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Silver Surfer

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  1. That response was to YzWill250 who had a misundestanding about the powervalves. My response to you is basically the same. The reason why you can turn over the engine with your hand is because the piston opens the intake ports and allows crankcase gasses to move into the cylinder. This is dynamic compression. The primary static compression the manual lists is just the ratio of volumes at TDC and BDC. If you don't like, agree with, or understand these numbers, then please contact the manufacturer and get clarification.
  2. Up to this point, we have only discussed static compression ratios (SCR as abbreviated), but not dynamic compression ratios (DCR). The traditional 2 stroke engine only had only static controls over timing. That is port size, shape, and location in the cylinder, and the piston moving up and covering and opening them provided the only real timing of combustion events. Once the powervalve was invented, an additional dynamic control was introduced. This controls the timing of the return pulse from the pipe back to the cylinder (uses a centrifugal weight that changes with RPM's to open and close it). Its not a poppet valve like a 4 stroke that totally seals the cylinder...it just changes the size and shape of the exhaust port. It only attempts to optimize the DYNAMIC COMPRESSION ratio. Most people talk about static compression ratios, and this is the mathematical relationship between the volume at BDC and TDC. However, air is compressible and things change at high RPM. Change gears for a moment... In a 4 stroke a "big cam" has a long intake valve duration. Since the valve stays open longer, more air is crammed in at high speed only. At low speed the velocity is not there, the air is not compressed, and the air is pushed back out (this is called "reversion") of the cylinder into the intake. If you have ever heard a hot rod with a real choppy idle, this is why. The engine is not efficient at low RPMs. To compensate for this reversion, you RAISE the compression ratio. There is a lot more detail about this here. Since a 2 stroke has no cam some reversion occurs to the intake port (returned to the crank case but the reed valve keeps it from going back to the carb). But most goes into the exhaust pipe, but the return pulse forces that back into the cylinder. This drastically raises the pressure in the cylinder (piston is moving up, return pulse from exhaust, and the ignition timing is starting the combustion process which introduces more heat and pressure). If you have ever ridden a 2 stroke and gotten on the pipe, you know there is no better feeling. Its like being on a rocket when all these events start working together. Its amazing to me that a 2 stroke can even idle at all. I hope I have explained that well enough.
  3. you kids ever hear of a search engine? http://en.wikipedia.org/wiki/KTM
  4. You are correct, the yellow wires are the AC from the coil. I would prefer to have my red/black from the r/r connected directly to the battery. The best would be to have black wire from the r/r, battery, and ground all at one central location. If you run into some wiring logistics you could ground the r/r to the frame separately.
  5. The adapter they speak of is just a fitting that screws directly into your spark plug hole and it also has a hose that connects up to the gauge. Since the RFVC head is so deep for the plug, you have to have this. The XR400 has an auto decompression mechanism built into the cam. I don't think I have heard of these going bad. It only kicks in when the crank/cam reverse directions. The manual decompression level may be suspect. A lot of folk have found that the lever is out of adjustment, causing the valve to remain open. Make sure it is loose, and disconnect if in doubt. If you are certain you are getting spark, then there is not a short in the kill switch (happens often). I would also try turning up the idle screw a few turns (turn to the right = more fuel/air). Make sure choke and fuel are on. If you have a hill, try rolling down it and opening the throttle till it starts.
  6. ding ding ding! WINNAH WINNAH CHICKEN DINNAH! Take the manifold boot off between the carb and engine. Use a small dab of grease if you need to help make the seal. This sounds like exactly what is going on.
  7. The RFVC engines don't use shim stacks. The Yamaha's do. But the XR's have an adjustment screw.
  8. when in doubt GAS IT! of course this can only take place after properly warming up the bike.
  9. i know its not stock, but it is an option http://www.xrsonly.com/content/index.php?page=shop.product_details&flypage=shop.flypage&product_id=195&category_id=32&manufacturer_id=0&option=com_virtuemart&Itemid=77
  10. as i understand it (i have never owned a wave rotor)... the advantage of the wave rotor is that it does not warp like a standard rotor. so i would look at your existing rotor now. it is warped --> then buy a wave rotor. if you ride through a lot of water or mud, you might consider a wave rotor.
  11. My XR400 has been a constant source of joy over the last few years. I have ridden this thing to hell and back* and it has never quit or complained. I am truly in love. The bike is stock (including suspension), except for Gordon's mods and some Pro Tapers. At Chadwick I ride with all kinds of people on new, fancy thumpers and pingers, Japanese and European makes of all engine sizes and modifications. None of them can outrun the XR. This the best thing that I have ever spent money on (including car insurance), which goes to prove that Honda should not have quit making this wonderful machine. Last weekend at Chadwick I was riding with a guy on a KTM 450. I told him I thought that radiators were Achille's Heel. He chuckled and said he never had a problem with them (he rides at a meduim pace). Later we were going up a hill climb replete with stair steps, ledges, roots, gravel, rocks (of all sizes), and ruts. I get to the top and began the waiting process. A few minutes later I start to walk down to inspect the scene. I hear a four stroke revving out of control and see a HUGE puff of smoke. I don't see the KTM or the rider, just smoke. Thankfully, he didn't crash or break the radiator, just over heated causing fluid to burp and dribble on the exhaust. I didn't say anything, just enjoyed the irony. Eventually, he made it up top. It's not a fancy bike. It's old school and it works. It never complains. I don't know what I would do without it. I hope everyone with an XR realizes what they have. ~Dan *50-100 miles/week during Summer months at Chadwick, MO. 20-40 miles/week during Winter months (not because of cold, but just lack of sunshine!).
  12. 07 kx450 should run fine on 93. could be a bad plug or that you are running lean
  13. i have seen one or two gas stations that carry 101 at the pump. in addition to everyone else's comments which are 100% accurate, it is my understanding that an engine with higher compression develops better low end power (sacrifices top end power), and vice versa.
  14. all honda's use a banjo bolt with the same thread pitch. i am not sure on the diameter, but thus far it has been my experience they are the same as well. 10mm diameter bolt with a 1.25 pitch.
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