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numroe

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    Australia
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    1. Riding MX bikes. 2. Watching MX bikes race. 3. Working on dirt bikes. 4. Most sport. 5. Chocolate

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  1. No. Sorry. Typo in my last post. Was thinking SOFTER. Edited that post. Consistent now with my first post to you. I'm not sure. I don't track all of Yamaha stock valving setups. I don't over think the bleed stack. I see it as a fine tune for the bleed/clicker oil path. And not helpful for trails where softer springs and initial movement helps. It has nothing to do with the height of the piston and reb stack. There is a collar inside the comp stack which supports the piston so that the comp shim are free to lift away from the piston and compress a little spring under them. The comp shims are literally free to move up and down with just a little spring force. Tight is 0.2mm. Very open is 0.5mm. That's the usable range. Personal preference requires a stiffer stack with more float gap or visa versa. I prefer a medium stack with a medium float gap, BUT a valve that is soft on very high speed so no spikes. That's probably because you have other issues or inefficiencies going on. Fix those and the overall result might be way better. eg1. you are not getting enough travel out of your 0.52 springs then you might not feel a rebound issue. eg2. When you turn in the reb clicker lots more to get good reb damping, the reduced bleed through the mid valve makes the already stiff mid comp feel far worse, so you prefer the reb clicker in the mid position. I have played around with reb stacks and springs a fair bit on my 2 stroke and 450F and I have no doubt there is a damping stack to match any spring. You can also fine tune the low speed reb damping for the spring preload. I also have some forks where the reb feels fine stock and I leave it alone. Your stack for those springs looks wrong. IMO.
  2. I'm not sure about your bleed stack specs. My memory isn't good enough on the arrangement with the thick washers and working shims. Just look at your base valves and ensure the inner end of the bleed path is open. Or blow compressed air down the end of shaft and feel for it coming out at the inner end. They are near the middle post in the alum base cup. When the bleed stack (thins shims) are reversed then those ports are open, which gives you more easy oil bleed for very low speed stroke movement. A stiffer bleed stack would make the comp base clicker adjustment less sensitive. Check the base bleed is open. Your base main stack is SOFTER [edit] than the MX stock setup, and the stock KYB SSS MX forks are plusher on rough trails than many poorly designed and valved Euro bike forks, so I wouldn't worry too much yet about your base being too stiff. Especially when you have a very beefy mid comp valve. Something like the stock 250X mid will be way more plush than what you have now. You must check your float gap too. If too tight then you will feel way too much front tyre feedback (chatter) on initial fast wheel travel. Also remember that too little damping will feel harsh too. For trails I think it's good to soften the very high speed damping which is why the 15.3 in the mid comp is so good. Also, in all my KYB and Showa forks I use a mid setup where the working shims are moderate in stiffness but I ensure the stack can blow open a long way when it needs to. It's long time since I worked on mine but something like 0.5mm more blow open can be very significant. That means carefully selecting your diam tapering in the working shims so more of them can deflect down inside the cup instead of landing on the cup rim as the face shims will do. The result is awesome since the mid speed damping force makes the fork hold up nicely, but on very fast hits there is no spike. It does mean the mid shims will deform faster, but i still get over 80 hrs out of mine before they look shagged out. And for any riding your reb needs to be reasonably suitable for your springs.
  3. Reb: Yours is way too fast (soft) for your springs. It should feel very harsh. Stock 250X will be much better. Better still will be if you add another 20 between the 13 and 18. And change to the stock 11mm clamp shim. Mid: Stock 250X will be much better. Your mid will have more of a spike on very fast speed hits with the two 17.3 cup shims. Using one 15.3 makes a massive difference. You will have to measure and choose your float gap. I strongly suspect you'll like it even more if you remove one of the 20mm face shims too. Base: You can see that yours is softer than the 250 MX stock setup (same 15mm clamp shim). The 250X has a much smaller clamp, so it takes a bit time to calc the effective stiffness and I don't have time. It's hard to guess what base setup you want for you weight, but for tight single track what you have is probably close and I'd leave the base stacks unchanged for now. Which saves you much time. See where you end up liking the base (comp) clicker. And remember that the right clicker setting is most plush and controlled. Clicker out doesn't always give a softer ride.
  4. No surprise you found those SSS forks to be a bit harsh. I think 0.42 springs are a little too soft for your weight and speed. Try them. But consider 0.44 later on. I'm using 0.42 on a YZ300 for trails and I'm 160 lbs and they work really good. Your base is much too stiff. If you stay with 17 face shims, then you'll need to taper down to a 14mm clamp shim. I'd always recommend a smaller clamp since the stack (and valve) can then blow open further for very high speed hits. Assuming large enough piston comp ports. Your mid might be okay, but you must measure the float gap (free lift) between the piston and first face shim. Should be around 0.35mm for rough trails. You also need to check the design and ensure the valve can blow open a long way for very high speed hits. Then you can smash into large things at speed and feel very little, but still get good damping hold up in the front for other more mild comp strokes. For rough trails, your reb is too slow on low speed. So swap that 14mm x-over shim for an 11 and ensure it's 0.12 or 0.15mm thick. If you go for stiffer 0.44 springs, then I'd recommend you slow down the reb mid speed by adding another 20 in the second stage stack. Do all that and I reckon you'll bloody love it, mate.
  5. I suspect that more than 25% of the reports on tires bring better or worse than another are because the bike's current suspension or chassis setup matches a tire more or less. Just a hunch based on my own experience. Seems most of them work better with a little tweaking.
  6. numroe

    Kx250f burning oil?

