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Post by hopwheels on Feb 5, 2006 15:31:55 GMT -5
More proof of my super-novice status! So, I've got the throttle installed on the carb, and noticed some things about the VM38 that have created questions. The stock petcock has two lines, one for fuel, and the other I think is a vent line, smaller diameter, that on my other bike, connects to the engine side throat of the carb (for priming?). On the 38, the inlet on the carb for the main fuel line seems evident (larger diam. brass tube), but I can't seem to find where the other smaller line connects. As well, the 38 doesn't seem to have an overflow outlet requiring a line, unlike my other bike which I think has a 34mm Mik. I'm sure there are obvious answers for the experienced, but as for me... any help would be appreciated!!! Thanks guys!
Gary
Hopwheels
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Post by StewRoss on Feb 5, 2006 16:33:32 GMT -5
Gary,
Hi. The extra line at the back of the fuel tap is the vacuum line to operate the tap on and off automatically.
I have never used the original tap when changing carbs as I am usually also changing the tank for something other than and SR tank. If you cap the vac line off temporarily, you can use the tap in the Prime position, this will give an unrestricted flow. But you will have to turn it to another position, ON/RES once you have stopped the engine to absolutely preclude the possibility of fuel continuing to flow into the carb after shutdown.
There should be another tap that will suit the tank mounts on the SR. I have never bothered to check it out. Might be a useful thing to look into. I usually mount a high flow tap from something like a YZ or YZF on my alloy tanked babies.
The other thing you could do (provided there is room) is to sort out a spigot fitting that would mount through the rubber carb manifold. That would require some drilling of the rubber manifold and machining of a suitable piece of brass. You would then connect the spigot to the vac on the tap. That would then re-instate your vacuum for the normal operation of the tap.
There are also adaptor plates I've seen that mount between the carby manifold and the head that have a brass tube poking out of them for that very reason. Elongates your inlet tract a little...not at all a problem on the SR. One of mine is elongated (spaced back from the head) about 4 or 5 inches. Of course if you're running the standard airbox it may cause a few mounting issues.
Are you keeping your airbox as well?
Welcome to the world of modification...nothing is without some problem or other...like changing the carby cables etc.
There should be two vent lines on the VM38; one each side, more toward the front of the body.
I'll see if I have any pics of an adaptor plate...
SR
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Post by hopwheels on Feb 5, 2006 17:47:54 GMT -5
Thanks Stew. Good news about the vent lines. Bad news about the tap itself. I rebuilt the stock one on the '79 (time and expense) without figuring all this out. Guess I can fit it to my '78 when I restore it. It would be great to find a way to use it though. The adapter plate sounds promising. I'm going to check Sudco, here in the states, where I bought the carb. What about an XT500 tap? See auction below. I'm pretty sure it fits the SR tank—unmodified. cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=4608909841&fromMakeTrack=true |
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Post by StewRoss on Feb 6, 2006 5:06:56 GMT -5
Gary, It may fit, but I'd check the hole spacing on both first. I recall the SR may have been a little wider...easy to measure. Looks a little closer to me by eye...  I couldn't find the pics that I indicated I may have...I have so many pics that it becomes a real problem...one day I'll sort them out a little better. I seem to recall that it was from a Japanese website. One other option would be to drill and tap a small hole into the engine side of the carby body outlet. You'd need to do this carefully to prevent damage to the carby and you'd also need to fabricate a screwed-in brass spigot to mount the vac line to. You'd need to seal the scewed-in spigot from leakage. You really don't want any of it protruding into the carb throat area either...Should work OK. I haven't got a carby in front of me at the moment to see how much there is poking out between the slide housing and where the rubber isolator comes back to...but worth considering. A manual tap is by far the easiest option if you can get one to fit. I recall there may have been something on this topic on the Thumper Page...look there as well. May give you a name for a straight replacement tap? SR |
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Post by mikedeb on Feb 6, 2006 16:44:44 GMT -5
Gary, Mike's XS650 site has manual petcocks that will replace the OEM vacuum petcock. I did this conversion on a 78 XS750 because the stockers were leaking bad (even after a rebuild). The replacements look OEM and are high quality. Get the one for the late 70's 650. Mike www.mikesxs.com/ |
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Post by hopwheels on Feb 6, 2006 19:43:25 GMT -5
A new tap from mikesxs is on its way. Thanks Mike! And thanks for the info Stew! Much apppreciated as always. Now, on to the brakes...
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Post by StewRoss on Feb 6, 2006 20:44:04 GMT -5
No worries. Interesting site.
Perhaps the XS manifolds (with the vacuum tube) would fit the SR carby...always many ways of looking at things....
Keep up the good work on the SR...
SR
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Post by hopwheels on Feb 6, 2006 22:26:46 GMT -5
Hey Stew. I saw that carb holder/flange on the XS site and thought exactly the same thing! I almost bought both the tap and those flanges— to have both potential solutions at hand. Guess I can always use the rebuilt stock tap on my '78, whenever it may need it. Thanks again guys. Its pretty cool to get all jammed up on something and have you guys to turn to. THANKS!!!
