Dual sidedraft mikuni?

D

Dowdriver

XS650 New Member
Messages
2
Reaction score
0
Points
1
Location
Albany Georgia. USA
Ok new here so first hello to everyone. I have previously owned a 1980 XS Special 2, restored it and loved it. Needed a new roof on the house and the estimator loved it more. Soooooo..........
Anyway the household finance manager has shown some pity and is allowing a new project. I figure on building a hybrid chop/bobber only it's gotta be different, and it has to handle a good bit better than the typical stretched out hiway flyer. I don't mind chopping and fabricating as I'm a do it yourselfer. Roadraced in the early to mid seventies and owned about everything at one time or another. So here we go.

Haven't picked up a bike yet, just in the imaginary stage but once upon a time I saw an XS that had the frame modded and a dual sidedraft carbuerator onboard. It might have been a solex, I doubt a zenith or a dellorto possibly. Anyone played with this before? I also figure to move the battery and electrics under a fake gastank shell and mount a large oil tank under the seat area as a fuel tank with an electric fuel pump and regulator. Not sure why but hey.... I just feel this might be my last slow build and I want it to stand out. Also has anyone used a wiseguy extended swingarm? Back problems kinda take the fun out of a hardtail and like I said I want it to handle if I get a bit stupid once in awhile.

Thanks to all of you for any help on thei. I promise I won't buy a great looking bike and trash it. I figure on just starting with a good frame, some imagination, and a little more patience than most folks have.
 
Hey Dowdriver, welcome to the forum!

I'm not familiar with a single Mikuni carb that has dual sidedraft throats. I've seen Dellortos and Weber dual sidedrafts, though. Showing my age some, but I still recall reading an article in Cycle magazine back in the 60s about a custom Triumph 500 twin in a Rickman frame that had a single Weber DCOE -- a 40mm, I want to say. Still remember a quote from the article, too: "Throttle twisters beware!". It was referring to the prodigious amount of fuel that was sucked into the motor during said action.

I can't think of any advantage offhand going with such a setup. You can achieve excellent performance with a set of Mikuni roundslides, even better with a set of Mikuni flatslides or Dellorto "pumpers."

Sounds to me like you'll want to be keeping the rear suspension with your project. A wise move, IMHO. The XS650 is a great platform that allows you to do just about anything you can think of, given enough time and resources. Keep us informed with your building plans once you've located a bike to customize.
 
Thanks much cooltouch. Don't need a lot of WFO at my age. I was actually remembering how all together cool it looked and how menacing. Kinda forgot it could actually be menacing. I have a half finished Suzuki TS400 street tracker project that probably would accomplish the same thing. Mainly the old sissybar style rear frame loop they all had after the accident. Thanks again and I will look into the carb offerings you gave.
 
I'm planning on running a single Mikuni Flatside TM with an accelerator pump on an XS650 i'm getting ready to build. The intel behind this decision claims that with a single setup you get extremely fast starts and very quick throttle response and the only down side is a little bit lost at full throttle but that's where the accelerator pump should step in...
 
jay760 said:
Do you mean like the weber carb on the wasp outfit on this link?

http://www.xs650.org.au/idle_talk.htm
Click to expand...

Very similar setup to the Weber on the 500cc Triumph in that article I saw back in the 60s. Note that the guy reported having some problems with it. I really think that's way too much carb for an XS. I had dual Weber 40 DCOEs on a Jensen GT I used to own -- 2 liter twin-cam 16 valve motor, and even with that setup, 40s were borderline too much, according to a Weber manual I own. Barely enough venturi effect with the minimum-size throats that were available for them.

Cheftay, I think you'll get good performance out of your single flatside conversion. Are you gonna build the manifold? The single Mikuni conversion is a popular one for Nortons. My 850 Commando had a single VM32 on it when I bought it. I was surprised that only a 32mm carb was used, but that seems to be the one everybody prefers. Great off-the-line acceleration, and according to an old Norton mechanic I know, the only downside is top-end, where the bike hits the wall at about 95 mph. I've never taken my old Norton up that fast for fear of something breaking, so the single Mikuni is plenty for me, even if it's just a VM32.
 
Nice! yeah the guys who's helping me weld the frame has given me a lot of advice on that, he said a 40mm would be to much even for a single carb conversion so i decided to just go right in the middle of what the stock carbs were... 38's and 34's.

I probably will end up making my own manifold which what i'm envisioning now is just an hard metal or plastic pipe that comes off the carb and forks into two that end up right into the stock rubber mounts. I'm gonna cut the top of the spine out of my frame and move it back to allow for the carb to sit directly behind-and-centered of the motor.
 
In terms of unobstructed spigot area, the TM36/68 is about equal to the BS38, at the high end of OEM spec--a good choice. You'll love that carburetor. Watch the intake tract length; the bends slow down the mixture, and if the intakes are too long you'll get fuel condensing out before it reaches the engine.
 
- from bob scogin
xs_frame_sketch.jpg


frame_side.jpg


BobaScogin2.jpg


- using something like this
P6080002.jpg


- could also use a frame like this bsa
BSAFrame.jpg
 
Say inxs, where'd you dig up that drawing of Bob's? I've always thought that bike he built, which I believe he named the Junkyard Dawg, was one of the nicest minimalist bikes around. As I recall he sold it not long after he finshed building it. There's a close-up photo of his manifold floating around -- I think over at Bob Bertaut's site. Yeah, here it is. Scroll about halfway down:

http://www.650motorcycles.com/scogin.html
 
- its made for the XS650 motor, is available over here-not cheap-and not useable in a stock frame

- yes, i like the build too, nice clean lines...sketch i found in a blog writeup somewhere
 
Bob Scogins built his 2-1 manifold. He has a pretty nice machine and welding shop, though, which helps. Can't say I've ever seen a cast version like what inxs shows before. Although if you're really creative and a consumate do-it-yourselfer, you could cast your own, a la David Gingery. Check out Lindsay Books for books Gingery wrote on the subject of building your own foundry and casting your own metal parts:

http://www.lindsaybks.com/

Just click on Gingery's link whenever you see it, and you'll get there. LOTS of other cool stuff at Lindsay's. I order their catalog for its entertainment value alone, although I'll admit to having bought more than a few books from them over the years.
 

Similar threads

W
1978 xs650 ran perfect, now it won't even fire. Need diagnostic help
Replies
6
Views
1K
fredintoon
fredintoon
F
XS650 Bobber build
Replies
16
Views
23K
Focusinprogress
F
cooltouch
78 E Cafe Project
2
Replies
20
Views
7K
cooltouch
cooltouch
Back
Top