    So you let your motor run for 3 minutes without oil feed to the pump? Seems like asking for trouble. Maybe the backfiring happens because your exhaust pipe header is leaking air.
  7. numroe

    KX250f cams and valve buckets destroyed!

    In your original problem (back in Oct) I'm curious how the buckets got dented like yours did. The buckets push on the shims which push on the tip of each valve stem. So if the middle of each bucket is bent down then what was holding the buckets up? I guess either lack of lubrication and the bucket sides were seizing into the head, or else you forgot to install the (correct) valve spring retainers. Are you sure the head alum isn't worn in the bucket holes? In today's problem I'd recheck valve chain timing. Also use a new spark plug. And for peace of mind, confirm the oil pump is working by inspecting the cams to be smothered in fresh oil with the cam cover removed and spark plug out while you crank it over.
  8. numroe

    2013 KX 250f Will not start after rebuild

    You never mentioned if you triple checked the valve timing. Did you? If you did, then do you have a carb sitting around somewhere that you can connect to the intake to see if the motor will start?
  9. Did you try adjusting the rear spring preload or the clickers? Just curious. I enjoy testing new tires and feeling the differences. I believe that many tires of the exact same size have different rebound characteristics and air pressure changes often cannot compensate for it. eg. We can swap a tire and conclude it's worse, and it sure was, but perhaps all it needed was a small adjustment to the spring preload or the clickers.
  10. numroe

    2012 kx250f engine noise

    Do you mean the 2010 ?
  11. numroe

    4cs

    Did they do low cost re-valving mods? I think they can be made substantially better for the price of a basic re-valve. About 18 months ago I did some research on low cost mods for a friend's TC125 and concluded that the 4CS is a design with some good and bad ideas. The best info was from Terry Hay (here) and on the Valving Logic website. Thanks to both info sources. In summary I think it's a clever design to create some positive pressure on the damping fluid but the implementation is on the cheap side (to increase profits) and the damping settings are far from being versatile enough for common use (MX or trails). Overall I don't see how anyone could claim the 4CS is a success. The damper rod is steel to save costs, and had to be smaller diameter to keep the weight down. The small diam means it does not displace enough oil to make the base valve flow enough oil and the mid needs to flow too much oil. The stock base valving is too soft and too restrictive in the high flow mid valves. Just crazy. Extra crazy is the marketing people persuading the engineers to agree to having reb and comp clickers on the top of the fork, which means it has those one-way check valves giving less combined mid-valve bleed and extra harshness. Having no base clickers is just being cheap and nasty toward the customers. Luckily, good improvements are possible with some simple changes. The mid needs more bleed. So remove the one-way valves (so both top clickers become rebound) and tune your float gap for the amount of feedback you want. The mid flows more oil than an equiv size Japanese fork, so soften the mid comp stack. 30% softer worked for a 2015 MX setting. The base doesn't flow much oil, so it needs much more low speed damping (about 3 times stock!) and more high speed damping (up to double). So you end up with the base doing more work and the mid doing less. But the mids now share the workload. I also installed a more progressive reb stack (Jap style) with a x-over shim, and the front end follows the ground nicely. I didn't remove any internal seals to convert the fork to OC. I think Terry said that going OC helps reliability some how.
  12. If the 90kg guy rode MX, then it means you need to set it up for the bush. Doesn't matter what was done, the valving and/or spring rate will be wrong. If he did off road stuff then maybe the valving is usable for you and you need a softer spring. It's easy to self check your spring. As the other guys already said, set your rider sag to 105mm then measure your static sag (bike weight only) If the static sag is > 40mm then your spring is too stiff. If < 25mm it's too softer. Within that range and you are fine tuning. The massive sag you are using could make the rear feel harsh too. So far down in the stroke and the suspension will firm up too soon on most bumps. I like LIL's advice to stay in the 100 to 110 range. If you want to lower the bike a little and keep the shock working properly then hunt around for a lowering link (pull rod). Just a couple of mm longer might be what you like. Then lower the front by sliding the forks up. The bike's balance for stability and turning can be very sensitive and make a big difference to the fun factor so play around with front to rear heights a bit.
  13. numroe

    Cadj Stack Help

    I'm suspecting the issue is spring related. Are you certain the shock has correct gas pressure? Did you try firmer spring preload?
  14. numroe

    Cadj Stack Help

    Was that excessive squat with the HSC adjuster fully in the firm position? How responsive or effective is the HSC adjuster with the valving as it is? What is your LSC adjuster position now? What are your numbers for rider and static sag?
  15. numroe

    Valve shim question

    Try a new spark plug. They die.
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