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mlynn450

did 06 yz 450 cam swap in 07 wr450. Jetting question

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I did the cam swap and set the timing marks according to the wr manual and have double checked everything its spot on. Problem is I have lost the crispness in throttle response.I was expecting a little off the bottom, but there doesn't seem to be much of a hit anywhere. It starts right up first kick and even starts with the e-start. Could this be a jetting issue? I have all the free mods, ap is good with a #45 leak jet, nflr needle,48 pilot and 170 main merge ap spring,06 yz exhaust. Is this normal. Any suggestions would be appreciated. It's the exhaust cam only.

Edited by mlynn450

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Is your airbox and exhaust modded to support the additional flow? I've been told by several in the know that a cam only doesn't need jetting changes but to take advantage of the yz cam ur exhaust and intake must be opened up some. Your fuel screw might need adjusting out a bit too.

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Yes the air box is opened up and I'm Running a full 06 YZ exhaust and the fuel screw did need adjustment, it just had a little popping on deceleration. I'm very unimpressed with the results of the swap so far.

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I put both YZ cams in mine as well as a high compression piston. 08 YZ exhaust and airbox lid cut right open with ebatt. I found jetting sayed pretty much the same but is a little more finicky to weather / elevation changes. She has really crisp throttle response, strong and smooth through the range with no real hit but she definately has alot more guts than before. My estart works less than half the time though. I find if you tune it to estart you are too rich off the bottom. I run a 45 pilot, fuel screw cranked in in the summer and opened right up on the cooler months. It's VERY sensitive to the fuel screw now.

I ride between 500 and 4000ft elevation generally.

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I'm not sure about the number of links, but All the timing marks are lined up spot on. I read somewhere on here to set all the marks according to stock settings in the manual. Anyone know if this is correct?

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I'm not sure about the number of links, but All the timing marks are lined up spot on. I read somewhere on here to set all the marks according to stock settings in the manual. Anyone know if this is correct?

Go by the timing marks, if they all line up you're good on the timing.

Like I said I would try leaning out your jetting a bit. I get more popping on decel with a rich pilot then lean with the ACV in this carb. I also run a 168 main, GYTR needle 3rd clip from the top.

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I have a 45 pilot and a 168 main. I'll give that a try and drop the needle one notch. I have the ACV disabled in the closed position. I really enjoy working on these carbs:foul:

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I have a 45 pilot and a 168 main. I'll give that a try and drop the needle one notch. I have the ACV disabled in the closed position. I really enjoy working on these carbs:foul:

ACV? Racking my brain.

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I'd count the links between the timing marks and post the number. The number of links between marks is different from wr to yz cam.

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I just got things tore apart again and there are 13 pins between the marks and the timing marks are lined up spot on. Is 13 pins correct? I'm also leaning out the jetting as per Tribalc. I'll let you know how it works . Thanks everyone.

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I just got things tore apart again and there are 13 pins between the marks and the timing marks are lined up spot on. Is 13 pins correct? I'm also leaning out the jetting as per Tribalc. I'll let you know how it works . Thanks everyone.

The WR timing is 14 pins and YZ with both cams is 13 pins. I believe the only difference in timing is with the exhaust cam so 13 pins should be right.

That said pins are just a reference and shouldn't be used to time. It's all about the dots lining up as chains can be stretched, etc. If all your dots are in the 9, 3 and 12 oclock positions when at TDC you are timed correctly, which you indicated they are earlier.

Let us know how it works with the leaner jetting, you may have to play around a bit. If you pull the boot on the carb on the intake side and remove the hot start, then loosen the other boot you can rotate the carb enough to get at the pilot and main. Needle you can get at if you remove the motor mounts.

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I ended up dropping the needle 2 notches to the 2nd notch ,45 pilot , and 168 main, fuel screw 2 turns out. Very crisp and responsive again. Test ride was on my road. Can't wait to go for a real ride. Thanks everyone:banana:

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W.T.F. is the ACV???

Air cut off valve. Richens the circuit on decel to prevent popping.

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The ACV is the air cut off valve. It doesn't have anything to do with the air mixture screw. This valve automatically lets more fuel threw and helps prevent that popping you get during deceleration. I don't know the technical details about how it works, but it does seem to be easier to dial in the fuel screw with it disabled. Back in 07 when I got this bike and was learning about the free mods I came across a thread about disabling the ACV. Made sense to me so I tried it and found I wasn't messing with the fuel screw nearly as much. . I disabled it with a spacer in place of the spring.

Edited by mlynn450

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This is new to me and I've been riding and working on these things since they came out in 98.

Where is this ACV located?

Thanks much, John

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Go to www.thumperfaq.com scroll down to free mods and then to air cut valve. It's a good explanation on how it works and how to disable it if you want to try it, Also good picture of it.

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