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This is a discussion on xs750/850 within the Project Builds forums, part of the Caferacer.net Forums category; Originally Posted by Witworth You have spent a lot on parts, but you really have plenty of tuning work to do to get this thing ...

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Thread: xs750/850

  1. #11
    jcw
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    Quote Originally Posted by Witworth View Post
    You have spent a lot on parts, but you really have plenty of tuning work to do to get this thing running well. Like paying for a pro dyno tuner for a full day, at the least.

    If you have hotter cams, I really doubt 1.0mm+ IN valves would make much difference.

    If you think a shorty cool looking exhaust is going to be compatible with all your engine mods, think again.

    BTW, have you ever ridden one of these triples before plowing so much cash into it? Had to ask.

    With the rear jacked up, forget using clipons. You need some superbike bars to be able to throw the big heavy lump around.

    Danger, is my business."
    You are right on about the shaft. I have on multiple times asked myself WTF am I doing.
    My last modern bike was a shaft drive. But it was in a paralever rear end of a BMW k1200r. So, I was spoiled with a very nice riding shaftie.

    The clip ons aren't bad. The rear is not jacked up that high. In fact, #1 the seat actually might sit lower than stock.(take a look at the stock photos. the seat is a sofa cushion) #2 I purposely avoided a much longer than stock rear shock to avoid the excessive angle of the shaft drive and problems associated with that. Moving the pegs back with rearsets and new mounts are a must though. There's a couple goofy pics of a guy on an xs750 with stock pegs and clipons. let me see if i can find them...

    Hotter cams are relative. My lift is .380 I think. Maybe a little more. Not hot cams. Just warmed over. duration isn't over thee top. Don't see much need to rev it out. Listen, I'm not one of those delusional characters thinking i'm making a bike that'll outrun a modern sportbike. Realistically, I'm thinking 70hp at the wheel??? maybe. (even then that'll be almost double stock at the rear wheel). I've kinda built the engine with that idea. I keep in mind that it's still an aircooled triple!!! I didn't even go for the big bore kits which were actually cheaper than hunting down 0.5mm overbore NOS pistons and rings. (my god the rings were a pain to find)

    As far as the exhaust, I've ran the calculations and am looking at something like 31" long primaries 1 3/8" diameter and then a 3 into 1 flat collector than whatever reverse cone length I can fit. I'm more into function than looks. (BTW, It'll be my first exhaust system I tig together)

    Thanks, though, for your thoughts. I appreciate them. Keeps me grounded and thinking.
    Last edited by jcw; 07-18-2015 at 08:13 PM.

  2. #12
    jcw
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    Speaking of XS11 and shafts. I'll still be making less hp than a stock xs11. How bad was the shaft jacking in that bike?

    Oh yeah, I also managed to fit up the beefier XS11 final drive onto the xs850 swingarm and shaft. It gives me an even lower FD ratio. It took a little shaft and U-joint machining to fit but it worked.

  3. #13
    Banned Witworth's Avatar
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    Both the XS11 and the XS750 wind up and jack like crazy both on and aggressively off throttle.

    Good you have stock length shocks to go.

    Your exhaust design sounds feasible.

    Danger, is my business."

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  5. #14
    jcw
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    Here we go...

    clipons + stock pegs + low seat = pretzel

    Name:  1978-Yamaha-XS750-Dapper-Rat-Cafe-Racer-Project-3.jpg
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  6. #15
    jcw
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    Quote Originally Posted by Witworth View Post
    Both the XS11 and the XS750 wind up and jack like crazy both on and aggressively off throttle.

    Well that sucks...

    Guess it'll just be another poser at the local Starbicks.
    At least I won't be alone...

    As far as tuning, while I said this was my first bike build, I've tuned multiple EFI bikes. I have a serviceable datalogger with wide band o2 that I've used before. In the past I've fuel injected my zx-11. and tuned my K1200r. I'm not saying it's gonna be easy. That was the main reason I went with the FCR's. Not so much for the incredible power I'll be making (LOL) but the ease of tuning over the old Hitachi and Mikuni CV carbs.

    That said, I'm a complete carburetor illiterate. EFI, I can talk about. Carbs, not so much.
    Last edited by jcw; 07-18-2015 at 08:56 PM.

