Thanks for the reply. After some study, I decided that yes, you should use a gasket. The JBM boot is exactly the same thickness as the stock boot. If you don't use a gasket, then the carb is too close to the engine -- you need the gasket to get the correct spacing as intended by the Yamaha engineers.
The intake gaskets are about 3/32" when compressed, almost 1/8".
No, I don't know if that makes a difference, but why take chances?
From what I gather from this forum, moving the carb closer to the manifold improves top end but decreases low end power, and vice-versa for moving the carb away from the manifold. I need low end power, so I don't want the carb any closer to the manifold then the engineers intended.
The original gasket is quite thick and besides sealing, may have been designed to help insulate the manifolds from engine heat and vibration. I think I'd be inclined to use them. I put a narrow ring of sealer on the gasket between it and the manifold so it comes off with the boot any time I remove it. I don't use sealer on the engine side. I don't know if you've ever had the pleasure of cleaning a cemented intake gasket off the motor but take it from me, it's no fun, lol.
I lost a vacuum cap my own fault put a new mikes cap last summ er should have replaced and forgot. Due to the fact the the JBM boots uses the 1/8 tube ID small hole the ride home wasn"t all that bad some backfire. the bike ran ok considering. Bought a box of 25 from Fastenal $ 8.16 part no 162602 not than I will ever need them. autoparts store out they wanted close $4.00 pack of 5 .They are not going to come off a little hard to get all the way on used a screwdriver last half. They don't pry off easy.I doubt I would have been riding anywhere with a stock boot. use the right caps you will not have any problems. They were designed by motorcycle people. ;D
I got a set of boots from JBM. They don't have vacuum barbs installed. I thought they did. I checked the web site and it says that they stopped putting barbs on fro strenght purposes. I guess I have to try to pull the barbs from my old ones and drill these. He told me I do not need a gasket. If I need a gasket I guess I wont be riding tomorrow. I am very disapointed.
10: I would not drill them, or put your barbs in them,, ( they may break, due to lack of strength purposes ??) there is another way to do that.....I think by putting a port, in the carb, take out a screw, put in little port ? I know your dealing 34's i may be mixed up,with my 38s... and you have those famous "vacuum" pets cocks, or did you get converted to old style ? ( and you may need barbs) If you need gaskets, call me,, PM, or e-mail me, (Sunday - day light hours) and i will go out in the garage, see if I have two extra, ( I think I do) Drove down 194 today, never have I seen so many cars, at your carnival !. Preston
I do think you need gaskets for the reasons that 5twins stated in his last post in this thread.
However -- and I will probably get flack for this -- I think snyching with a manometer is over-rated. You can get a very close sync with the paper slip method. Put a thin strip of paper under an almost-closed throttle plate. Adjust the plate until the paper pulls out with a slight drag. Do the other plate the same way. I have used this method (on a few different BS38s), and then tested it with a manometer, and the paper method was almost perfect every time.
It is my understanding that synching only has an appreciable effect at low rpm anyway.
Now, if you need the barbs to operate vacuum petcocks, that may be a different story. I would be very reluctant to drill holes in my brand new boots, especially if the guy who makes them thinks it is a bad idea and won't do it.
Last Edit: Jul 9, 2011 22:18:20 GMT -5 by dogbunny
Post by jefferytodd on Jul 9, 2011 22:52:33 GMT -5
I have the JBM carb boots too and am very satisfied and did not want to drill them. I have a set of stock 77 carbs and got the nipple fittings from 650 Central that allows me to screw them directly into the carbs for carb syncing. When not syncing I remove the fittings and just replace the stock screws to block it off thereby not having to worry about a cap that could get dislodged. jtc
You'll catch no flack from me on either point, DB; I use doubled gaskets with JBM boots because of clearance issues on my TM36/68 carbies, and when it comes to synch, there's more than one way to skin that cat. And right you are re. synch error having greatest effect at low throttle openings--the difference between throttles makes up a far greater proportion of area exposed to engine vacuum at idle than it does at WOT. But synch error, if large enough, can make a difference in the cruising range, causing increased vibration, overheating on the side that's overworked, and excessive fuel consumption.
The manometer can yield diagnostic information while you're setting synch. For example, if synch wanders significantly off-idle, that can be a symptom of an intake valve going bad, and you can then confirm by other means. And it's faster to hook up the manometer than it is to pull the carbs and gauge the throttle plates.
I don't know why Don thinks it's a bad idea to drill the boots for barbs; the metal core is very thick, and there's more than enough material for you to tap for a pair of 5 mm. barbs and Loctite them in. I discovered just how thick the material is when the barb pulled out of one of my JBM boots and I enlarged the hole halfway down to give a bit of space for JB Weld to set up in--that barb hasn't misbehaved since.
