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1979 XS750

This is a discussion on 1979 XS750 within the Project Builds forums, part of the Caferacer.net Forums category; Here are some pics of my '79 Yamaha XS750. Bought it about a year ago as a project bike, cheap. Was a bit more of ...

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Thread: 1979 XS750

  1. #1
    Member franky996's Avatar
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    1979 XS750

    Here are some pics of my '79 Yamaha XS750. Bought it about a year ago as a project bike, cheap. Was a bit more of a project than I thought it would be, but oh well, I'm making progress.
    I wanted to build something like a street tracker/ flat track style bike, just something to run around town and have some fun.

    I cut the rear frame, made a fiberglass tail, smoothed out the tank. The wiring was all messed up and I needed a new rectifier and a used stator and stator cover. I didn't like the 2 petcock setup, so i welded one side shut and got a weld in bung and a new petcock for the other side.Since I had made that tail, I also made a seat pan and had a friend of mine make the seat for me, which i think totally fits the old look of the bike.








    Now I need to make a battery box and hide the wires, address some smaller things here and there. Was also thinking of getting a different handle bar, something like dirt bike bars. And of course new tires, flat track style.
    2000 Yamaha R1, full custom built, 365lbs wet
    2006 Suzuki Hayabusa

  2. #2
    Senior Member Swagger's Avatar
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    I am a HUGE fan of that platform, helluva engine too.

    The very best thing you can do for the chassis is throw those forks as far as you possibly can. They suck at anything other than tooling around town; too hevy and WAY TOO flexy. The hinge in the middle of the XS750.850 is mostly the forks and to a lesser extent the swingarm. You can get any number of good front ends that can be fitted to that bike, the one I used was a K75 41mm Showa front end I got at a swapmeet for $75 I think. It was so good on the 850 that I grabbed another one for another build.
    Due to the width of the engine, I wouldn't be too quick to drop the front end, but you can and should raise the ass an inch though closer to 1.5" felt pretty nice when tossing it into corners.
    A lower loop brace welded in will shore up the rear end pretty well, 1.25"od. x .065" is fine, use 1"d uprights and plate in the narrow joint at the back and you'll be dialed. There's also a lot of weight hanging off the axle so the more you spend on the shocks out back the happier you'll be.

    That engine also LOVES port work; clean up the short side and blend the bowls and valve guide protrusions and run the latest 850 cams you can get your hands on. The ignition is really quite good but likely your wires are OE and haggard, replace them and run some Dyna 5ohm coils, you cna go three ohm but they draw lots of current. It's got a 120* crank so your scavenging should be pretty good at upper RPMs with a long primary 3-1, but 3-3 sounds REALLY GOOD, kinda like a demented Ferarri.

    More than you wanted huh? haha....
    I have reams of info on this bike. Wanna build a 1035cc? Can do....
    Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices, but honestly and courageously uses his intelligence and fulfills the duty to express the results of his thought in clear form.
    ~Albert Einstein

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    Senior Member kenessex's Avatar
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    Besides the forks being an issue, the rear wheel and shaft drive are a problem, too. I would replace the entire front end with one off an FZR600 or YZF600. I would also convert it to chain drive and use a YZ/IT 465/490 swingarm with a YZF600 rear wheel.

    Ken
    WERA 119
    CCS 119
    CRA 119
    AHRMA not anymore
    \"Think twice before you speak, and then you may be able to say something more insulting than if you spoke right out at once.\"
    Evan Esar
    Newbies, Geeto and Tex (Bye Tex)hate me!!

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  5. #4
    Member franky996's Avatar
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    Good info on all the chassis upgrades. I had thought about doing a chain drive conversion, but haven't looked into it to much to see if anyone makes a kit or if I have to get the parts machined. Right now I want to finish it so I can ride it this season.
    2000 Yamaha R1, full custom built, 365lbs wet
    2006 Suzuki Hayabusa

  6. #5
    Senior Member Swagger's Avatar
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    Haha....Ken you make me smile every time pal!

    Ken really likes the IT465 swingarm, he's mentioned it to me at least twice and someone else once that I know of. Truth is though it's a pretty snazzy looking alloy swingarm. You'd need to source a shock but you can get an R1/6 piece of the toobz for less than $50, a new spring and a re-valve; probably $250-$350 From a good shop. The rsult would be pretty nifty after you add the top shock mount!

    Chaindrive can be done, there was a kat on the XS11 and Triple's groups that was selling a pretty nicely machined piece but it was $500 and pretty chunky. You can do it pretty well yourself with some long high strength bolts some alloy standoffs and a bearing plate. An XS650 sprocket will work though you'll need a clip groove ground into the output shaft which entails about -3 minutes on the lathe to add.

