1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Thinking about building a race bike out of an unlikely candidate

Discussion in 'WERA Vintage' started by Doc_Rot, Sep 3, 2020.

  1. Doc_Rot

    Doc_Rot Active Member

    New member here. I have to say this forum seems great! It was a tossup for WERA and AHRMA and after reading the rulebooks and poking around WERA seems like a better fit for me.

    I have inadvertently set on a course to own the most expensive KZ750 twin in the world. I recently found a guy racing one in Canada and after chatting on the phone with him he convinced me to build a race bike. So far I am about halfway through a in depth custom engine build. This has been a challenge because there is almost zero aftermarket support, so its been a bit of a money pit, but hey if I was into smart financial decisions I wouldn't own vintage bikes.

    engine specs so far are:

    Custom flat top JE pistons - 86mm - 906cc 10.25/1CR
    LA Sleeve iron liners
    Mega cycle cams
    full titanium valve train
    port and polish
    undercut trans
    balanced rotating assembly
    swapped for late model aluminum clutch basket

    The guy in Canada is telling me he got the weight down to 350lbs which I find astonishing. I think 400lbs would be a good goal. With this engine configuration I expect to be around 80-85HP. I think would be racing in V4 with this setup. Do these numbers seem like it could be competitive?

    I have done a couple track days and really enjoyed them but i have never done any racing. I'm located in Southern California and saw there was a race for WERA west in November. not sure what the protocol is for spectating is but I thought I would check it out.

    I'm mostly poking around here now trying to plan the new race build as the bike I previously built with this engine in mind is too pretty to race and i would rather start from scratch at this point. I'm sure I will have many questions. thanks in advance.

    -Victor

    PS. here is a pic of my KZ750 before the engine came out (again). With cams, carbs, pipe, and decked head I got 62 HP to the wheel out of the stock bore.

    kz750_11.jpg
     
    Last edited: Sep 3, 2020
    L8RSK8R, britx303 and wheelz96 like this.
  2. cyclocrossfool

    cyclocrossfool Well-Known Member

  3. FZRCraig

    FZRCraig Offensive to Most

    I have been on a few tracks with that KZ in Canada - not raced against it, but in practice and such. It gets around the track shockingly well (OK, the rider has something to do with that as well).
     
  4. JCW

    JCW Well-Known Member

  5. cyclocrossfool

    cyclocrossfool Well-Known Member

    thats not mine. although if i had one i would race it
     
    JCW likes this.
  6. britx303

    britx303 Boomstick Butcher…..

    DO IT!!!!! It’s always awesome when underdog bikes get raced regardless!!! :clap: P.s. great looking bike!!:bow:
     
    Chuck78 likes this.
  7. JCW

    JCW Well-Known Member

    If this is the docrot on the kz forums, his builds are beautiful. Some of the best I've seen.
    Almost too good to crash...
     
  8. t500racer

    t500racer Never Fails To Fail

    Raced against that bike several times at Shannonville years ago. Beat me every time.

    You could watch the frame twist he rode it so hard. I'll never forget watching him come by...
     
    Chuck78 likes this.
  9. Doc_Rot

    Doc_Rot Active Member

    Thanks for the welcome guys. That photo is of Fernando and his 750twin, that's the guy I talked to in Canada. He has been a huge source of information on these engines and the main inspiration for racing in the first place.
     
    VFR#52 likes this.
  10. fastfreddie

    fastfreddie Midnight Oil Garage

    That's a beautiful KZ. Please put those pristine OEM bits in proper storage and find some (refinished) beater gas tank to mount on the race bike.
    And don't leave us hangin'...we wanna see the the metamorphosis. Build threads are few and far between here, but your bike could be epic. :beer:
     
    SpeedyE likes this.
  11. Doc_Rot

    Doc_Rot Active Member

    That is a huge compliment because there are almost no OEM parts left on that bike! The goal on that bike was to build a version of the 750 twin like Kawi should have done it, not the super bulky parts bin special it was. the only things that are stock is 80% of the frame and engine cases. I have gotten really into fabrication in the last couple years and nearly everything on that bike is custom or aftermarket, I even cast my own ignition cover. check out a stock KZ750B and you will see how much was changed.

