Engine surging at low throttle cruising

14 replies to this topic
  • MountainMax

Posted May 18, 2006 - 06:38 PM


when im on the road cruising on the road say around 80-90 km/hour and light throttle the engine surges up and down a bit, almost like it's still a bit lean. I have done the free type mods and done the jetting as per the sticky here but it's just not quite right. Also on a decel wnen hearing down i still get a scattered backfire. I also get a backfire if i hit the throttle and rev up the enginge quick and let go of the gas i get one backfire. finally if im at idle and hit the throttle fast she will stall out or bog,bog, bog then rev up. Any ideas, this is not a problem just some fine tuning i think will make it better, so im wondering where to go now, anyone have similar issues on their 06 WR450 ???

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  • ARin

Posted May 19, 2006 - 01:10 AM


surging is caused by the TPS sensor. Unplug it and it will go away, but you will lose a minimal amount of performance.

The sputtering is most likely a "too lean" condition.

rejet accordingly.

  • MountainMax

Posted May 19, 2006 - 07:42 AM


Thanks, i know it's a jetting issue but to what part, maybe move up the needle (drop the clip one slot)??

  • odonnks

Posted May 19, 2006 - 02:12 PM


What throttle position is the surging?? 1/8, 1/4, 1/2, etc..

  • MountainMax

Posted May 19, 2006 - 03:41 PM


it's about 1/8 throttle and worse in top gear around 80/90km/h on the road it feels like it starves for gas then cuts in again,

  • odonnks

Posted May 19, 2006 - 07:13 PM


Try a larger pilot jet or disconnect the tps. The tps is the eaisest to try.
1/8th throttle position isn't enough for the main jet.

  • windaddiction

Posted May 19, 2006 - 07:43 PM


I was told the surging was from no flexable coupling in the rear like most bikes have? is this possible? I only notice it when I ride it on the street

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  • ARin

Posted May 19, 2006 - 09:56 PM


It is the TPS flipping back and forth from two different timing maps.

You can verify that by unplugging the TPS and see if it goes away.

  • odonnks

Posted May 20, 2006 - 02:23 AM


If your referring to the flex coupling in the rear hub on allot of DS bikes its more to protect the drive train from the shock of 50 hp hitting and very little tire spin.

  • MountainMax

Posted May 20, 2006 - 05:56 AM


Well i already have the 48 pilot but still have the stock starter jet, would that matter? the specs here said it should have a 72 stock starter jet and they recommended a 70 so i left it alone, then i found mine only had a 68 (i think or 60 something) starter jet. I have the grey wire mod done and would not like to leave the tps disconnected but i can try it to verify if it's the culperate or not.

  • OneToGo

Posted May 20, 2006 - 06:01 AM


As stated try the TPS first. My guess is it wont entirley cure the surge you feel.
Ride the bike and find where the surge is in the speed range and throttle setting. Pull over and unplug the TPS. Ride the same stretch of road under the same conditions - compare?
The TPS will improve the surge, no doubt. My experience with it was around half the surge was attributable to TPS, the other was ACV induced and related pilot circuit. I found the TPS was needed for smooth running at smaller throttle settings, so mine is reconnnected. The ACV also influences the circuit when there is any change to vacuum. If you still have problems post TPS then do a search for ACV and see what turns up. It had been a much talked about subject earlier in the year.
PS. The bike will improve with age and after all the mods are DONE :ride:

  • Dodjy

Posted May 21, 2006 - 04:35 PM


Mountainmax, Try lowering the needle to lean it off. You are most likely running a bit rich. I had this exact problem and solved it this way without touching the TPS. The TPS is needed to map the ignition (RPM vs TPS).

  • MountainMax

Posted May 21, 2006 - 04:54 PM


I was thinking it may be a lean condition not rich......... thought a rich condition would just make it burn more gas

  • Numskull

Posted May 21, 2006 - 05:42 PM


If you twist the throttle to quick it will bog for a second. Just turn it with more of a smooth rythem, as the acelerator pump is more of a squirt, and quick flicks of the throttle dont work. Even though mine seems very quick, and only notice it on very seldom.

How serious is the surging? Is it just changing rpms, or is it missing and sputtering?

Its probally the pilot circuit

What kind of back fire is it? is it a gun shot or is it more like a crackle? Crackeling is normal but explosions are a sign somthings amiss :ride:

  • Dodjy

Posted May 21, 2006 - 06:52 PM


Yep, I thought it felt lean too, (used to that surging feeling in a car) but rich causes it to do this under light throttle. It probably gets worse when you go higher or it gets hotter? If so, definitely rich.


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