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jsc1648

Crazy idle

21 posts in this topic

I have a 2004 WR450 and have done the free mods and JD jetting. This has worked fine for me for the past few years and all of a sudden, it wants to idle extremely high. I can put a load on the motor by putting it in first and letting the clutch out a bit and the bike will idle down for a while and then return to a high idle. The air screw and pilot jet and jetting adjustments in general have very little effect on this situation. I switch between sea-level and 9,000+ jetting twice a year and it runs the same way both places. Otherwise, the bike runs fine, but starting is not as easy as it used to be. I've taken the carb off and cleaned it, and the hot-start lever feels functional, but seems to have no effect on the way the bike runs or starts. Thanks for any help.

BTW I searched for this issue and found a couple of posts, but I have a feeling my issue is not simply a jetting issue as it used to run fine as it is now.

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check the hot start circuit.Easy way is to pull in the hot start lever with the motor running and see if the revs raise further.If they don't i would say your hot start is stuck on already.When you pull the lever it leans the circuit and the revs pick up.Cable could be to tight around frame or plunger stuck out in carby or plastic nut on carbi stripped and sucking air,you can get aliminium ones.

Good luck

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Believe it or not, I'm still having this issue. The hot start does not appear to be the culprit. It does affect the idle, although not a bunch. I suspect an air leak, but I can figure out where. Also, it pops a bunch on decel and seems to over heat fairly easily. I have tried running all kinds of jetting options though and still runs this way. I'm at a loss. I don't enjoy riding the bike as the throttle operates more like an on off switch and makes cruising impossible.

Thanks,

Jeff

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Check that the carb is properly seated to the air boot and cylinder head.

Some have suggested spraying starter fluid on the joints to help determine where the leak is.

I had exact same problem-found the leak between carb and head, carb had twisted a little, so not sealing properly. Annoying to ride around with high false idle.

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Thanks for the help, I'll try the starter fluid thing. I've had the carb off probably ten times since this started and it's always the same, so I doubt its a leaky connection between the carb and either boot. I have to admit, I haven't spent the time required to solve this issue. It's very frustrating though. The carb is so much more complicated than two-stroke carbs I don't know all of the ins and outs. It could be something simple, that I just don't know about.

Jeff

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The issue your having is called a hanging idle. Try a search for "hanging idle" you will come up with a ton of stuff.

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If you've ruled out the hot start and are still getting the hanging idle with decel popping and overheating, I'm thinking you've got a plugged pilot circuit. Provided you haven't replaced the pilot jet prior to the problems cropping up, I'd remove the carb, remove all the jets, soak them in carb cleaner, douche out the carb body and blow out the passages with compressed air. If you have a nylon bristle brush of some sort and can pull out one of the bristles, you can use that to ream out the jets without affecting the orifice. Give that a whirl and report back...SC

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Thanks for all the help so far. Although I haven't pulled that carb again as suggested I did determine I was able to make the bike run fairly normal by leaving the choke on and turning the idle way down to a normal idle speed. Does the choke bypass certain circuits within the carb? It seems like perhaps I have narrowed down the issue. I have tried two differnt pilot jets and this didn't change anything.

Thanks,

Jeff

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You've "Hidden" the problem by using the choke, the choke does exactly what it's name implies, it chokes the carbs air supply, thus making your lean condition a little less lean - I really think it's either a plugged pilot circuit, or an air leak (post carb) between carb and cylinder. Listen to Clark4131

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+1 on the pilot circuit.

I believe the pilot circuit terminates in 3 places. The pilot jet, the fuel screw and one of the holes at the bottom of the carb throat. Inspect the fuel screw O ring, spring and washer, make sure they are in the right order, also make sure you don't have the original O ring up in the fuel screw hole. Once clean, not much else can go wrong with the pilot circuit.

Wonder if the TPS can cause these problems? Probably not

Good luck

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Thanks for all the help so far. Although I haven't pulled that carb again as suggested I did determine I was able to make the bike run fairly normal by leaving the choke on and turning the idle way down to a normal idle speed. Does the choke bypass certain circuits within the carb? It seems like perhaps I have narrowed down the issue. I have tried two differnt pilot jets and this didn't change anything.

Thanks,

Jeff

When you pull the choke you are running off the starter jet.

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Not to go against the 'tides of opinion' but... you have a plugged pilot jet. :busted:

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I had the EXACT same issue as JSC posted first. Thanks to Clark for the heads up. Pulled the plug on the bottom of the float bowl and found a layer of what looked like real fine sand. Pulled the jets out and sure enough the pilot was clogged. Reassembeld and all is good now. Hot start lever does it's job like it should. Great bike but hate getting at the carb.

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I had the EXACT same issue as JSC posted first. Thanks to Clark for the heads up. Pulled the plug on the bottom of the float bowl and found a layer of what looked like real fine sand. Pulled the jets out and sure enough the pilot was clogged. Reassembeld and all is good now. Hot start lever does it's job like it should. Great bike but hate getting at the carb.

You think it's hard getting to the carb, try a DRZ-S :applause:

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I had the EXACT same issue as JSC posted first. Thanks to Clark for the heads up. Pulled the plug on the bottom of the float bowl and found a layer of what looked like real fine sand. Pulled the jets out and sure enough the pilot was clogged. Reassembeld and all is good now. Hot start lever does it's job like it should. Great bike but hate getting at the carb.

Just checked out an 08 at the local shop. All looks clean and rowdy as usual but I was looking at the new frame setup and scratched my head when I saw how it inhibited getting at the carb. This looks tuff...:applause: This post confirms my suspicion. But I was reading somewhere that a guy pulls his seat and unbolts the lower subframe mounts so it can rotate upward then chocks it. Dunno what bike he rides but sounds like a must do for these newer models....good luck:mad:

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I had the EXACT same issue as JSC posted first. Thanks to Clark for the heads up. Pulled the plug on the bottom of the float bowl and found a layer of what looked like real fine sand. Pulled the jets out and sure enough the pilot was clogged. Reassembeld and all is good now. Hot start lever does it's job like it should. Great bike but hate getting at the carb.

I had the same "crazy idle" out of the blue and it was the above that fixed my 06.

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Your hot start is stuck open. This happened to a friends bike too. Pull it out of the carb (14mm) and clean/lube real good. If it's really corroded you will need to replace the plunger. Be careful not to over tighten the 14mm plastic bolt, they strip easy. The open hot start plunger allows in extra air to lean out the mixture and the symptoms will sound just like a vacuum leak.

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I took the carb apart Friday and completely cleaned it out and it wouldn't even idle. I took it apart again and let it soak in solvent overnight. In the morning, I sprayed everything out with carb cleaner and compressed air and put it back together and it still has that hanging idle. I was extremely frustrated and decided I would order a new carb on Monday. As I was putting my bike away, a buddy showed up with my bday present, a ZipTy racing fuel screw. I decided to install it knowing it wasn't going to help. I pull the stock one out that I just soaked, cleaned and installed all the way in minus 1 and a quarter turns and put the ZipTy fuel screw in at that exact same position and she started up and ran like she did two years ago. FIXED and I have no idea why.

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