    This is my current plan:
    Finish building 906cc engine and drop it into the green bike to test it and ride it a bit, see if everything is good.
    Find a crusty KZ750 twin to build as race bike
    Build stock engine for the green bike and sell it.
    Build race bike with 906 cc engine.

    My immediate question is in regards to what carbs are legal for V4. If I'm reading the rulebook correctly I can use any carb (or technology) that was in existence before 1982. Do flat-slide carbs fall into that category? I have been thinking about finding a used set of FCR 39mm carbs and modifying the rack for this engine. Other options would be CR round-slide carbs but I don't think they come in 39mm.
     
    fastfreddie likes this.
  12. cyclocrossfool

    cyclocrossfool Well-Known Member

    lectron where around in 82 i think. i see a bunch of cr keihins on ebay for the triumph twins, wonder what size they are?
     
  13. kenessex

    kenessex unregistered user

    I ran Lectrons on my CB350 in 1982 and they were pretty commonly available.
     
  14. fastfreddie

    fastfreddie Midnight Oil Garage

    According to the rulebook, I don't know that FCRs will fly, at least not based on their introduction date . However, "Updating and backdating is permitted within the category dates. Components of later date may be used provided the design and operating principles of the component is essentially unaltered." While Lectrons had a flat slide, you might petition the powers that be that, yes, the technology for "flat" slide design carburetors existed prior to your cut-off date and so, FCRs should be allowed. Cross your fingers.

    An '82 is V5 with WERA.

    If it was your handy-work that made that KZ so beautiful, Doc_Rot, then it is also amazing. :bow: Had you not said anything, I woulda sworn that was the best looking KZ I had ever seen...minus that pipe. C'mon, man! Where's the blacked out Kerker? :D
     
    Last edited: Sep 3, 2020
  15. britx303

    britx303 Boomstick Butcher…..

    Yes, I realise you’re kidding........but that exhaust he’s got looks like the nicest set I’ve ever seen on an old cow 4 stroke:D
     
  16. Doc_Rot

    Doc_Rot Active Member

    IS V4 not the correct class for this bike?
    Vintage 4
    Pre 1982 Twins/Triples up to 1000cc.
    Pre 1979 SOHC up to 840cc.
    Pre 1982 Air cooled, 4-stroke OHC multi cylinders up to 570cc. Twin shock only, twin piston opposed Lockheed style calipers permitted.


    That exhaust was the first one I ever made. It came out OK. I tried sand bending the primaries with a torch a la Yoshimura and that was way more difficult than expected but was able to get the lower big radius bend done in that fashion. I will be making a new exhaust for the 906 engine. Burns Stainless offers free header calculations so I submitted my info and they suggested a step up 12" along the primary and next size up on the collector. Also I will be re making it because of the weight-saving to be had there. I used 16GA stainless for everything and its pretty heavy. I bought some 18 GA bends for the primary and will use an aluminum can to get the weight down. I think it will weigh about 5-6 lbs less.

    Back to the carbs - What carbs are most people running in these classes? Is there someone I can ask if a certain carb is allowed? I have no experience with Lectron carbs, i have seen them used on drag bikes, and have been told they are best at WOT applications, is anybody here roadracing them?

    kz750_14.jpg
     
    cyclocrossfool likes this.
  17. cyclocrossfool

    cyclocrossfool Well-Known Member

    V4,5 6lw is 750. do 4 and 5. dont worry about other people, put carbs on it that will work, round slide mikuni or keihin 4 stroke. get a bike ready to race. now. too much thinking. its vintage/ fun.
     
    Doc_Rot likes this.
  18. fastfreddie

    fastfreddie Midnight Oil Garage

    V5, Pre-1983, meaning up to Dec 31, 1982. Even lists KZ750 as eligible.
     
  19. Kurlon

    Kurlon Well-Known Member

    "Race bike out of an unlikely candidate" and I see no mention of Suzuki Savages, Yamaha Viragos, CFMoto... I've been mislead by the title!
     
    britx303 likes this.
  20. britx303

    britx303 Boomstick Butcher…..

    I had a savage................:crackup:
     

Share This Page