VBS-Thumpstar

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About VBS-Thumpstar

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    Ontario
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    It would be shorter to list the things I don't do!
  1. We race Enduros and Hare Scrambles, fun stuff. Anyway... One of my sons will be turning 13 next March and moving up to an 85 class mini. His races are one hour long and he does pretty good on his KTM 65SX. However, he has a penchant for 4 stroke motors now but I am not buying a CRF150R. I have a 4 year old China clone bike with a 125 Lifan engine and he runs that around the yard rather than his 65. The bike has been beaten by a 225lbs adult since day one and the chassis is now a total pile. The motor still runs like a top despite being ridden like it was stolen every time out though. I was wondering if a pitbike like a Pitster Pro (just as an example) could be set up for a 100lbs rider to run one hour off-road races? The reality is that it wouldn't even need to be all that powerful, a regular 110-125 would have plenty of power in the woods, especially when it's wet and slick. We often run Rekluse autoclutches on our big bikes and some clone engines come with them already so that's a bonus. What about running bigger wheels? Bigger wheels go over obstacles better and I was wondering if a pitbike could be set up to run a 17" front and 14" rear wheel? (some already have the 14 rear I think) Any insight would be appreciated. Sean
  2. Any chance you would sell the SX and put that towards the purchase of an EXC? You tried one (an EXC) yourself so I don't have to tell you how night and day that 400 was from your 525. The drawbacks of the SX motor are the light crank and the close ratio 4 speed. While great on the track, they are unfortunately very hard to correct for trail riding. I'm lucky to have both a 525EXC and a 520SX. I tried my EXC at the MX track and while it's good for a while, it starts to take a beating when you get faster. So I bought the SX. Well as an experiment, I trail rode my SX with track gearing (14/48) and while OK in the fast stuff, it was not user-friendly in the slow stuff. First gear on the SX is almost equivalent to 2nd on the EXC and coupled with the light crank and racy ignition it can be quite a handful at times. Things you can do to tame it down are gearing changes, flywheel weight and different exhaust. 13/52 on the SX gets you pretty close to 14/50 on an EXC but that limits your top speed to about 70MPH in 4th gear@9000 RPM. (rev limit is 9800 RPM) If you can find a complete EXC transmission it can be installed into the SX engine cases. Extra flywheel weight will help to smooth out the power pulses. My SX still has the original exhaust but it has a Pro Moto Billet spark arrestor on it. This made the bike quieter and didn't kill the power too much. It is still as fast as the 450s but isn't as loud. Or you can also fit a complete EXC exhaust to your bike to soften the hit as well as make it quieter. Sean
  3. X2 Mine's been working great sofar. Love these things. Sean
  4. I thought it was a Honda one? If it's not a KTM wrench, it might not be the right length. The one D1k got me was too long to fit onto the spark plug with the tank in place. The end is a 10mm hex and was several inches long so it's easy to cut off an inch or so and then it would fit like the KTM one. Sean
  5. That is the first I read of that. Have you a link to more info on this? I'll be looking more closely at those bolts from now on. Sean
  6. The RFS motor is a very durable design. The problem is that as the motor wears, it doesn't lose much power in the process. I would be willing to bet that a good percentage of failures is due to the owner not realizing the engine needed any maintenance because it was running strong right up until the failure. Have you de-smogged your bike and removed the exhaust restriction? Are you running stock gearing? Is it properly jetted? Those things will give you a lot of oomph. My buddy who rides a 525 comes over with his cousin's 07 525EXC. The thing is completely stock and he has about 2000 kms on it. At first I thought there was something really wrong with the bike because it was so gutless. I have a few big KTMs and I know how they should run. I had to yank on the bars to wheelie in 3rd on pavement! On my 525EXC, 4th gear roll-on wheelies are fun! Anyway, just to illustrate how much difference those things make. The one thing that makes the biggest difference IMO is the gearing. I think 14/50 or 14/52 is the best overall for the EXC transmission. Oh hell yeah. Sean
