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      HOW TO: 4-STROKE PISTON REPLACEMENT DONE RIGHT!

moleson10

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About moleson10

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  1. Sounds like a nice setup. I've got a 2013 with similar mods. I ride vet track mostly but some off road too. Oversize front rotor and SS braided brake line really improved the braking. My other bike is a KTM so I was spoiled by good brakes. Off road it's not as important but on the track it is. As some have said, going taller (48) can sometimes help in the tight stuff because you can actually use first gear. But if it's really technical that may not work because you need a really low gear. The mx bikes can be tough to setup because their first gear is so tall.
  2. Great thread and boo yah!!!!! to the OP. Way to step up. You are doing up your new ride right with the FMF 4.1 and black rims. Add an oversize front rotor, steel braided line and suspension lowering and you'll be riding my ideal FX. I am wrestling with the same questions many of you have. My current rides are a 09 KTM 250xcfw with a 290 BB and a 2013 YZ250F. I want to upgrade my KTM to either the FX or a new KTM 250F. I'm very interested in others experience when they have done the same kind of upgrade (older carb'd 250F to new FX). Keep those posts coming.
  3. MXA did a very thorough review of the FX in the May edition. I looked for it on-line but didn't find it. If I do I'll post it. Overall they liked the bike and felt it was raceable in stock form. They had the usual quibbles with the front brake and thought it was on the heavy side but applauded Yamaha for a fine effort. They also explained why the bike feels so tall. They were puzzled by the seat height because it was noticeably higher than the 250F they had for comparison. Since they are moto guys they were just going to swap the shock out for one from the F model. But they talked with the Yamaha guys and learned that Yamaha had to jack up the back end 15 mm and reduce the shock travel to make room for the battery. If they put the F model shock in it the rear tire would hit the fender!
  4. You'll be happy with the YZF. It's what it was designed for. I tried riding my ktm 250xcf-w at the track a couple times and learned pretty quick that wasn't going to work. So I bought a 2013 yz250f and love it. The ktm is still much better at offroad. I'm 58 and just started riding track a few years ago. The vet track is fun but the big boy track is still scary (Cahullia Creek MX in Cali).
  5. I read recently that big bore 250f requires leaner jetting. This seems counterintuitive until it was explained (in MXA). The bigger bore engine draws more air which means higher velocity in the carb venturi. Higher velocity pulls more fuel and therefore the jetting can be leaner and still provide the correct amount of fuel. Makes sense when you think how a carb works. If there isn't much air going thru it there isn't much vacuum to pull up the fuel so you need bigger jets to compensate. I noticed this when I did my KTM big bore. Prior to the upgrade it would bog and stall at lower RPMs. After the BB it ran much better down low.
  6. sgrimmxdad For the record, can you clarify is the an F or FX model. I thought it was an F but in your post you said "it will not even crank" which sounds like an FX.
  7. Give us a ride report after. It's a good bike that just needs some simple mods to be great. In stock form the muffler is overly restrictive. Get an FMF or equivalent and you'll pick up a couple horses. Put on an R&D powerbowl if you have bogging issues. Some do, some don't.
  8. Good thread on an interesting subject. Old vs. New. Both are great but out of the box, the new bike is clearly better. Would the new motor (with the head reversed) in the old chassis be even better hmmmm....... The shift stopper is a big deal and should be replaced under warranty on a new bike. Sounds like you can do it yourself too if you had to. The impeller is less of a concern but should be fixed too.
  9. Yea!!! I love a happy ending.
  10. I'm interested in how you end up liking your FX. i'm torn between it and the 350 xcf. There's a lot of reasons I'd prefer the FX, suspension being one of those but I'm put off by the heavy feel. Just lifting if off the stand it feels 20 lbs heavier than the 350xcf which is in the same store. Reminds me of my old DRZ400. I'm not sure why it feels so heavy because it's really only 3 or 4 lbs more than the xcf. My current bikes (13 YZ250f and 09 250 xcfw) both feel like mountain bikes in comparison. Please keep posting your impressions. Thx
  11. If you are going to buy a used 250f mx bike, the yzf is the one to buy. Best reliability of all the brands. Doesn't mean it can't have issues but as swappa said, if it starts right up, runs well, doesn't burn oil and doesn't have a lot of engine noise (cam chain slap, etc.) you should be fine. Make sure the transmission has all the gears and clutch doesn't slip too.
  12. Good point, it could be too rich since the OP mentioned the original owner put in a larger jet for the new pipe. Usually a new pipe alone doesn't require a re-jet so that may be the problem. I assume we're talking about the main jet so after checking for intake leaks I'd put the stock main jet in and try that. I like your use of the enrichener and hot start. That's a good idea. Not sure if the OP will follow that but it's a really good way to quickly determine if the problem is too lean vs. too rich.
  13. There's something wrong with the fuel mixture. These motors are not so high strung that they won't run well at partial throttle opening. It sounds like you have a lean condition at mid throttle. Not knowing anything about your setup it's hard to give good advice but here's what I would do first. Don't assume it's the carb right away. A lean condition could be caused by an air leak between the carb and intake port. Check your intake manifold for cracks or leaks around the gaskets. Make sure the clamps are tight. If all that checks out then its FCR time. Get a manual or look up the stock jetting/needle info on-line. Compare what you have to stock. You shouldn't be too far from stock unless you live at 10,000 feet. If your main jet and needle are in the ballpark. Try raising the needle one notch. That will richen your mixture at mid throttle. If that doesn't help you may need to get an expert involved. Don't give up on the bike just because its not tuned right. Once you get that resolved I think you'll find that it's a great bike.
  14. Gaz, I'm surprised the trail version of the yamalink only got you 1/2" lower. They claim 1.5" on the website. Did you increase the pre-load when you installed it? Shred, did you get your new bike from motoplex? They mentioned sending a new bike to the suspension shop, I wonder if it was yours? I'd be tempted to do the same thing if I buy one.
  15. After reading many posts and comments about how tall the new FX is I decided to find out for myself. Like a lot of you I'm super excited about the FX but concerned that it was significantly taller than my current ride and the competition. To settle it I went to my local dealer who also sells KTM. They didn't have an FX so I used the WR. They are supposed to be the same. Here's what I found. First my current ride is a 2009 KTM xcfw. Stock seat height is 37.5". 2015 YZ250WR - 37.75" 2015 KTM 250 xcfw - 37.5" So why all the fuss about how tall the FX is? I think its because the seat, and the overall bike, is quite a bit wider at the low point of the seat. When the sales guy and I looked at the KTM we both thought it would be a lot lower than the FX. But the tape doesn't lie.