    Back to the shaft setup though....it's not really all that bad, BMW/Guzi have done just fine with shaft drive. It may not be the ultimate in ultimate high performance BUT.....you don't have to eff with it and in this case it's STOUT. If you need taller gears you can swap to the pumpkin from an XS11, in their great wisdom they gave the freight-train the quick gears....is a heavy bike though.

    A little extra rear wheelbase can be had with the swingarm from a later twin shock Virago, I want to say it's a red hair over 2" which is good as these bikes are rear biased in the chub department. You can pie cut the frame under the neck and stand the nose up to 25* before you run into clearance issue at full stuff. Go to a lower profile front time or even better something smaller in diameter and hopefully lighter? I've seen one that was running a static 24* with a 17" front wheel. Dunno how much fab you do but it looks from the work you have already done, the backgrounds in your pics and lack of rotten attitude (hang around a while longer, it'll come) I'd bet you have some experience in a shop and with bikes so even if it's not something you're comfortable with I'd bet you can find someone who can.

    If you're looking to keep/make it a tracker then you're well on your way though I'd definitely think about either putting your front fender on or fitting a brace....those forks are really pretty weak and will be more so without any kind of brace.
    Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices, but honestly and courageously uses his intelligence and fulfills the duty to express the results of his thought in clear form.
    ~Albert Einstein

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    Senior Member kenessex's Avatar
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    Swagger,
    The main issue I have with the shaft drive set-up is the rear wheel size. I just don't think a 130-18 tire is what you really need if you get the rest of the bike set up right. By the time you take all the effort and expense that is needed to get a decent size tire, like 160-17, in there with the shaft, you might as well have converted to chain. I think you are right that the only conversion kit I have seen was way over engineered and the same could be accomplished the way you suggested.

    Ken
    WERA 119
    CCS 119
    CRA 119
    AHRMA not anymore
    \"Think twice before you speak, and then you may be able to say something more insulting than if you spoke right out at once.\"
    Evan Esar
    Newbies, Geeto and Tex (Bye Tex)hate me!!

  8. #7
    Senior Member Swagger's Avatar
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    Yeah I'd like to see something closer to a 140 or 150 out back, wider isn't needed.
    There was a kat on the XS owner's group (one of them) that had his OE rim widened to 3.5" and reworked his swingarm to clear by cutting away the portion the tire(150 IIRC) interfered with and bracing out from there. It was fairly cleanly done and the shaft runs dry so no big deal with fluid management.

    But yeah...chain is the way to go if you want to do anything serious....


    Oh...haha and I bought an IT465 swingarm for my 920 after Ken reminded me of them. Almost a bolt on.
    Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices, but honestly and courageously uses his intelligence and fulfills the duty to express the results of his thought in clear form.
    ~Albert Einstein

  9. #8
    Member franky996's Avatar
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    Is there a rear wheel that fits from another bike? Something a bit wider? I don't mind cutting the swingarm where the tire meets , to get some more clearance. Cut a section out, and weld a brace in it. And does anyone know if there are other carbs than can be made to fit, like from a newer bike? Since it's a 3cylinder, it's probably hard to find something with the right spacing
    2000 Yamaha R1, full custom built, 365lbs wet
    2006 Suzuki Hayabusa

  10. #9
    Member franky996's Avatar
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    Took the old XS out for the first time last night. Local bike night. I like how it rides and sounds. Just have to work on the brakes a bit , they seem to get somewhat stuck sometimes. Gonna take them apart and see what's up inside the caliper.

    2000 Yamaha R1, full custom built, 365lbs wet
    2006 Suzuki Hayabusa

  11. #10
    Senior Member Swagger's Avatar
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    The carbs and header from any mid-90's generation Hinckley Triumph (750/900) can be fitted with very little worry. The carbs slot in mechanically just fine, no special bits needed, as far as I can remember it even took the OE throttle cable with just a little finessing. Short of going to a rack of VM32s this is a great cheap-ass hop-up for your engine. I've seen racks go for under $50 looking fresh and pink and new on fleabay so deals can be had.

    The header can be fitted by reworking the flanges to suit the XS engine and one could do well taking an inch out of the tubes that run down from the ports to snug it up a bit but it's not imperative.

    The point is the cylinder spacing is perfect and it's been done, there's a few kats on the yamaha triples group running the carbs and at least one with a Daytona header....

    As for a wider wheel, well I don't know of anything that's a drop-in. >xs1100 will have a wider wheel, I believe the options are 17x4.5 or 18x4 IIRC.
    >Seca 900 wheels will swap
    >Virago wheels will swap as will those from a V-star 1100 (a way to build spokes)
    >Certain Maxim wheels can be wedged in


    Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices, but honestly and courageously uses his intelligence and fulfills the duty to express the results of his thought in clear form.
    ~Albert Einstein

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