1979 Carb Holder with Vacuum Barbs?

[LikeyMeYommy]

Hey Guys, Can't find a carb holder with vacuum barbs for my stock 79 XS650F (special). If I'm removing my airbox and using an air filter pod, can I use these?

https://www.mikesxs.net/yamaha-xs65...bs38-oem-447-13555-01-00-447-13565-01-00.html

Surprised MikesXS doesn't seem to have ANY carb holders for a 1979.

I did see on the carbguide.pdf in Tech (awesome) that vacuum barbs can be ordered from 650Central and installed in the boots. At this point, I can't even find a 79 standard boot?

Any suggestions??? What am I missing?

Thanks!

 

[jetmechmarty]

From here:
http://jbmindustries.com/HOLDERS.html

https://www.georgefixs.com/new-74-7...ers-intake-manifold-boots-gaskets-bs38-carbs/ I use this vendor, but these also have no barbs. I believe these are ARS.

With barbs:
https://www.z1enterprises.com/yamah...huAkL4U6nbFZfrEAIv3RcjOgTzrm-OoxoCeaIQAvD_BwE

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.

 

[hooser]

Email me at gary@hoosracing.com I have them,

 

[LikeyMeYommy]

 

[gggGary]

Yup been there done that, It's not easy to come up with an adapter that doesn't interfere with the throttle lever.

 

[grizld1]

The problem with JBM boots is not weakness of the plate but incompatibility with metal support shrouds. I tried a pair a few years back with a pair of Mikuni
TM36/68 pumpers that were a few grams heftier than a pair of BS 38s. After a couple of thousand miles the end of the spigot opened a split in the boot--exactly what the OE metal shroud is there to prevent.

 

[grizld1]

The pic shows the late BS38 with tapped holes for synch barbs. Get the right screw-in barbs and you're good to go. Pro-Flow makes nice ones in brass. The setup isn't made to use a permanent adapter and synch procedures don't involve whacking the the throttle wide open. Reason: the smaller the throttle opening, the larger the error in relation. Differences fade as the throttles open and the difference becomes a lower portion of the opening. If you want to use a vacuum petcock, IIRC you can install a permanent barb on the right. On my old F model one of the first thing I did was to convert to manual petcocks from Mike's XS, back in the day when he sent paper catalogues and customers ordered by phone. There are plenty of kits and adapters out there. Mike's XS and I think Heiden Tuning sell manual replacements that used to be and likely still are excellent. For others the drill isn't bolt on and go. You'd be well advised to block off one side and run a petcock on the other. You'd lose very little range. I checked this with the tank level. A single petcock will leave only 4 oz. of fuel in the other side.

 

[LikeyMeYommy]

Thanks for the insight @grizld1. I purchased some non-barbed boots from 650Central and some threaded barbs (not sure if Pro-Flow but talked to the guy and he was well aware of what I'm trying to do and recommended these would work). Said the same thing about keeping the right permanent if I still had the vacuum-type petcock. Honestly, I'm not sure what I have. I have RES, ON, and PRI positions on mine and in the ON position it is really off??? In any case, I was considering new non-vacuum petcocks after I give the tank a paint job.

How do I link the two sides of the tank in order to reduce to one petcock? I'll see if I can find in XS650.comland...

 

[5twins]

You have the vacuum petcocks, I can tell by the lever positions you mentioned. There is no "OFF" position. If they are working correctly, "ON" and "RES" are effectively off positions. They should only flow fuel if a vacuum signal is present. The vacuum works a diaphragm on the back of the petcock that pulls a plunger open inside and allows fuel to flow. The "PRI" position stands for Prime. It bypasses the vacuum operated part and just flows normally. You use it mostly to refill the carbs quickly after they've been drained. I also use it to refill the carbs if the bike has sat for several weeks and fuel levels may have gotten low due to evaporation. You can run the bike with the petcocks on "PRI" if you have no way of feeding them a vacuum signal but just be aware that the "PRI" position runs off the "RES" stand pipe in the tank so when you run out of gas you will really be out with no back-up.

When I replaced the manifolds on my '78, I couldn't get the ones with the vacuum nipples so I bought the ones without them and simply installed some. I removed the vacuum nipples from some old manifolds, drilled holes in the new ones, and pressed them in with some Yamabond on them to seal them up. They've worked fine for many years now. I chose a drill bit size slightly smaller than the vacuum nipple tube O.D. so they needed to be pressed in. I added the Yamabond simply for insurance that they would seal.

 

[grizld1]

You have vacuum petcocks. Read more carefully: a single petcock will drain the tank down until the other side contains only 4 US ounces of fuel. How m,uch range does that lose you? Later XS650 tanks were made with only one petcock. The right side is solid. What does that tell you? I'm done on this thread.

 

[LikeyMeYommy]

You have the vacuum petcocks, I can tell by the lever positions you mentioned. There is no "OFF" position. If they are working correctly, "ON" and "RES" are effectively off positions. They should only flow fuel if a vacuum signal is present. The vacuum works a diaphragm on the back of the petcock that pulls a plunger open inside and allows fuel to flow. The "PRI" position stands for Prime. It bypasses the vacuum operated part and just flows normally. You use it mostly to refill the carbs quickly after they've been drained. I also use it to refill the carbs if the bike has sat for several weeks and fuel levels may have gotten low due to evaporation. You can run the bike with the petcocks on "PRI" if you have no way of feeding them a vacuum signal but just be aware that the "PRI" position runs off the "RES" stand pipe in the tank so when you run out of gas you will really be out with no back-up.

@gggGary Read your thread on petcock rebuild. Fantastic/Appreciated!!

Thanks @5twins Very helpful in terms of additional info on theory of operation...

@GrumpyOldMan - It tells me the two sides of the tank are not independent and isolated from each other. I suppose the only benefit to having a petcock on each side was to use up the additional 4oz (<2 miles).