wr 450f with yz 450f exhaust cam installed

13 replies to this topic
  • fried

Posted July 03, 2008 - 07:27 PM


I have a 2005 wr 450f. I installed a yz450f exhaust cam, the bike starts great with the kick starter but with the electric starter it does not. The engine seems to crank over fine but will not hit until the throttle is cracked open slightly. The funny part is you must leave the thottle closed when you first start cranking the engine and then while it is cranking crack the throttle. If you crack the throttle open first and then hit the starter button it will not
start and sometimes will kick back. So in order to start the bike with the electric starter I must use the above described procedure but it cranks a long time before it starts. I am wondering if anyone out there has added the yz cam and had similar problems. I think it is possibly a jetting issue , but was hoping someone may have run into this before.
thanks fried.

  • tweav

Posted July 03, 2008 - 08:07 PM


yes this is what happens when you install a yz cam . the yz cam dumps more compression then the wr because it hit the decompression pin sooner . I have a yz cam in my 07 wr . it is harder to ez start but I can kick it easier. You could take your bike and get it jetted it does start much easier then


Posted July 04, 2008 - 12:01 PM


I got so frustrated with this issue that I put the stock WR cams back in... BUT, before I did I put some time and effort into jetting and while not to the degree I used an O2 sensor or dyno I felt I had it pretty good and it still would not start with the button :p

Like tweav said, the OEM YZF cam is going to have a taller decomp pin and will dump more compression, factor in the fact that the WR's starter is slow and you have a situation where the motor apparently does not build enuf compression to start.

I admittedly like the performance gains I got with the cams but in hindsight, I wish I had gone with an aftermarket cam built specifically for the WR:prof:

Good thing now though is that my jetting is spot on, I've done the blu/wht wire mod and my WR starts so f'ing fast with the button it's ridiculous... as good as any other husky or ktm I've seen, it's like instantaneous and is still winning races despite the lack of the YZ cams :thumbsup:

  • MaxPower

Posted July 04, 2008 - 01:40 PM


[COLOR="Green"]I installed the YZ cam in my 04. Other than using needing the hotstart pretty much everytime the bike is warm, the cam is the best thing to happen to my WR motor. The YZ cam is designed for the WR motor,since the WR motor is a detuned YZ motor. Maybe I got lucky with the jetting.I have the oring thingie in the carb along with a Dr D silencer. I love my bike.I wouldnt ride it without the YZ cam.[/COLOR]

  • tweav

Posted July 04, 2008 - 08:05 PM


the decompression pin on the yz is not taller I mic'd, it is advanced so it opens the valve a few degrees sooner . my bike starts fine but it is not as ez as it was . if I just choke mine and do nothing else it start almost instantly . if I don't choke it it's kind of hit or miss . I never use the hot start at all. My wr does run better with the cam . but I still want more power . last time on the dyno it was at 51.2 hp it's not bad but It's not as much as I'd like.

  • MaxPower

Posted July 05, 2008 - 05:40 AM


[COLOR="Green"]I would be happier if I could lose 20 lbs off my WR rather than have more power

I forget how fast my bike is sometimes until I ride someone elses bike


Posted July 05, 2008 - 11:20 AM


the decompression pin on the yz is not taller I mic'd, it is advanced so it opens the valve a few degrees sooner . my bike starts fine but it is not as ez as it was ..

You're right, advanced, not taller.

There are so many different experiences with this mod, I just happened to end up on the bad end of the experience spectrum... :thumbsup:

One thing that you can be thankful for fried is that you have a steel framed bike and if you choose to do a lot of jetting combos, it will not take near as long as those of us with Al frames :p

I would start with your pilot, if you go to the jetting forum there is a sticky on the top for checking your pilot setting using the fuel screw, it's really useful:thumbsup:

Good luck, I hope you get it to point you are happy with it:ride:

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  • MountainMax

Posted July 05, 2008 - 02:10 PM


You want to buy a stock cam? If not, what I done, was just play with the jetting and it will start good.. not great, but good enough.

  • beezer

Posted July 07, 2008 - 06:25 AM


I run a 42 pilot jet and a Merge adjustable leak jet and it starts much easier but when I start it cold I kick it. It fires first kick then.

  • tweav

Posted July 07, 2008 - 04:08 PM


I run a 42 pilot jet and a Merge adjustable leak jet and it starts much easier but when I start it cold I kick it. It fires first kick then.

that's interesting . I also run a 42 pilot and a rd powerbowl and I can kick it the first try , or if I choke it with no throttle and the ez button it fires right up.

  • beezer

Posted July 08, 2008 - 08:12 AM


I stole the 42 pilot and adjustable l/j idea from you Tweav.

  • fried

Posted July 19, 2008 - 07:08 AM


Thank everyone for the replies to my problem.

  • fried

Posted July 19, 2008 - 07:26 AM


I have a 2000 ktm 520 with a rattle noise in the engine. when you pull the clutch in the pitch of the noise changes. also when engine is cold the clutch
is grabby after it warms up it seems to engage properly. I pulled the clutch cover off and inspected and did not find anything broken or anything that looked funny except the inner clutch hub had some groves wore into it, so I filed the grooves smooth and put it back together. I also noticed that the starter clutch seems to turn hard. Has anyone run into a similar problem on one of these ktms ? thanks for your input

  • grayracer513

Posted July 19, 2008 - 08:56 AM


Comparing any exhaust cam from a '03-'05 YZ450 (5TA-12180-00-00) to the cam for an '03-'05 WR (5TJ-12180-10-00), the lobe profile is exactly the same. The difference in the two is that the YZ cam is pressed into the sprocket in a different position so that the timing is more retarded, biasing the cam's effective range to a higher RPM. The reason the YZ decomp pin is retarded from the WR's is to compensate for that difference, so that the valve is lifted and reseated at about the same time.

A good many early (pre'06) YZ450's start better cold with the throttle lifted very slightly off idle, so I don't find that unusual, but it seems to me that you should be able to get it to start by working with the idle jetting.

Then again, with YZ timing, the engine will not want to run as well or as stably at very low speeds, and the e-start does actually turn the engine over more slowly that the kick crank does, so that could be part of the trouble, too.


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