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  1. 650performance

    Couple VM34 questions?

    Griz, would you plz email me at ctweeks@aol.com.
  2. 650performance

    Best Front Brake Pads

    Jabcb has the right idea. Contact Michael at Vintage Brake. He's THE expert on brakes for these bikes in both race and street trim.
  3. 650performance

    Why bad handling reputation?

    Most of the AHRMA Sportsman 750 road racers who run XS650-based bikes use the stock frame, but spend a lot of time optimizing things. Later 35mm forks with Race-Tech innards and a brace, new bearings in the steering stem, upgraded swingarm pivot components, braced swingarm, remove all the frame...
  4. 650performance

    stock bore size and a shell #1

    Michael Morse at 650 Central can sell you a pair of pre-jetted VM34s that will work well with your combination. Yes, it's a more expensive, but it's one solution that will solve your carb dilemma. He can also help you with follow up questions ... if, for example, you decide to make the engine...
  5. 650performance

    stock bore size and a shell #1

    ERG, Griz is right about the VM34s coming in lots of iterations. Racers in the '70s used to use VM34 carbs off Yamaha TD race engines for their XS750 flat track bikes and they were quite different internally. Check things out carefully before you buy. And, FYI, those TM34 carbs will handle up...
  6. 650performance

    stock bore size and a shell #1

    Great advice to ERG, Griz. I've never put together anything with a #1 cam that was less than a full 750 and 10+ - 1 c.r.. What ignition timing would you suggest to ERG as a starting point? I've always used 33 - 36 as a full advance setting for my engines
  7. 650performance

    XS650 Progressive Shocks? Hmmm

    Talk with Michael Morse at 650 Central. He's successfully set these bikes up to handle properly for both street and road racing and can tell you exactly what works and what doesn't. 650central.com is the url.
  8. 650performance

    XR Valves

    If I were looking at updating the valve train I'd purchase (used?) IN and EX XR valves from Darcy (darcyracing.com) or a flat tracker who runs XRs and copy the shapes on either a new set of valves from, e.g. Kibblewhite, who will make small batch or one off valves from their inventory of...
  9. 650performance

    XR Valves

    Jack, Harry Lillie used the valves from the initial 1972 alloy XR750 as models for his combustion chamber design. He later had copies made in slightly larger sizes. The ones I've used that came from the original stock of parts he sold me are typically 37mm (or slightly more) for the EX and...
  10. 650performance

    E3 Spark Plugs

    I can only speak from my personal experience. But, based upon that I believe, 1) Iridium plugs won't add any noticeable power to a stock or mostly stock engine, 2) they resist fouling better than any other plug I've ever used (I like to tune the race engines so they are fairly rich coming off...
  11. 650performance

    E3 Spark Plugs

    My friend Paul recently retired as a product specialist for Denso, a very large OEM and aftermarket spark plug manufacturer among other things. One of his responsibilities was non-OEM spark plugs. Denso's Iridium plugs are used by factory racing teams all over the world, including Toyota, MBZ...
  12. 650performance

    Any of you guys had your XS's down the 1/4 ?

    TwoMany, the low weight is the result of a C&J dirt track frame, Kosman rear hub, fiberglass body work, clip-ons, alloy rims, hollow axle, single disc up front, magnesium master cylinders, small disc on the rear and lots of 7075 aluminum for the triple trees, engine & foot peg brackets, etc.
  13. 650performance

    Any of you guys had your XS's down the 1/4 ?

    I ran my road racer at Sacramento Raceway (I think it was in the early '90s) and without any gearing optimization nor a full, clutch burning start the bike ran 11.85 and 111 - 112 mph. I was trying a new engine configuration and it later dyno'd at 68 RWHP. The bike weighed 315 with some fuel...
  14. 650performance

    Power

    Gary, you and I are more or less from the same generation. In other words, we've been around a long time and the one thing we've seen in decades of racing and hanging around high performance bikes and cars is that there is bench racing horsepower and performance and then there's the real thing...
  15. 650performance

    Power

    In at least one way the discussion is moot. Whether it is old or new technology used to optimize a XS650 stock head casting, you are still hemmed in by the fact that things will start breaking over 72 - 73 or so RWHP. And that power number is available with "old" gas flow technology. The...
  16. 650performance

    Anyone used or using a 250-30 megacycle cam for 750?

    Because the stock ports are, even for a 750 kitted engine, slightly too large to begin with, you can't really remove any metal unless you really know what you're doing. Even small mistakes can reduce performance by slowing gas velocity down and/or negatively affecting where turbulence occurs...
  17. 650performance

    Power

    Yes, I have used the exhaust port inserts sold by Michael Morse in my race engines fitted with Lillie heads for over ten years. They help produce a very smooth power curve, which is noticeable in some throttle roll on situations, and do not detract from maximum power, which in my engines vary...
  18. 650performance

    Anyone used or using a 250-30 megacycle cam for 750?

    I've used them in race engine with excellent results. It will easily support 70 RWHP in a well-prepared engine with proper port work. The Megacycle web site says that you must cut .080" off the guide length. It's isn't a big deal, any machine shop can do the work. The cam itself is a bit...
  19. 650performance

    retorqued head now Base gasket leaking

    30 lbs. of torque isn't necessary and can cause distortion, which creates its own problems. On 750cc race engines you only need 27 - 28 lbs. Bud Aksland, who build KR's engines used a 1" long & 1/8" thick steel shim that fit between the fins under the head bolts to spread the load out and...
  20. 650performance

    Valve Springs question

    Don't take a chance on mystery valve springs. This is not an area to try and save money. If you aren't sure they're real Yamaha parts then buy from R/D. They don't sell junk and actually know what they're doing, so you can ask questions and get real answers. Follow Griz's advice to set the...
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