Sometimes you have to make judgment calls, Norm. If you're going to use the vac barbs with a manometer, it's best to keep dimensions the same. I preferred repairing one boot with what was on hand to modifying both. The repair is as strong as it needs to be.
I am going to try to get the old barbs out and then drill. We'll see. I am going to use Prestons gaskets because the carbs just barely make it to the stock air cleaners. I made a thin set of gaskets with some gasket material I had laying around. They sealed up ok but not thick enough. Had to pull it apart anyway since it started missing again last wed. on the way home from work. It is so intermittant that it is driving me crazy. I am really beginning to think it is electrical. BTW.. Thanks for the gaskets Preston. Will repay you soon.
r80rt: :)This is a splendid write up, THANK YOU!!!!
Dec 26, 2015 16:54:05 GMT -5
mashermoto: What the what is this shoutbox for? Or should I shout, WHAT THE WHAT IS THIS SHOUTBOX FOR!
May 12, 2016 22:22:21 GMT -5
motormike: Good Day ...just a FYI.. Wild Cat is this Labor Day weekend. Still go'n on. A few 650's still make the scene. Various rides at different skill levels each day.. awards dinner sunday eve. BS in the park'n lot after dinner.
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kardon: Wow quiet here, where did they all go.
Oct 7, 2016 2:18:13 GMT -5
gggGary: XS650.com LOL
Feb 16, 2017 20:49:02 GMT -5
buell88: Anybody have any idea who built the xs650 tracker used in the Draggin Jeans Ad on Pipeburn?
May 16, 2017 16:24:09 GMT -5
joshua: The regulator/rectifier unit I got from Mikes PMA has closer hole spacing than original. Are we supposed to mill the holes to fit?
Jun 7, 2017 19:25:58 GMT -5
joshua: My bad. I found the bracket they supplied to mount the rectifier/regulator... Uh oh. How is this meant to work? Which way is it meant to mount? Looks like I have to use some spacers or something. Good instructions would be nice.
Jun 7, 2017 22:09:52 GMT -5
craig8johnson: Not sure if this is the right spot or not but oh well...
Jul 11, 2017 18:04:15 GMT -5
craig8johnson: I'm checking the charging system. I'm afraid I might have fried the last battery. With the solid state regulator (after market) what should it be charging at. The book says, I think, 15 volts. I'm hitting 17 when revved. Is that too high?
Jul 11, 2017 18:06:19 GMT -5
gggGary: Yes 17 volts is too high, about 14 volts is max, sounds like you don't have the right regulator or it's wired wrong.
Jul 13, 2017 6:54:33 GMT -5
dean: Just saying Hello, new member who is going to fix up a 79 XS650 that has seen its better days. I will definitely have lots of questions coming up.
Jun 23, 2018 16:45:32 GMT -5
tt650: Trying to breathe life into a 1980 that's been stored (indoors) for 25 yrs. Air filters are dry rotted. Have cleaned carbs but she only runs briefly on choke then stops. Need jet setting info and other ideas that might help her idle and rev.
Jul 3, 2018 19:15:19 GMT -5
trix13: Hey everyone! New to the forum and am fighting those gremlins!! New charging system, ignition switch, coil and fuse box. Resistance is higher than normal on the ignition pick up so I'm trying to find one. No such luck yet.
Aug 16, 2018 8:50:48 GMT -5
trix13: Also, even though all of my connections are clean, I cannot seem to find out why , when at higher rpms, I hit the signals and the rpms pulse with the signals...hahah. same with the brake light. I appreciate all input!!
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Jun 6, 2019 10:52:10 GMT -5
adlpc: Hello all! Been enjoying your edifying posts and discussions - and as a fan of the XS650 since my early teenage years happy that I now own a 1980 Special which I plan to turn into a vintage half faired racer. Thank you all for being here!
Oct 1, 2019 0:58:56 GMT -5
jimothyj: Hello everyone, I just joined & wish would have known about this site in 2014 when I brought my 1974 TX650A back from the grave. I have spent a good deal of $$ and alot of time on it. Just painted it and working on electrical, I will post pics soon,
Apr 10, 2021 2:14:13 GMT -5
louisvan: trix13 - I had a problem with my 1975 SX650. When I got to highway speeds, the engine lost power. The problem was in the connectors. At a certain vibration and the wind pushing on the wiring loom, the connector lost continuity. A bad crimp to the wire.
May 20, 2021 1:19:09 GMT -5