HELP! yz450f very hard to kick up

7 replies to this topic
  • brent3045

Posted May 13, 2013 - 10:00 AM


bought a yz450f off a friend and for some reason hes cut the sky blue wire and the grey wire on the cdi unit and insulated them apart from the others.
dont know if this i the reason for it being very hard to kick up or not but i have no idea why its so hard to fire by kicking it
will bump easy and runs fine once its started
any ideas appreciated? thanks

Edited by brent3045, May 13, 2013 - 10:12 AM.

  • grayracer513

Posted May 13, 2013 - 10:22 AM


What year model, please?

  • brent3045

Posted May 13, 2013 - 10:37 AM


2004 yz450f

  • grayracer513

Posted May 13, 2013 - 10:53 AM


The sky blue is the lead from the neutral switch. In neutral, this lead is grounded by the switch, but not at any other time. A ground on the sky blue lead tells the CDI that the unit is in neutral, and the CDI responds by making two changes: It lowers the rev limit from 11,500 RPM to 7000, and modifies the timing curve to make the bike start better and help it pass sound checks. This might be a part of your hard starting. To test it, just take a test lead and run the sky blue out of the CDI to any good ground and see if it starts better.

There is no gray wire shown in the schematic of an '03-'05 YZ450. Check the color again.

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  • brent3045

Posted May 13, 2013 - 01:33 PM


just had a quick look at the bike again in the garage and it definitely the grey and sky blue wire. the bike is also 2004, is there any chance this bike is a wrf450? it seems to be too quick to b e a wrf tho
it also has 5 gears

  • woods-rider

Posted May 13, 2013 - 01:42 PM


If it's a 2004 and has 5 gears then it's a WR.

You bought a bike and weren't even sure what it was?

Edited by woods-rider, May 13, 2013 - 01:43 PM.

  • brent3045

Posted May 13, 2013 - 01:48 PM


it doesnt have electric start, wiring for lights, no lights on, 19" rear wheel on, has 48 tooth rear sprocket on, the tank only holds £8, basically everything that a yzf has. the bike is stolen recovered, the engine numbers it shows are of a 2004 bike.

Edited by brent3045, May 13, 2013 - 01:52 PM.

  • grayracer513

Posted May 13, 2013 - 03:48 PM


The WR CDI is easily distinguished from a YZF CDI by the fact that the YZF units have no attached wire harness. The harness connector plugs directly into the box. The WR ignition does have a harness, and there is a gray wire.

On a WR450, cutting the gray wire is supposed to alter the timing map to be similar to the YZ; snappier and more responsive. The wire that is sky blue on the CDI side of the connector in the '03-'05 models connects to a sky blue/white wire on the harness side, and still passes through the neutral switch, but the circuit is different. Some people cut this because it makes the bike start a second or two more quickly under racing conditions.

The '03-'05 YZ450 was a 4 speed. It can be converted by swapping in the entire '03-'06 WR 5 speed, but that doesn't happen very often because it's rather expensive, as you might imagine. Another tell tale is that the WR neutral switch below the front sprocket will have two wires connecting to it rather than one as does the YZF.

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