  7. #16
    Senior Member Ravivos's Avatar
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    Personally, i am a big fan of EFI, and currently converting a GS1200 bandit engine to EFI that will go into my 84 GSX750ES (Microsquirt).
    i say - EFI the hell out of it, should be fun.

  8. #17
    Banned Witworth's Avatar
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    Flatslides aren't the hardest things to tune. They are race carbs after all. Data logging is a bit of a joke for aircooled carbed bikes. Far too many variables on the road: speed, load, air temp and moisture in the air, for example. Air cooled bikes cylinder heads temps vary over a very wide range compared to watercooled ones. The data can just be plain useless. Dynos never lie.

    I would not waste my time fitting EFI to an old aircooled motorcycle. I'd just fit flatslides, and go. Bikes are not cars, as far as tuning goes.

    For the pipes I'd fit the longest primaries I could fit in the space allowed. Also I would not go more than 10% bigger in I.D. in the header pipes than stock. Fat header I.D.'s can just cause flat spots and torque holes in the mid range. An XS triple with no mid range torque is pretty useless. After all, mid range torque is one thing the 850 does well.

    Danger, is my business."
    Last edited by Witworth; 07-19-2015 at 03:05 AM.

  9. #18
    jcw
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    Quote Originally Posted by Ravivos View Post
    Personally, i am a big fan of EFI, and currently converting a GS1200 bandit engine to EFI that will go into my 84 GSX750ES (Microsquirt).
    i say - EFI the hell out of it, should be fun.
    If this bike was a better platform, I would consider it. But it's taken me way too long already. I want to get it up and running.
    Nothing like a nicely tuned EFI bike, though.

    Funny thing is a nicely tuned carb'd bike isn't too shabby either. My zx-11d in 1997 with carbs ran pretty much as well as my 2006 K1200r.

  10. #19
    jcw
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    Quote Originally Posted by Witworth View Post
    Flatslides aren't the hardest things to tune. They are race carbs after all. Data logging is a bit of a joke for aircooled carbed bikes. Far too many variables on the road: speed, load, air temp and moisture in the air, for example. Air cooled bikes cylinder heads temps vary over a very wide range compared to watercooled ones. The data can just be plain useless. Dynos never lie.

    I would not waste my time fitting EFI to an old aircooled motorcycle. I'd just fit flatslides, and go. Bikes are not cars, as far as tuning goes.

    For the pipes I'd fit the longest primaries I could fit in the space allowed. Also I would not go more than 10% bigger in I.D. in the header pipes than stock. Fat header I.D.'s can just cause flat spots and torque holes in the mid range. An XS triple with no mid range torque is pretty useless. After all, mid range torque is one thing the 850 does well.

    Danger, is my business."
    I look forward to getting the engine together and starting it up for the first time with those carbs.

    If a dyno is not a datalogger, what is it then? Getting the A/F ratios in-the-ball-park would be my primary goal with the datalogging. Whether that's done on a stretch of flat road or on a dyno makes little difference to me. There are differences, but little.

    There's a lot of calculators out there for calculating primary diameters. I've tried about 4-5 of them and get a "wide" range of diameters. Ultimately, I'm looking for primaries that are small enough to maintain exhaust gas velocity without choking the gases coming out of the head. I think I'll touch up the stock headers then weld up one the "next size" larger. I've got a stock system from a 1976. It's pretty heavy being double walled and at the connection points, the pipe is choked down to less than 1" with reinforcement. But it's got a gorgeous shape. About 1.12" ID which coincidentally is close to what I've been getting with my calculations. Start with that and move up from there.

  11. #20
    jcw
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    Here are the rearsets. Not the color I wanted but I found them on close out and really liked how they mounted and the adjustability.

    This is the mounting plate.


    Then the rearset.



    As you can see, the xs750 uses a stamped steel section for the swingarm pivots. Not the strongest of structures.
    I'm weighing the risks and benefits of drilling in that and welding a couple 3/4" steel bungs tapped for the mounting tabs bolts for the plate in the first pic.
    thoughts?
    Last edited by jcw; 07-20-2015 at 10:23 AM.

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