Hi Ya, First up I just wanna say a couple of friends put me onto this site a few weeks ago and I have been lurking here since then and I have to say hats off to everyone for such an awesome online community. Now down to business. I own a 2001 WR426F, and have owned the bike for 10 months now. It was bone stock when I bought and I have gradually been building it up as an Enduro race bike. I finally bit the bullet last week and had the YZ450F Cam installed. I am not overly technically minded and I don't have the best collection of tools at the moment so I decided it was probably best to pay someone who knew what they were doing to install the cam. The local Yamaha dealer flat out refused to install the cam for me . The local Honda Dealer agreed to install the cam (they apparently have an ex-Yamaha mechanic working for them which made me a little more confident). I even gave them my workshop manual and the installation instructions off this site to help them along. I dropped the bike in to have the cam installed and valve clearances re-set and picked it up the next day. They told me it took them 8 hours to do the work ($690 Australian ) and that they had to rejet the bike. I almost fell over backwards at the price. I took the bike out for a run and it just didn't seem right, the midrange seemed really flat. Then after about 20 mins of riding the bike started spluttering and losing power under acceleration, almost like it was running out of fuel. I shut the bike down, gave it a look over and then started it up again. The bike went fine for another 10 mins or so and then did exactly the same thing. I rode the bike back to the bike shop and told them what was happening. At first they tried to blame the cam itself saying that it was probably incompatible, but I told them that quite a few people has successfully performed this mod (right guys?). Unfortunately, the mechanic that actually worked on my bike was not there, so a different mechanic went to work on it. I sat there for 3 hours while they messed with the jetting, took the bike out, came back, messed with the jetting some more etc.... And at the end of it all they wanted to charge me even more money, but I flat out refused. So I took the bike out again and it seemed to go fine for the first 20 mins or so and then the same thing started happening - only this time it seemed worse - sputtering, no power and some popping from the exhaust . I nursed the bike home, shut it down, let it sit for 15 mins and then took it for a run a round the block and the problem is still there. I really don't want to ride it in case I am doing some sort of damage to it. Now I am at a loss what to do. If I take it back to the bike shop, I know they will blame the YZ450F cam as they tried to blame it the first time I took it back. Since they spent hours on the jetting, I am starting to wonder if it is really this (unless they didn't really know what they were doing). I live in Canberra Australia and we are at 1888 feet altitude (I know this because I get flying lessons on the weekend ) . The guys at the shop said they put a #175 main jet and a #45 Slow Jet in. I'm guessing everything else is stock. I will be the first to admit that I don't know a lot about jetting, but maybe this will help you guys try ad give me some suggestions as to what the prolem might be. The bike ran like a dream before I had the cam installed, but I suspect the cam itself isn't the problem, but the work that these guys did on it. Given the amount of money I have already spent I don't really wanna go back to the the dealer until I have some suggestions as to what it might be (other than jetting). Apologies for the long winded e-mail, but I guess the more info I give you guys, the easier it will be for you guys to help me. Oh, and the only other engine mod the bike has is PowerNow. The exhaust is a stocker (next upgrade ) Any advice you guys may have would be much appreciated.