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dirtr1der

02 WR exhaust cam mod

5 posts in this topic

OK,

Just adjusted the valves on my 02 WR. While in there, I did the WR/YZ exhaust cam timing mod (went from 13 chain pins between the cams to 12.) All went well, but now I'm wondering if I have to re-jet. Acceleration is powerful and hard hitting in the mid to upper range of the powerband, but I'm getting alot of popping and backfiring upon deceleration. Is this something that can be adjusted by adjusting the fuel screw a turn or two, or do I need to look to re-jet the pilot and/or needle position? The bike does not seem to be running lean or hot other than the backfiring upon decel.

Any advice would be helpful. Thanks.

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Have you disabled the ACV circuit? Also how good are your exhaust seals? Both will let fresh air into the engine/exhaust pipe and give you popping and backfiring. As far as jetting, you need to give more info so the guy's around your area can help out. Did the bike run good before, what is your current carb set up, single track or wide open, etc. I run a bit bigger main after the YZ timing mod . WR Dave

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Hi wr dave, I didn't realize that the 02 had the acv circuit. Does the 01 have it too?

Dirtr1der, I have also just done the cam turn, but really haven't had the chance to ride except for a cruise around the block. I had so much torque and mid range before that I'm really skeptical, I will just have to wait and see. I didn't hear any backfires though.

I suspect what could be happening is: When you turn the cam, it actually retards it so it closes later, letting the exhaust scavenge the air from the combustion chamber. After you let off the throttle, your unburned mixture is being ignited in your header, causing the popping sound.

Ive read a thread about this where Burned Said that its perfectly normal for a four stroke to do this, and some people actually over richen there carbs to compensate.

In doing this mod you probably are getting better air flow, but I suspect the popping is more related to the timing and if shes running really good I wouldn't worry about being over lean. But then again, with all them jets, it can always be jetted better :crazy:

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OK,

Just adjusted the valves on my 02 WR. While in there, I did the WR/YZ exhaust cam timing mod (went from 13 chain pins between the cams to 12.) All went well, but now I'm wondering if I have to re-jet. Acceleration is powerful and hard hitting in the mid to upper range of the powerband, but I'm getting alot of popping and backfiring upon deceleration. Is this something that can be adjusted by adjusting the fuel screw a turn or two, or do I need to look to re-jet the pilot and/or needle position? The bike does not seem to be running lean or hot other than the backfiring upon decel.

Any advice would be helpful. Thanks.

I would try setting the fuel screw/pilot jet, also raise the needle a clip and try that as well.

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I would try setting the fuel screw/pilot jet, also raise the needle a clip and try that as well.

You will want to do thes in that particular order and one at a time. Otherwise you will just end up confusing yourself unless you get very lucky and hit it first shot. The fuel screw setting will tell you if you need to adjust your pilot jet. If you find that your pilot and fuel screw settings are good then you can go to the needle. Hope this helps.

Josh

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