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High Idle When Hot

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My DRZ has had a high idle when hot for a little while now. It only idles high when I am coming to a stop and pull the clutch in. If I let the clutch out quickly then bring it back in right before I stop, it will stop idling high and return to normal idle, sort of like I'm loading the engine when I do that.

 

It also did it before I put my JD Jet Kit on, but now it seems to be getting worse with kit on. I installed the 160 main and 25 pilot using the blue colored pin on the 3rd position.

 

The bike runs flawlessly except for this and moderate popping on the decel. Starts up fine, idles fine when cold, don't have any problems there.

 

Any help is appreciated. Thanks.

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I'm having the same problem as well as some other dude, who posted a few days ago. None of the solutions seem to really address the issue. Or at least I fail to see how a dirty Carb would increase fuel flow, which is the only thing that would cause a higher than nominal idle. Right? So cleaning the jets, needles, ports etc, would reduce fuel flow. If anything, in my mind, it would increase fuel flow. Someone help me understand the reasoning behind how cleaning the carburetor to reduce the idle speed.

I appreciate it guys and gals.

Edit: Also, pizza, isn't it a situation of running too rich?

Edited by deadpieface

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High idle is a lean condition, check for air leaks at the intake boot between the carb and cyl. head .

Propane torch unlit will show if there is a vacuum leak.

Edited by Kioti

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I'm having the same problem as well as some other dude, who posted a few days ago. None of the solutions seem to really address the issue. Or at least I fail to see how a dirty Carb would increase fuel flow, which is the only thing that would cause a higher than nominal idle. Right? So cleaning the jets, needles, ports etc, would reduce fuel flow. If anything, in my mind, it would increase fuel flow. Someone help me understand the reasoning behind how cleaning the carburetor to reduce the idle speed.

I appreciate it guys and gals.

Edit: Also, pizza, isn't it a situation of running too rich?

 

Nope. As you lean out an engine it goes up in RPM.

 

As cooler weather approaches the air gets thicker and our bikes get more lean. Turn your fuel screw out an excessive amount. Set your bike to idle a little faster then usual. As you turn your fuel screw back in you will hear the rpm go higher and higher until it starts to suddenly drop off. Go back to the high point and then give it an extra quarter or half turn to rich. Once you have your mixture set correctly you can readjust your idle to whatever you like.

 

Another quick test out on the trail is when sitting at idle rev your bike through the lower rpms as quickly as you can (blip the throttle with as rapid a motion as possible, I use a rolling motion between my thumb and index finger). If your engine stumbles through the lower rpms then you are too lean.

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Lean symptoms can look and sound the same as too rich symptoms

Edited by mickeydee

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+1 to mickydee

Went and turned the mixture screw out (richer) and the high idle was worse. So then I turned it in all the way, then back out only 2 turns (it idled high at 2 1/2 turns out). The high idle is gone. Idles normal now.

Unfortunately this did have a drawback. It backfires a little more on the decel due to it being leaner This may require a higher than 25 pilot. We'll see.

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High idle is a lean condition, check for air leaks at the intake boot between the carb and cyl. head .

Propane torch unlit will show if there is a vacuum leak.

 

Thanks for the tip.  

 

Nope. As you lean out an engine it goes up in RPM.

 

As cooler weather approaches the air gets thicker and our bikes get more lean. Turn your fuel screw out an excessive amount. Set your bike to idle a little faster then usual. As you turn your fuel screw back in you will hear the rpm go higher and higher until it starts to suddenly drop off. Go back to the high point and then give it an extra quarter or half turn to rich. Once you have your mixture set correctly you can readjust your idle to whatever you like.

 

Another quick test out on the trail is when sitting at idle rev your bike through the lower rpms as quickly as you can (blip the throttle with as rapid a motion as possible, I use a rolling motion between my thumb and index finger). If your engine stumbles through the lower rpms then you are too lean.

 

Yeah, you do have a point of dense air.  But the increase in RPM is a couple grand.  And it only occurs after it the engine warms up and I can slow it by popping clutch briefly.  You seen that before?  Seems a little high but I am not ruling it out.

I bought it from a dealer with 792 miles on it.  The previous owner may have messed with carberatur.  I a, going to yank it out when I get a free day here Tuesday.  I will play around with the fuel and idle before breaking it open just to try and isolate the actual cause and report back.

 

Lean symptoms can look and sound the same as too rich symptoms

 

Yeah, adds a couple extra steps in troubleshooting.  I haven't had a chance to get her open yet.  Only reason I am asking so many questions.  Just feeling out the experienced folks before I start tearing her down a bit.

 

+1 to mickydee

Went and turned the mixture screw out (richer) and the high idle was worse. So then I turned it in all the way, then back out only 2 turns (it idled high at 2 1/2 turns out). The high idle is gone. Idles normal now.

Unfortunately this did have a drawback. It backfires a little more on the decel due to it being leaner This may require a higher than 25 pilot. We'll see.

 

What happens when you start it cold now and bump the clutch?  Does it come closer to stalling, where as before it would slow the engine?

 

 

Thanks everyone for the polite help.  I really appreciate it.  You never can tell how it will be on a new forum.

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Thanks for the tip.

Yeah, you do have a point of dense air. But the increase in RPM is a couple grand. And it only occurs after it the engine warms up and I can slow it by popping clutch briefly. You seen that before? Seems a little high but I am not ruling it out.

I bought it from a dealer with 792 miles on it. The previous owner may have messed with carberatur. I a, going to yank it out when I get a free day here Tuesday. I will play around with the fuel and idle before breaking it open just to try and isolate the actual cause and report back.

Yeah, adds a couple extra steps in troubleshooting. I haven't had a chance to get her open yet. Only reason I am asking so many questions. Just feeling out the experienced folks before I start tearing her down a bit.

What happens when you start it cold now and bump the clutch? Does it come closer to stalling, where as before it would slow the engine?

Thanks everyone for the polite help. I really appreciate it. You never can tell how it will be on a new forum.

I will let you know tomorrow. Haven't started it cold yet. But definitely mess with the mixture screw first before pulling the carb apart.

If you mixture screw hole has been drilled out, then the carb has definitely been messed with. If its not drilled out, you will need loosen the clamps on the carb and angle the carb outwards more, the drill the hole out.

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My DRZ has had a high idle when hot for a little while now. It only idles high when I am coming to a stop and pull the clutch in. If I let the clutch out quickly then bring it back in right before I stop, it will stop idling high and return to normal idle, sort of like I'm loading the engine when I do that.

 

It also did it before I put my JD Jet Kit on, but now it seems to be getting worse with kit on. I installed the 160 main and 25 pilot using the blue colored pin on the 3rd position.

 

The bike runs flawlessly except for this and moderate popping on the decel. Starts up fine, idles fine when cold, don't have any problems there.

 

Any help is appreciated. Thanks.

 

do what mickeydee suggested....are you using an extended fuel screw? do you need choke when cold?

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No I do not have the extended fuel screw, nor do I need choke when cold.

I took a test ride this morning, it was about 60 F out, started right up. Still runs good and idles normal, but I have to admit, it felt better with the screw richer.

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