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WR450 jetting help

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HI everyone,

I'm having some real issues getting the first 1/4 of throttle to work right. Here is some back ground to start.

05 Wr450 (Used for motard)

DRD Pipe

YZ cam

Holes cut in side of the air box

More holes in other areas(breathing close a yz now)

Smog stuff gone

Plunger thing on the side flipped over.


168 main

JD Needle 4th clip

42 pilot

Alum fuel screw.

Riding at 0-3k elevation.

From about 1/4 to WO the bike seems good when a new plug is in the bike. The pipe though looks really black and the back of the license plate is pretty black as well. Anything under 1/4 is bad when riding. The bike will rev fine in neutral with no miss or hesitation. In gear riding it surges bad until 1/4 throttle. when rolling back on the gas from deceleration its poping and stuttering. In fact it pops a lot in general as if it were lean but the pipe looks rich.

I have checked ignition and its all ok. Batt is brand new and it has a high output stator.

What I said above is only with a new plug. After about a day or 2 the bike gets worse. The bike will not start unless the hot start is pulled and it backfires the whole time its trying to start. takes about 10 or 11 revolutions before it will start. Put a new plus in and it will start right away with no back fire but still needs the hot start(even when cold).

Now I have tried to adjust the fuel screw and it has not done anything. with a 45 I can screw it all the way in and it still runs. The idle goes up a little. The 42 does the same thing. I have read a few people say to get a brass screw and that some of the alum ones are no good. Is this true? Some people seem to have better luck with the brass ones.

Valves have been checked and are in inspect.

What is going on with this thing? Is it rich or lean? Why are the plugs acting like they are fouled and making it back fire after a few days of riding? What should I try next.

Edited by Parx_400

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One more thing. When riding slow around town the bike feels like it getting "loaded up" like a 2 stroke would. it seems to effect all performance. once you run it hard its back to the way I have described above. This has always lead me to think it was rich.

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