Gary
Hopwheels
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Post by StewRoss on Feb 7, 2006 5:51:30 GMT -5
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Post by mikedeb on Feb 7, 2006 8:12:07 GMT -5
A new tap from mikesxs is on its way. Thanks Mike! And thanks for the info Stew! Much apppreciated as always. Now, on to the brakes... You're welcome Gary! Once it's installed it will look completely OEM. I don't know where you're at with the brakes but Mike's XS650 may have some of the items you're looking for. I believe the pistons for the later calipers will also fit ours. I noticed that the Yamaha part numbers are the same for the piston in a number of different calipers from that era. Also, Mike's sells some OEM style master cylinders for both single and dual disc applications. They are the ones with the full metal resevior instead of the nylon ones like ours. Mike's is going to be getting a bunch of my money over the next several months for some of the same items. ;D BTW, my Victoria seat arrived today. It is so cool! ;D |
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Post by hopwheels on Feb 7, 2006 10:09:24 GMT -5
Thanks for posting on thumperpages on this topic Stew. Very interesting. I was on the Pingel route yesterday as well, but their taps are arounbd $100 with the adapter. Wanted to save a little where I can (I'm not even going to add up this build cost so far, don't even want to know  ) I did buy all of my parts already on the brakes from Mikes XS, including the larger master cylinder. Thanks Mike. Rebuilt both front calipers. All parts, perfect fit. What I need to trouble shoot is a slight rubbing coming from the left rotor (I'm afraid to ask, because it only rubs on part of the rotation, about a third turn, hopefully not warped!!!!) Mike, did your Victoria seat come with rear brackets? I had to fab my own after failed attempts again to hear back from VD. Love the seat though. Gary Hopwheels |
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Post by mikedeb on Feb 7, 2006 17:45:08 GMT -5
Gary, Sounds like you're well on your way to having a nice brake setup. However, if you have a slight rub on the left rotor, that may be an indication that it is warped.  If you have access to a truing stand you can always check it. I just went through that with my Ducati Monster. Now I need a new rotor. Yes, the Victoria arrived with the brackets. I'm sorry to hear that yours didn't and you didn't have any success in communicating with VD. Keep us updated on how you're doing. Can't wait to read a ride report and see a final build pic. ;D Mike |
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Post by StewRoss on Feb 8, 2006 16:42:30 GMT -5
Gary,
Hi, no probems.
I have had one or two SR discs warp myself. I tried to straighten one on my lathe but had no real luck. I believe that it can be done by an 'expert'...but...
New SR's come with a semi floating front disc. Two may be better of course??? Unsprung weight...
Problem I have had with two front discs is with tank-slapping, probably due to their increased weight sitting out there.
I am going to fit a steering damper to my new cafe racer as it comes along. It has Yam R6 front forks (not R6 triple clamps though) and I'm fitting twin 298mm discs up front using the R6 calipers.
Even if you ran the steering damper at the lowest setting it should assist to sort out any possible slapping problems.
Of course tank-slapping has long been a contentious subject on the Thumper Page, with people saying that SR's don't tank-slap, and you must be doing something wrong to it, it can never happen on an SR....etc...
Believe me it can happen and often does in the right (wrong?) situation...I have now owned 4 SR's and still have 3. All of them at one time or another have tank slapped. One horrendously over some rough tarmac at about 120k's...I think that one was so bad due to the previous owner fitting incorrect (much heavier) fork springs for the meagre damping abilities of the standard SR forks. I have also gone back to one disc on the front of that bike and it is nowhere near as bad now.
Perhaps I do push mine a little too hard sometimes...but it doesn't always occur only at those times. Just be aware it can occur. Situations such as rippled tarmac corners etc. can set it off. In my mind the lighter the front wheel the better.
Now how did we get onto this topic talking about carburettors??
Perhaps this topic needs its own thread...unfortunately it can and often does attract some extremely differing opinions for some reason...some from way out there.....
SR
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Post by miker on Feb 8, 2006 20:30:37 GMT -5
Disc rubbing - I put a spoke front wheel (and the disc it came with) on my XS, it did the partial-revolution rubbing you describe. I unbolted the disc, carefully cleaned the area underneath, and reinstalled it, and it worked no prob.
miker
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jimc
New Member
Posts: 22
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Post by jimc on Mar 23, 2006 0:26:49 GMT -5
Hi everybody,
I've had my share of tankslappers on a single disk SR, even with a steering damper (though it was a modified frame with a steeper steering angle). My damper wasn't the best quality, in fact it may have had more of a psychological effect than any actual damping! But who cares, I like stoppies! I have a couple of floating disks off of an older Katana 600 (290mm). They seem to have the correct offset from the hub and the center hole is a perfect fit onto my hub (XS 650) but the only problem is the rotors have 5 holes, not a match for the 6 bolt pattern on the Yamaha. Has anyone tried to fill the old holes and re tap for a 5 bolt pattern?
Also, back to the carb manifold issue, has anyone tried these billet manifolds I've seen on e-bay recently? As I recall, Joe Minton used to like moving the carb back from the cylinder a few mm with a longer manifold. Better carburation at the lower end was the claim.
Hey Gary, I'm almost ready to look for you up in the hills around here. Get that thing sorted.
Jim
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If you have access to a truing stand you can always check it. I just went through that with my Ducati Monster. Now I need a new rotor.