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mycr500

Question: Just changed to YZ cam in my WR426

12 posts in this topic

I just completed a cam swap in my 2001 WR 426. Changed to the YZ450 cam with the compression release.

I noticed a couple of things.

The bike virtually would not start until I changed to YZ timing (eg blue wire cut).

I seems to bog and often dies from a low idle, the idle speed that I had set with the stock cam. This is if the throttle is moved to wide open. Setting the accelerator pump duration longer did not solve this, it only made the bike "run on" longer. So I put the duration back to about one half second or so. Changing the idle mixture helped a bit, but I still think I have to run with an idle speed faster than I would like to for riding on slick rock and knarly trails.

Has anyone else experienced this?

Also, does anyone have experience with their gas mileage? Did it go down noticably with this mod?

Thanks, Paul

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Cutting the blue wire cancelled the 'in neutral' reduced ignition voltage and lowered rev-limiter, to make it easier to start. You need to cut the grey wire, which will give you 'YZ' timing, while preserving WR's 10500 PRM rev-limiter (YZ 11500 RPM).

The YZ450 cam should be installed in 'stock' position, with 14 chain pins betwen the timing marks. Also, have you checked your valve clearance?

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Cutting the blue wire cancelled the 'in neutral' reduced ignition voltage and lowered rev-limiter, to make it easier to start. You need to cut the grey wire, which will give you 'YZ' timing, while preserving WR's 10500 PRM rev-limiter (YZ 11500 RPM).

The YZ450 cam should be installed in 'stock' position, with 14 chain pins betwen the timing marks. Also, have you checked your valve clearance?

I think I wrote this wrong. I cut the wire that is in the 2 pin connector from the CDI unit. It would be grounded until the wire is cut. I see a blue wire from the 6 pin connector that according to the manual goes to one side of the throttle position sensor. I did not cut this one. Does cutting this one increase the starting voltage? Interesting if it does. However, would the bike run without the TPS circuit complete?

I changed the valve shims. But I could have done it incorrectly. I did the 14 pins. I think the cam is right or I doubt the bike would start or run at all?

Thanks for your reply.

Paul

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The bike will start with the cams incorrectly timed and will cause all the symtoms you are talking about, be sure to check your timing with the tensioner in place, my bike gets nearly 200 k's to the tank now and it roll starts when i am walking next to it, tooooo easy.

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I had similar problem with the mod. Once warm it would start fine but very hard when cold. I could not get the cams to line up per the PDF file. The intake was 1/2 tooth off. I tried 13 and 14 teeth, intake cam 1/2 tooth clockwise, 1/2 tooth counter clockwise. Same results on all tries. Had it apart 6 times and was ready to go back to the 426 cam. Installed a new cam chain last night, everything lines up perfectly. 40 degrees, one kick and it started. :) I only have around 1,000 miles on it and was very surprised that the chain had stretched that much. At TDC the intake punch marks should be very close to 9 and 3 oclock, if not a new chain may be in order.

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I had similar problem with the mod. Once warm it would start fine but very hard when cold. I could not get the cams to line up per the PDF file. The intake was 1/2 tooth off. I tried 13 and 14 teeth, intake cam 1/2 tooth clockwise, 1/2 tooth counter clockwise. Same results on all tries. Had it apart 6 times and was ready to go back to the 426 cam. Installed a new cam chain last night, everything lines up perfectly. 40 degrees, one kick and it started. :) I only have around 1,000 miles on it and was very surprised that the chain had stretched that much. At TDC the intake punch marks should be very close to 9 and 3 oclock, if not a new chain may be in order.

I know the intake cam is in the same position as before because I put a tie wrap on it. The exhaust is 14 pins away. The bike has less than 2000 miles on it, but I suppose the chain could be stretched, I will check this. I don't understand what you mean about 1/2 tooth on the cams? Don't you have to go one chain tooth one way or the other?

Thanks,

Paul

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The bike will start with the cams incorrectly timed and will cause all the symtoms you are talking about, be sure to check your timing with the tensioner in place, my bike gets nearly 200 k's to the tank now and it roll starts when i am walking next to it, tooooo easy.

The bike does start fine now, it just wouldn't with WR timing. I got 40 mpg with the WR cam, so I think your results are similar.

Thanks, Paul

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I don't understand what you mean about 1/2 tooth on the cams? Don't you have to go one chain tooth one way or the other?

Yes you do have to go one full tooth. My chain was stretched enough that the intake would not line up correctly, could not get the punch marks parallel to the head. With the new chain they are right on. As the chain stretches the cams will line up slightly clockwise from perfect. In my case this was about 1/2 tooth.

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Be sure that you are lining the cams up correct per the LOBES and the cylinder is at TDC by the timing mark on the flywheel.

If you have an aftermarket flywheel such as the zipty racing, remove it to find the factory timing marks! Been there when I bought the bike and never reinstalled it.

Also a new cam chain and tensioner is a good idea on a bike with some miles on it (install the '03+ tensioner -- shorter design). If the tensioner is weak, then you have a posibility of having the cam slip on the chain for sure.

Also, dont cut wires! take your time with a screw driver and disconnect the wire from the plug housing. Post back if you need a copy of that PDF with pics of the cams installed

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Hey TC how hard is it to change the cam chain?

I already have the rotor puller from my baja designs kit?

Do I need anything else?

How long did it take you?

Thanks

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Are you saying that cutting the blue wire raises the rev limiter? I hadn't read this before.

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Hey TC how hard is it to change the cam chain?

Once the flywheel is off its not a big deal. The chain rub blocks are on both sides. Remove the two bolts on the bottom on the one towards the rear of the bike and you get enough room to operate. The front block won't come out unless you remove the head. Its very, very tight but the chain can be replaced without removing it. A little prying on the front block to gain a little more room. If I were to do it again, I would order a head gasket with the chain and remove it. Either way a 15-30 minute project.

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