  7. Jetting could be lean but my guess is the exhaust is leaking around the flange/header. It is common on KTMs and some people have had good luck sealing it with high-temp silicone. You could try new springs too (or double them up) in case the old ones are weak. That may help keep the header tight against the exhaust flange. Sean
  8. IMO, the downfall of the SX (or MXC) for trail riding is the gearing. 1st gear is roughly equivalent to 2nd on the EXC so you need to gear it down via the sprockets to get a decent low-speed gear. But with only four gears, that kills your top speed in the fast trails. You can change/add gears from the EXC models to build a 6 speed transmission. Would be nice to have a lower 1st gear in the woods and two more gears on top for the fast stuff. The EXC flywheel will work but you would need to use the EXC stator and EXC ignition cover. Even shopping for used parts it's probably cheaper to buy a new flywheel weight for what you already have. If you think you would like to add the e-start or lights later on then I would recommend finding used EXC parts. The exhaust on your bike is a little less restrictive than the EXC/MXC models and IIRC it doesn't have a spark arrestor. I put a Pro Moto Billet SA on my SX and it didn't kill the power but it made the bike a bit quieter. Other mods I would do is pretty much standard for all of my EXC bikes. Case/clutch saver, skidplate, rear disc guard, full handguards, radiator guards, softer seat (I use EE tall soft) and a steering stabilizer. (personal preference, don't run one on my track-only SX) Sean
  9. LOL. An oil cooler is never a bad idea, especially one like the HT unit because it also increases the oil capacity, but to suggest that the oil is toast after 40 miles is absurd. I don't have an oil cooler on my 525EXC and it has over 12000 kms on it. (also street plated) It is not very often that a ride on it is anything less than 50 miles, and mostly trail at that. I can tell you from the coolant temperature probe on my TrailTech Vapor that my RFS bikes run cooler on the street than in the trails, much cooler. I change my oil about every 1500kms and the oil filters at every third oil change. Like offroadrider suggested, I would put a cush drive rear hub on it. Being a 450 crank spread is minimal and a cush hub would eliminate the need to upgrade the mains. If ever you need to split the cases it's a no-brainer because the bearings are about the same price as the roller ones but I wouldn't open it up just to do the bearings. Sean
  10. Jetting maybe? The 250 RFS is a little finicky. DAMHIK. To get my 525 started cold I put the choke on and give two squirts with the throttle. Fires instantly. Without gas, it will not fire. To get my wife's 525 started cold, I turn on the choke and push the button. Fires instantly. If I touch the throttle before pushing the button, it will flood, won't start and will need to be kicked. Like D1k says, maybe just the battery. It starts fine hot because it has been charging and has a little more punch but when cold it loses some power from sitting. Sean
  11. Haha. BTDT. "I'm sorry, is that your knee stuck in your mouth?" Mine is an 86. Same hole. Sean
  12. 14 000 miles and 500 hours? Wow! I got to 8000 miles and 280 hours before I needed to replace the rings in my 05 525. I whip mine pretty hard, it's street plated but sees mostly fast trail and also did some MX. I can only imagine the condition of the rest of your engine if you have run out of adjustment on your valves. If you have changed the oil and replaced the air filter regularly, there is a good chance that your bottom end may be fine. Personally I would split the cases and check everything if it was my bike. In the very least, you need to have the head rebuilt and you also need to replace the piston and rings. I would also replace the cam chain as well. I wouldn't even look at it funny before doing any of those things. Most of the work you can do yourself, least of all the disassembly and reassembly but the head should be sent to someone who knows them well like Dave Hopkins. Good luck. Sean
  13. I think you're right. The basket on my 525 was hardened steel now that you jogged my memory. The fingers on my wife's 250 EXC-G were grooved when I installed a Rekluse at about 30 hours. I remember it had an aluminum basket because I filed them down to be sure. Sean
  14. There's a used 2K2 stator for sale in the classifieds at KTMTalk. The seller is asking $50. I only mention it because it is the first thread at the moment. Sean
  15. Brand new is $245 list. (#4) If you don't have lights you can use #3 at $167 list. I would try finding a used one. I think they used the same stators until 2004 on the 2 strokes. Sean