07 450 idle flucuations

10 replies to this topic
  • djs383

Posted May 13, 2008 - 05:34 AM


Ok, I'm pretty lost on this one.

07 450 55 hrs on meter. The bike idles just fine in neutral (1950 RPMs). Put it in gear and the idle jumps up to 2500ish. Put it back in neutral and the idle resumes to normal. Oh all this happens without me touching the throttle. Also I just replaced the neutral switch and it still acts up. I can't ride the bike as it is extremely unpredictable in turns and in rythem sections. I figure its electrical but what else can it be now that the switch has been replaced?

  • William1

Posted May 13, 2008 - 06:17 AM


You can unplug the neutral switch and try it. Some prefer it like this.

By design, the ignition mapping is different in gear than it is in neutral. I suspect Yamaha did this to deal with a grabby hot clutch situation.

  • grayracer513

Posted May 13, 2008 - 07:46 AM


They did it to make the bike less likely to kick back on a start. The timing retards in neutral farther than in gear.

Your problem indicates a lean idle. Try this process:


  • djs383

Posted May 13, 2008 - 09:23 AM


I did unplug the switch and the result was the opposite as it had been doing, so for $28 I just replaced the switch. The problem is still there even after the new switch. I know everyone says this, but I went through the carb and put everything back to stock settings it was clean and no problems were visible. It runs fine except that it won't idle down in gear. So with the new switch ruling that out, what next? CDI?

  • grayracer513

Posted May 13, 2008 - 09:52 AM


The function of the neutral switch is to tell the CDI that the motorcycle is in neutral. It does this this by grounding a lead coming from the CDI when the trans is out of gear. The CDI responds by substituting a neutral-only advance map, and by cutting the rev limit.

If the neutral switch is disconnected, the CDI will never leave its normal operating mode, and the idle will stay high.

There are 2 general categories this problem can fall into. One is the point I already made about lean idle. You need to run the test Eddie suggests in the link I posted, check for any air leaks around the carb isolator, ensure that the hot start cable has play, and that the plunger seats. Also, do a check of your valve clearances. Tight intakes can cause this.

The second is that the ignition timing is not being set correctly. This will either be the fault of bad data coming into the CDI, or from a failure of the CDI itself. There are only two inputs; the tach signal, which comes from the trigger coil, and the TPS, which provides load information for mapping the advance. The tach signal obviously exists, because the engine runs. The TPS should be tested thoroughly to be certain that it passes all of the test criteria, and that no sudden spikes or dips in resistance as the sensor is swept from closed to open throttle. If it passes, and the idle mixture has been verified, the CDI may be at fault.

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  • djs383

Posted May 13, 2008 - 10:02 AM


Ok its starting to make more sense. There are no air leaks found anywhere on the intake side. I did take it to a friend that has a shop and he checked valves and adjusted as necessary. He mentioned that my timing was off and he adjusted that......So I will still check the other items, but it seems purely electrical and it may be the TPS, or CDI. Thanks for your help. I've never really had electrical problems before, so I'm new to this headache.

  • grayracer513

Posted May 13, 2008 - 10:23 AM


...He mentioned that my timing was off and he adjusted that......

Explain this, please. The only timing that is adjustable by normal means is the cam timing. If he altered the TPS adjustment (which, by the way, is a pure pain in the butt), he may have caused the problem.

  • djs383

Posted May 13, 2008 - 11:48 AM


He said he did it by cam timing when he did the valves.

  • grayracer513

Posted May 13, 2008 - 12:03 PM


That needs to be investigated to find out why it was off in the first place. If it was caused by a cam seizure, then the intake sprocket may have slipped out of position on the cam.

  • Whyzee429

Posted May 13, 2008 - 06:08 PM


this already sounds like a headache

  • djs383

Posted May 14, 2008 - 10:37 AM


It is, I'm sending it to MX bike heaven....and will get a fresh one. By the time I finish messing with it, it'll probobly be more expensive than dumping it and getting a new one. Thats what I do with my 250F's a new one every year. But, the 08 made it 71 hrs before letting go.

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