KTM 450 EXC crazy high idle with choke on

[delagem]

Hello,

 

My 2003 KTM 450 EXC 4 stroke has a crazy high idle when the choke is on.  Maybe 4,000 rpm?  Once it's warmed up, and the choke is turned off, the bike idles normally, 1,300 or so rpm.  

 

I can lower the idle while the choke is on, but then, once I turn the choke off, it dies.  Idle needs to be raised up once warm.  

 

This doesn't seem right.  

 

Bike is used as a commuter street bike by my college student son, pretty much only 30-45mph surface streets.  

 

Bike is bone stock, owned since new.  It used to run correctly.  

 

I've been thru the carb once, cleaning jets.  Adjusted the valves once, when it was idling poorly.  

 

Am I missing something here?  

 

Michael

[dudenstumpy]

When I fire up my 2007 525 with the choke out, the bike soon revs much too high for my liking. I therefore reach down and manually hold the choke knob roughly half-way out to keep the revs at the level I want.  Once the bike has warmed, I put the choke full on ( to prevent stalling ), and quickly pull away, then reach down and push the choke off.

[dirteta]

When I bought my 07 the dealer told me as soon as it fires and is running with choke out, push it back in. I can't imagine leaving the choke on for anytime. The bike would rev its ring off.

I may be wrong on this but I would think if the bike is correctly jetted for altitude/temp it should idle fine with the choke off.

[delagem]

Thank you for the replies.

 

But this isn't an issue with how the choke is being used.  Something is mechanically wrong. 

 

I have owned this bike for 12 years.  It used to work correctly, but now, a combination of a much higher idle while the choke is on, combined with the need to run the choke for several minutes before the bike will run properly without the choke, is causing this issue. 

 

So, I need suggestions on two issues.  1. Is there a way to lower the idle when the choke is on, without affecting the idle when it's off?  (Obviously I could do this with the idle adjustment, lowering the idle when I first start it, then raise the idle as I turn the choke off; but raising and lowering the idle each and every time I start the bike cold is obviously not right)

 

Alternately, how do I get the bike to run sooner without the choke?  Raise the float level in the carb?  Air screw adjustment?  The bike didn't used to need 3-4 minutes of choke to warm up; but it does now.  I could live with the high idle for 30 sec or so, or the holding the choke half in for those 30 seconds (in fact that's what I used to do, when it was my bike), but several minutes with the thing just racing away in my driveway rattles my nerves...

 

Obviously rejetting would help, but once again, it used to run right, with the jets that are in it now. 

[Spud786]

Thank you for the replies.

 

But this isn't an issue with how the choke is being used.  Something is mechanically wrong. 

 

I have owned this bike for 12 years.  It used to work correctly, but now, a combination of a much higher idle while the choke is on, combined with the need to run the choke for several minutes before the bike will run properly without the choke, is causing this issue. 

 

So, I need suggestions on two issues.  1. Is there a way to lower the idle when the choke is on, without affecting the idle when it's off?  (Obviously I could do this with the idle adjustment, lowering the idle when I first start it, then raise the idle as I turn the choke off; but raising and lowering the idle each and every time I start the bike cold is obviously not right)

 

Alternately, how do I get the bike to run sooner without the choke?  Raise the float level in the carb?  Air screw adjustment?  The bike didn't used to need 3-4 minutes of choke to warm up; but it does now.  I could live with the high idle for 30 sec or so, or the holding the choke half in for those 30 seconds (in fact that's what I used to do, when it was my bike), but several minutes with the thing just racing away in my driveway rattles my nerves...

 

Obviously rejetting would help, but once again, it used to run right, with the jets that are in it now. 

everything points to cloggage in your slow jet, probably best just to replace it.  That's the jet the fuel screw works with.

[RideFreak]

The choke isn't linked to the idle speed in any way.  What's happening is it's very lean, when the enrichener (you're referring to it as a choke) allows more fuel in the bike is revving up.  That's also why it's taking so long to warm up.  Like Spud mentioned, there's a reduction in fuel in the pilot/fuel screw circuit.  You can run some seafoam and let it sit a week and see if that helps but you really need to pull the carb.  Remove the pilot jet and fuel screw and clean those circuits.  Probably a good idea to pick up a new pilot jet.  They can be difficult to clean properly. 

[delagem]

everything points to cloggage in your slow jet, probably best just to replace it.  That's the jet the fuel screw works with.

 

 

The choke isn't linked to the idle speed in any way.  What's happening is it's very lean, when the enrichener (you're referring to it as a choke) allows more fuel in the bike is revving up.  That's also why it's taking so long to warm up.  Like Spud mentioned, there's a reduction in fuel in the pilot/fuel screw circuit.  You can run some seafoam and let it sit a week and see if that helps but you really need to pull the carb.  Remove the pilot jet and fuel screw and clean those circuits.  Probably a good idea to pick up a new pilot jet.  They can be difficult to clean properly. 

 

 

I don't mean to drag an old thread up from the depths, but just wanted to post what the problem was.  

 

Spud and RideFreak were correct, it was running lean due to clogged jets, and even cleaning the carb jets wasn't good enough.  Replaced the jets, and the bike runs perfect again.  I went with a JD kit, and the choke isn't even needed anymore.  Starts with just a tap of the starter; in less than a minute it'll take throttle gently, within 2 min's it will take throttle aggressively.  

 

Thank you all for the help!

 

Michael

[sirthumpalot]

Thanks for coming back to post the solution, that will help the next guy who has the same problem.  So often people don't post the final solution.  Glad you fixed it! ?

[dirteta]

I don't mean to drag an old thread up from the depths, but just wanted to post what the problem was.  

 

Spud and RideFreak were correct, it was running lean due to clogged jets, and even cleaning the carb jets wasn't good enough.  Replaced the jets, and the bike runs perfect again.  I went with a JD kit, and the choke isn't even needed anymore.  Starts with just a tap of the starter; in less than a minute it'll take throttle gently, within 2 min's it will take throttle aggressively.  

 

Thank you all for the help!

 

Michael

It's great you fixed the problem but there are better jetting combos than the JD kit. If you get the chance to grab one, grab an ocemp or ocemr needle on 5th clip down and about a 160-162 main. You will notice way better throttle response.