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pobit

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  1. I have been riding the bike the past week and my opinion is the same as yours. The bike now has plenty of power but hits a little too hard at off idle for good throttle control in slippery or rocky conditions. I called Tom Morgan on Friday and asked him if he thought the higher compression was causing this. He did not think that the higher compression was the problem. He said the new head is just using all the fuel and making more power. He suggested using leaner jetting to reduce the hit. Specifically the pilot and needle straight diameter. Saturday I spent most of the day testing suspension settings for Sundays race. All I had time for jetting testing was to install the N3CW needle in the #3 clip and go race it. This is 1.5 clip positions leaner than N3EW#4 I was using. I raced the bike today at the Millville MN Hare scrambles. This is about 1000 ft elevation with temps in the low 60 degrees. I got third in the hole shot with about 40 riders on the line. I finished 1st in SS A. Millville is the location of one of the outdoor motocross nationals. They use most of the national moto track and the surrounding hills and ravines for the race. It is a difficult race. There are several very steep rocky hills and wet rocky ravines where you need good throttle control. I did struggle in the slippery parts and had to be very careful not to twist the throttle too fast in these sections. I am going to have to find smoother jetting. One interesting thing I discovered during this race is that the X power valve setup allows you to stretch gears without having to up shift. Normally with a YZ250, you have to upshift in the upper revs because it causes the rear suspension to start skipping and bouncing. I did not think I liked the X power valve but now I think I see a benefit from its high RPM smoothness. By the end of the day as a got more trust in this RPM range, I was using this part of the power band more. It is a weird feeling reving that fast on rough ground, but it works. If anyone has jetting suggestions for smoothing out the off idle hit I would sure appreciate it. Thanks, Dave
  2. pobit

    Cambridge Minnesota Harescrambles May 8th

    If anyone has questions about the race give me a call. I will be at the track from now until Monday. Dave 612-940-2833
  3. First I would like to thank everyone that has helped me on this thread. I did send the head out to Tom Morgan to have the squish tightened and the compression raised as TMX recomended. This made a big difference in the power delivery and jetting. Before the head was cut, I could not get a clean torquey pull on the bottom. Also the mid range was not pulling hard enough to stay ahead of the jetting and would go lean and then feel weak. I like to run rich jetting to get torque to the ground when accelerating. The new head allows me to run a 48 pilot, N3EW#4 175 main at 1000 feet, 70 degrees. With this jetting, the bike puts the power to the ground without a lot of wheel spin. I am now very happy with the bottom and mid pull. It still has the X's smooth power. It is just a lot stronger and you can twist the throttle for more boost when you need it. The top end still goes flat but now I can at least race the bike and be competitive with the KTM's. The next thing I am going to try is the power valve mod posted above by 218 to see if I can get some top end boost. Thanks again for the help. Dave
  4. Did you notice an increase in over rev when switching from the X muffler to the Turbine Core 2? I am thinking the stock muffler may be part of the reason it will not rev out. I would like someone to test my theory before I buy a muffler and find out I was wrong. Thanks, Dave
  5. pobit

