Bike runs rough at 1/8 to 1/4 throttle

12 replies to this topic
  • truckjunky87

Posted August 17, 2009 - 09:02 AM


My bike ('06 450) seems to be missing or stumbling when I'm cruising it at a constant speed. Throttle is between 1/8 and 1/4 open. Pilot jet is a 42, Main is a 155. It does it whether I'm at 4500 or 6000 ft in elevation. The last two rides have been in cooler weather (75 F) and it has seemed a bit worse but it may be that I'm just getting more iritated with it. I've played with fuel mixture screw from 1 to 3 turns out with no help. I've tried the needle clip in the 3rd, 4th and 5th groove without much difference and I've cleaned the air filter without much improvement. Where do I go from here or what have I missed?

  • tachnem

Posted August 17, 2009 - 09:20 AM


What are you riding?

I have the same issue with my '03 450. My needle is still on the 4th clip, 42 pilot, 165 main, just cleaned the entire carb and put in the zipty APS. At steady throttle it really stutters, I'm at just above sea level.

I've searched and found quite a few folks posting the same issue, but have not seen where anyone has resolved it.

  • Anssi

Posted August 17, 2009 - 09:45 AM


The needle jet (what the main jet screws into) or the needle itself can get worn and cause problems as the bike gets more hours.

  • truckjunky87

Posted August 17, 2009 - 09:49 AM


Sorry, I'm on a '06 450.

  • wobblyknobby

Posted August 17, 2009 - 09:51 AM


Sounds like the TPS is malfunctioning or needs adjusted.

  • Kasjok

Posted August 17, 2009 - 10:28 AM


I had the same problem and cured it with rising the needle on position.

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  • LumpyBoy

Posted August 19, 2009 - 02:57 AM


Try disconnecting the TPS and riding it.

  • nwbikerider

Posted August 19, 2009 - 08:56 PM


+1 on disconnecting the TPS. My '09 stuttered at steady throttle. I was bull headed and tried to jet it out with no luck. Finally unhooked it and it smoothed right out. I should have learned after i did it to my 426.

  • truckjunky87

Posted August 20, 2009 - 04:59 AM


Sounds too easy but I'm willing to give it a try. What are you giving up by disconnecting the TPS?

  • grayracer513

Posted August 20, 2009 - 08:37 AM


Sounds too easy but I'm willing to give it a try. What are you giving up by disconnecting the TPS?

You'll be giving up the "3-D" ignition advance mapping (timing is controlled based on engine speed AND load condition) and defaulting to mapping based solely on engine RPM. When it works as it should, fuel economy and engine cooling are improved by using 3-D mapping, along with the overall crispness of the engine. If it doesn't work right, the major diameter of the needle may need to be changed, or the TPS may be faulty or maladjusted.

  • truckjunky87

Posted August 24, 2009 - 07:38 AM


Well, I moved the clip to the 3rd groove, cleaned the air filter again and drained the gas from the tank and replaced it and it is now running better at 1/4 throttle cruising, not perfectly smooth yet but better. The TPS is still hooked up but I'm going to keep fiddling with it before I unhook it.

  • Anssi

Posted August 24, 2009 - 08:11 AM


It takes like 10 seconds to disconnect the TPS (the connector in the wires) and it will not damage the bike. Why not just give it a try?

  • grayracer513

Posted August 24, 2009 - 08:18 AM


Why not just give it a try?

Why cover up the real problem by disabling it? If the TPS is OK, and the jetting is off, there's a good chance you'd be doing exactly that.

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