaced the manifolds in the first place was because one barb had come loose. It pulled right out with the vacuum hose when I tried to remove it. That meant I only had to extract one from the old manifolds. I "pressed" it out somehow, using a nut and bolt stack spanning across the inside of the manifold. But like I said, the exact details escape me now.

    You're right, the threaded barb can't be left in the left carb full time, it will interfere with the throttle cable and cable arm lift. It can only be used temporarily for syncing. Basically, you do your syncing at idle so cable operation and lever lift aren't a concern. But it may be possible to power both petcocks off just the right carb. Run a single line from there to a "T" and then to both petcocks.


    Last edited: Nov 19, 2018
    lakeview likes this.
  14. Oddjob

    Oddjob adsgads

    Hi, now that I think about it the punch (drift) was probably closer to 3/16in ie, just smaller than the base of the barb... to remove, I drove the punch from the inside while supporting the boot on top of a vise that was open enough (6mm or so) to let other side of the barb slide out... to install I drove the modified barb into the boot while supporting the boot on a pipe that fit snuggly on the ID... I did not use glue as both removal and install required considerable force...

    If I had a metal shroud I would have used it for the extra support... I’ve heard from others that if might fatigue the boot with time causing cracks if you don’t have it... I have the same carb set with the OEM boot and shroud on the bobber project and in comparison these feel a bit flimsy...

    Edit: “others” being 5Twins...
    Last edited: Nov 19, 2018
  15. authenticnovelty

    authenticnovelty XS650 Enthusiast

    Thanks 5twins & Oddjob for the elaborate details. I've found several threads regarding drilling and removing barbs but these posts clarify ideas and options significantly. Is Yamabond 4 the standard variety recommended for this task? I see Yamabond mentioned often, but usually without a number attached.

    I do have the original air boxes/filters and plan to keep them for a while. I'd still like to keep the metal shrouds for additional support though. It's such a shame, both barbs were loose in my original boots and i threw them out in a street garbage can when I got the Mike's XS replacements, assuming the barb issue was a one-off defect. Aside from burnt out bulbs, those boots are literally the only items I did not keep from the bike as I've replaced worn out parts.

    Out of curiosity does anybody casually know the outer diameter of the "spigot" on the BS38 that goes into the carb boots? I just spoke with the Niche Cycle Supply regarding their barbed boots and they don't seem to know the compatible bike year/carburetors or Yamaha OEM number the part is replacing. All they know is they fit a "spigot" with a 45mm outer diameter. I think it's safe to assume they are intended for the special with BS34carbs, not standard, but still keeping the hope alive. I can take a look with a caliper later today and report back, but figured worth asking just in case.

    For general BS38 reference, I'm attaching a previous xs650 post with the rear BS38 air box "spigot" measurement, in case anybody in the future comes across this thread and finds additional use for it.

  16. 5twins

    5twins XS650 Guru Top Contributor

    It looks like those Niche manifolds may fit the BS38s. Their spigot O.D. is about 47mm. The BS34s are much smaller, about 42mm.
  17. 5twins

    5twins XS650 Guru Top Contributor

    Let me also caution you against using the thin paper gaskets often supplied with aftermarket manifolds. You want an original thick type as shown in my pics. I think that besides sealing better, they were used to help isolate the carb and manifold from engine heat.
    gggGary and authenticnovelty like this.
  18. authenticnovelty

    authenticnovelty XS650 Enthusiast

    Thanks 5twins. I've attached a photo of my measurement on the boot spigot (which matches yours) for visual reference in the thread. I also received a response today from another rep at Niche Cycle Parts who handles the classic bike parts and had a wealth of hands-on knowledge with some additional ideas. Comparing my notes to his over the phone, their boots sound like a match for the BS38, but we couldn't quite confirm over the phone if the barb offset matches the aftermarket offset that we've all run into or if it's the actual Yamaha OEM spacing to fit the factory metal shrouds.

    In the name of science, I'm going to order a set of the Niche barbed boots to compare with my original 1978's and a set of the K&L barbless, then decide to just commit to manual petcocks and be over with or continue with vacuum pending barb results. In the mean time I filled the engorged boot crack with the Gorilla super glue TwoManyXS1Bs suggested to dry overnight while I had the carbs out.

    Will report back with my results soon.

    Last edited: Nov 19, 2018
    TwoManyXS1Bs likes this.
  19. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

    Also in the spirit of adding to thread value I have good success with two part plastic bumper epoxy, it dries flexible and really sticks to parts.
    Bondo 806 Easy Finish Epoxy Bumper Repair
  20. authenticnovelty

    authenticnovelty XS650 Enthusiast

    I got both sets of carb boots this weekend. Unfortunately, the barbed boots from Niche are identical to Mike's XS. Going to have to return them. I've went the route grizld1 suggested: using the tourmax, putting caps on the vacuum barbs of the petcocks and running on prime for now, as I work through other priorities on the bike. I've run out of patience with trying to make various forms of vacuum barbs work/seal properly. Now I am currently noticing about 400RPM worth of very gradual lean/rich drift on the right carb over a longer ride of maybe an hour in the city after warming up. Waiting on OEM boot gaskets at the moment. Will have to check for new/unexpected air leaks before/during gasket swap. Aside from that, it's finally consistent and feels great to ride. Thanks everyone for trying to help trouble shoot supplier options and a offering supplemental advice!
    grizld1 and gggGary like this.

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