    Cambridge Minnesota Harescrambles May 8th

    The C class is a very easy fun course to ride. The A and B class get a little longer and harder course but still nothing the average dirt biker can't handle. No big jumps on the MX track. This years course has a really nice mix of a sandy moto-cross track, grass track, fast fields, beautiful flowing single track, a snail, a few long bridges over the water to an Island and 5 miles of brand new single track. This course has just about anything you would see off road all in one race. It is an excellent course that will be a lot of fun to ride. I just mileaged the course last Sunday and it is 10.1 miles long for the A's and B's.
  6. I have found above 5000 feet pilot jets have to start getting bigger because the difference in air pressure is lower. Your creating less vacuum so the hole in the pilot jet needs to be bigger. The best way to understand the effect both those needle end tapers have on the mid to top is to remove the main jet and ride it. You will find that you can ride the bike with the N3EW almost the same until you get near full throttle. With no main in the carb, it is easy to feel the difference in the two end tapers. Try it. After that, you will be able to tell the difference the main jets make because you will have a good feel for the needles. If your worried about getting too lean on the main, do a wet oil line test at full throttle and pull the pipe to make sure the spent exhaust is not coming back into the cylinder on the reverse pulse. Dave
  7. ] Attached is a flyer for one of the best examples of a MInnesota Harescrambles. 10 mile long course with 5 miles of brand new single track. More info at www.norsemanmc.org
  8. I may try the suzuki needles in the YZ. I didn't like them in any of the KTM's I tried them in. Too lean at off idle and then make the motor go flat with the rich end taper. What I like about the stock needle series is that rich spot at off idle that everyone complains about. It does make the bike stutter when blipping the throttle or just trail riding, But when under a load and accelerating, it give good torque and helps control wheel spin to get power to the ground. I also like the thick end taper for getting over rev. The one thing I do not like is the motor can get lean and struggle to accelerate if the RPM's are not up under a load. The guys running the stock needle in clip #2 at sea level are missing out on a lot of mid range torque when run in that low of a clip position. Currently I have 48 pilot, N3EW #3 and 175 main. This is better than stock but I know I can get better yet. I just have to wait for the head to come back. What I think will work is larger diameter straight sections in a higher clip position with smaller mains. Something like N3EJ #3 for trail riders, N3EK #4 for racers. Once I have time to jet, I will post my results. Thanks, Dave
  9. I may try the YZ power valve spring as you suggest. I set the KTM250XC I raced last year power valve to open quicker with a lighter spring and more preload and then ran a leaner main to get an upper hook with over rev on that motor. That may work on the YZ250X too. This thing is pretty lazy on top. What I have tried so far is using the stock needle taper with a smaller main to do the same thing. The problem is the motor does not have enough power to spool up and take advantage of going lean in the upper revs when under a load. I am hoping the head will help with this. Once I get the head back on, I will post my jetting results and see if this will work. ​Thanks, for the help. Dave
  10. I talked to Tom Morgan today and sent the 2006 YZ250 head off to him in the mail. Very helpful guy. Tom is in Wisconsin and I am in Minnesota so with a little luck I will have the head back by Friday to do some more testing. Thanks for the feedback on the 99 head. That is the type of info I was looking for: Real world testing.
  11. I raced a 2014 KTM 250XC last year and this bike is not as strong as the KTM. I have raced YZ250's in the past and they had plenty of power so I know that the motor can be stronger. I am racing A class and this bike does not have enough mid power to hang with the KTM's I will be racing against. I like the power delivery of the X. It just needs to pull harder for racing. Thanks, Dave
  12. I read that thread but it does not have the information I am looking for. I want to know what size to make the head and how it affected the power. What size are you going to cut the YZ250 head to? I also have a stock 21cc 2006 YZ250 head on the bench ready to cut. I Just need to know what size to make it. Thanks, Dave
  13. I have a 2016 YZ250X I am going to race in A class Harescrambles and enduros this year. I have about ten hours on the stock motor and have noticed three items I would like to fix. First the bike does not jet clean. Second, the bike gets poor mileage. Third, the bike does not pull hard from mid to top. Cutting the head to tighten up the squish should solve the jetting and mileage issue. The question I have is this: Has anyone modified their head on a 250X yet and how did it work? Specifically I would like to know if you raised the compression to increase power and what bowl size you chose. The stock 250X head is about 23.5 cc. A stock YZ250 is about 21cc.
  14. I need to replace the left radiator on my 2000 WR400. What other years and models will fit? Thanks, Dave
  15. pobit

    2009 YZ450F Review

    I have an 08 and I found the rebound is too fast on both ends. The bike pushes back at you and makes it feel harsh. I ride A class and run the fork compression dampening at 13, rebound at 6. shock sag 102mm compression 9, High speed 1 3/4, rebound 7. Dave
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