'09 450, losing power

11 replies to this topic
  • myoung

Posted November 28, 2010 - 09:29 AM


Well, I guess my streak of good luck with four strokes had to end some time. lol!!

So, yesterday I'm racing at Glen Helen and the track layout is really long, fast and we were using three of the big uphill runs, one of which was pretty steep. We were doing fifteen minutes and during the last two laps of my first moto, my bike felt like it was losing power. No noises, it didn't lock up, it didn't skip a beat other than feeling sluggish. It felt lazy coming out of the turns no matter what gear I was in and I was down shifting to second at the top of the steep up hill I was hitting in third or fourth a couple laps earlier. It was still pulling fine on areas that didn't put a load on the bike, though.

I checked the cam timing just in case that jumped, but it's still good. I rode it around the other track there before my second moto and it felt OK, but that track didn't have any hills I could check it out on. I didn't risk it in the second moto and borrowed another bike. Since then, I haven't done anything else.

Looking to gather thoughts, suggestions and ideas before I start tearing in to it. Don't want to take things apart I don't need to. If someone has experienced this and found their cause, I'd like to hear what your problem was. So far, I've had people thinking crank, piston, valves or carburetion. First on my agenda is to drain the oil and check for metal. Oil is new with an hour and a half of ride time.

  • grayracer513

Posted November 28, 2010 - 11:26 AM


Before draining the oil, check the level. If it hasn't used any oil, it's a very good sign as to the condition of the cylinder.

Most of the time, a loss of power as you describe it is a matter related to either the fuel or ignition system. It can also be an illusion. The soils at GH are fairly sandy, and traction falls off some during a race. Thinking back, did it just feel sluggish, or was it noticeably loosing ground to the other bikes in your race?

I would bet it's not a mechanical condition, but anything is possible. More likely borderline jetting, or an issue with the CDI related to timing. Something else you might check if you're running a spark arrestor is whether you blew a bunch of packing up against the screen.

Good luck...

  • myoung

Posted November 28, 2010 - 12:00 PM


I was able to stay with the guys in front of me in no load situations, but with loads like the up hills and digging my way through the deep loose turns I would lose ground. I still had power, sometimes. It was weird and something I hadn't experienced before without some kind of failure.

The oil level was good and the oil on the stick looked like I just poured it in. Hasn't turned brown or anything.

I'm tempted to believe it's not mechanical as well, and I think you might be on to something with the spark arrestor. I do have one in there and it could explain why it ran fine after I shut it off. If there is packing loose in there, it would have fallen down the pipe after the race. But being on the throttle the whole time during the race would have kept it tight against the screen. That might be my first order of business now. I was thinking it was about time to check the packing anyway.

I have been on the hunt for a good deal on an '06 CDI, maybe I need to kick that search into high gear. I just bought some parts to do some tweaking on my carburetor tune, maybe I'll find something amiss while I'm in there. I also just got the chain in to do my '06 cam swap, I can check the stator while I have it apart too.

I knew I'd get some good ideas I was missing here, thanks Gray. :thumbsup:

  • myoung

Posted December 08, 2010 - 08:24 PM


Well, I've got everything back together now. We'll see how it runs this weekend. It's sink or swim at the SRA GP at Glen Helen.

I couldn't find anything wrong anywhere, I'm at a bit of a loss as to what it is/was. I'm curious as to how likely it could have been a cam gear spinning. I noticed the exhaust lobe sitting slightly lower than the intake when on the timing marks. Not sure if that's normal or not, but it kind of looked like the '06 cam lobes were more even. Optical delusion maybe?

I changed out the cams and timing chain and I checked the coil and the stator while I was there. I changed the main jet and needle in the carb and checked all the passages while I had that apart. I checked the exhaust packing and it looks fine. I drained the oil and there's no metal in it. I changed out my clutch basket which was badly grooved, but I don't see that being the cause of my original problem. So far, nothing I've checked points to a problem. Only thing left I want to change is to go to an '06 CDI, just haven't found a good deal yet.

Maybe it was the cam, maybe not. I guess I'll find out this weekend.

  • myoung

Posted December 12, 2010 - 07:44 PM


Well, if any one is interested, I was at Glen Helen all weekend where I did a 45min. GP on Saturday and a two 15min. moto race on Sunday and it never skipped a beat. Maybe it was the cams. :thumbsup:

  • YamaLink

Posted December 13, 2010 - 07:37 AM


Good to hear it was resolved. So is your mind 100% okay with it or do you think about it now?

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  • myoung

Posted December 13, 2010 - 08:34 AM


I thought about it a lot the first lap of the GP. They used a lot of the main track for the GP including the big uphill and the deep loamy turns where I first noticed it. All the places the bike struggled before, it went through with no problems. Once that happened I knew it was working fine again. I'm just not 100% it was the cam, but nothing else I checked or worked on showed signs of causing a problem, so process of elimination lets me believe it was the cam.

That's the problem with not making one change and then testing it. I probably should have held off on the carb tune changes and the new clutch basket and just done the cams and tried it out. I had already done the others before I got to the cams, though, and noticed the exhaust lobe looked off.

Oh well, I'm happy it's running again.:thumbsup:

  • brentn

Posted December 13, 2010 - 09:00 AM


If a cam gear spun, a valve would have hit the piston and you'd have yourself a kaboom. Could have been electrical, maybe the TPS connection was wet, or came loose a little, or another connector for the ECU.

  • grayracer513

Posted December 13, 2010 - 09:15 AM


If a cam gear spun, a valve would have hit the piston and you'd have yourself a kaboom.

That depends on which cam gear slipped and how far. Not necessarily true.

  • myoung

Posted December 13, 2010 - 10:06 AM


If a cam gear spun, a valve would have hit the piston and you'd have yourself a kaboom. Could have been electrical, maybe the TPS connection was wet, or came loose a little, or another connector for the ECU.

I've also had people saying maybe the CDI got hot, but how? If it can get hot from just the bike running, I'd think it would have gotten hot again in a 45min. GP. None of my connectors were covered in anything wet, so I don't think that was it.

I don't really know that the cam was it yet. It could be a situation where all the planets aligned to create the problem on that one day, but it didn't happen again last weekend. So I dunno, maybe there is still something electrical that could fail again down the road. All I know is I couldn't find anything I could confidently point an accusing finger at except the possibility of a spun cam gear.

Trust me, I'm still second guessing whether I actually saw a difference in the lobe position. It just looked off, that doesn't mean it was. I would think any amount the human eye could notice would be a lot of change, like 10 or 20 degrees or maybe more. You'd think that would do some damage like you say, yet I never heard any noises and the bike never tried to lock up.

I wish now I had rigged up a dial indicator when I was swapping the cams to verify if my suspicions were right and I knew for sure. I guess if I got a wild hair going I could throw the old cams back in and take some measurements.

In the mean time I'll remain cautiously observant to see if it happens again. Next race is this weekend and I won't be changing anything.

  • myoung

Posted December 13, 2010 - 10:46 AM


That depends on which cam gear slipped and how far. Not necessarily true.

Hey gray, I'll explain how I got to thinking I had a cam issue.

I'll use this image........

Posted Image

......... to reference my explanation because it's what I dug out when I noticed the lobes looked different. I had printed this back when I did my cam swap on my 426 and I figured the 450 lobes should be in about the same position. Maybe that's wrong and I'm going down the wrong path thinking it's a cam.

In the pic that shows the lobes, they look pretty evenly splayed. When I was looking at the lobes on my old cams, they didn't look even. Either the intake was slightly higher or the exhaust was slightly lower. I couldn't really determine for sure which, but they didn't look even like these do. I thought I hadn't rotated them around enough, but I checked the timing marks over and over and they still looked off. I was kind of leaning toward the exhaust looking like it was sitting lower from the way it looked compared to this pic, but when you're eye balling something it's anything but accurate. When I put in the new cams, they looked more even like the pic.

I also changed the chain, but I didn't think the old one could have stretched enough to cause an easily seen difference in lobe position after 63 hours. What do you think?

  • grayracer513

Posted December 13, 2010 - 11:28 AM


I wouldn't think chain "stretch" (which is actually the accumulation of pin wear) would have figured in that amount of time, either, but I've seen low hour chains get stiff, and that will cause a timing failure.

As to the appearance of the lobes, you can't really go by that picture, which is of a 426 using the cam from an '03. One of the differences between the earlier YZ's and the later ones is the cams, but it is the timing, not the grind profile, that differs. The offset of the lobe centers is what is changed and if you were able to look very closely (or use a degree wheel), you might see that the lobes of the older engines are more widely opposed to each each other than the newer engines, in which the lobes would appear to be standing more vertically. It's a pretty small difference, though.

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