2010 yz450f won't idle without high *FIGURED OUT*

Silverfox71
Edited Date/Time 4/18/2021 6:03am
I have purchased this bike recently. Most recently the bike had been running well during a outing. The bike was brought home. The next time out the bike wouldn't start. The bike was brought in and the complete fuel pump assembly was replaced and a clutch cable. The bike was serviced at the same time. Brought it home and started the bike. The bike ran until warm then shit off the high idle button. The bike dies immediately! I pull the high idle and the bike takes a kick maybe 2 and starts right up. If I leave the high idle pulled the bike continues to run. If I twist the throttle fast it dies immediately. If I do the same rest again but twist the throttle slowly just a little I can then crack it open and it has no hesitation what so ever! I tested the throttle position sensor and adjusted it slightly. This has not made any difference in the way it runs. Any suggestions as to what to test next without just blindly ordering parts?

Thanks,
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kb228
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kb228 4/16/2021 4:25am
4/16/2021 4:25am
Reset the idle speed and check the throttle cable adjustment. You might need to look at your sensors that dictate fuel mixture because one of them may be bad
Silverfox71 4/16/2021 4:29am
4/16/2021 4:29am Edited Date/Time 4/16/2021 4:31am
Sounds good KB228 I will give that a shot and let you know if there is anything that comes from testing. I did check the free play on the throttle and that part looks good but have not checked the adjuster on the throttle body. I will compare that to the manual as well. I can tell you that at rest the butterfly is closed completely.
Silverfox71 4/16/2021 7:59am
4/16/2021 7:59am
Is there any way to test some of the sensors with an ohm meter on the bike related to fuel or temp sensors without the code reader? I have already looked at the TPS and it all looks good.
charlie68
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charlie68 4/16/2021 9:43am
4/16/2021 9:43am
Sounds to me like your idle is set too low, give the cold start knob 2-3 clicks counterclockwise and see if that helps..

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Paw Paw 271
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Paw Paw 271 4/16/2021 10:23am
4/16/2021 10:23am
charlie68 wrote:
Sounds to me like your idle is set too low, give the cold start knob 2-3 clicks counterclockwise and see if that helps..
X2

Paw Paw
Silverfox71 4/16/2021 11:29am
4/16/2021 11:29am
Is there a way to check the rpm without special tools? Maybe with an ohm meter?
I will try some adjustments and let you all know how it turns out.
Day30
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Day30 4/16/2021 12:58pm
4/16/2021 12:58pm
Hour meter/tachometer is what you’ll want to check idle rpm ($15 probably at any motorcycle retailer). Look at your manual to see what idle rpm should be. My Honda 450 says it should run a 2000rpm idle and that’s like revved to the moon starting gate idle. I have it at 1100 which gives me the right engine braking I want. it does indeed sound like this easy fix is what will work. You don’t necessarily need the tachometer to test if this is the solution just turn your idle high and see if it works. You can get it pretty dang high with no issues as the manual probably says to do so, then tune it back down how you feel comfortable with it running and to keep it running.
Silverfox71 4/16/2021 5:38pm
4/16/2021 5:38pm
Okay so I tried the fast idle setting. I can't seem to keep it running unless I stay on the throttle at least 1/16-1/8 of a turn...rally it's just enough to keep the butterfly open just a little. I had also pulled the air cleaner just to ensure it wasn't causing an issue. I start the bike and it runs nice and just dies off after a few seconds if I'm not on the throttle. It happens quite quickly almost as if I hit the kill switch. It a had scratcher for sure! What's the next thing to try?
Silverfox71 4/16/2021 5:45pm
4/16/2021 5:45pm
Even with the high idle pulled I'm needing to keep the throttle up a was to keep it running. It stalls an a kick maybe 2 and it runs. If I don't touch the throttle couple seconds and off!
Silverfox71 4/16/2021 6:57pm
4/16/2021 6:57pm
I thought I would add that when I purchased this bike the owner through in a power commander V which he said had never been used. When I went through the box and looked at the connectors I beleive what he said. This thing has never been out of the box and for sure not hookedbuo to anything!
Silverfox71 4/16/2021 7:14pm
4/16/2021 7:14pm
More testing on the white wires from the stator which are giving me a reading around 1.0-1.1 but my shop is also about 15 degrees instead of the recommended 20 degrees. Not sure if this is a potential problem? I'd hate to shell out this kind of money to find it isn't the problem!
Silverfox71 4/16/2021 7:16pm
4/16/2021 7:16pm
The other day when I brought the bike home it was just below freezing and when I got it running it definitely ran much much longer. Now when in the shop it's only a few seconds unless I keep on the throttle no matter what I do
Silverfox71 4/17/2021 2:27pm
4/17/2021 2:27pm Edited Date/Time 4/17/2021 2:31pm
I did some more testing today. I drained all the oil and refilled. It looked like it was somewhat overfilled. I checked my stator and it will only go as low as 1.0 ohms. My shop temp would have been around 15- 18 degrees. The book says .90 - .60 and 20 degrees temp. I found someone who has a used one taken from a seized bike but he says his ohms put at 1.5 ohms. He did say that his garage was only 8 degrees though. Not sure what to think. One thing is for sure that it will idle longer if it's cold. Any more suggestions? I am looking at buying a complete set of electronics for this bike but hate to waist the money!
Silverfox71 4/17/2021 2:50pm
4/17/2021 2:50pm
I will add that with the idle turned up it sounds like it skips or miss fires every few cycles. This maybe why its stalling? If it was electrical wouldn't it make sense that you wouldn't be able to keep it running when even if you keep on the throttle? And if it's not electrical, what mechanical would affect running when it gets cold or warm?
Silverfox71 4/18/2021 6:25am
4/18/2021 6:25am
Thanks to everyone for the ideas that they shared both in relation to my issue here and others experiencing similar problems! The most Valuable lesson I learned through reading from this site and others relating to 4 stroke motocross bikes is.......READ YOUR MANUAL BEFORE YOU START WITH YOUR BIKE! When you bring one of these 4t bikes home.....unless it's new, do a complete service and follow all the instructions to a T!
It seems that the previous owner had this bike serviced at the same time the fuel pump assembly was replaced! This is only a guess, but I believe only 1 drain plug was pulled and the full 1.2 liters or more was added! I dropped what looked like almost 1.5 times as much as the recommended amount. I read on another post of this happening to someone else. I had started it a few times and still didn't seem to be working! The post I read also said it took him to run a tank of fuel through before it started running the way it should. Later I had a friend stop by so I was going through the motions to show him what it was doing. After I had it warm I showed him how it sounded if I tried to crack the throttle and how it wanted to stall but if I slowly opened the throttle I could crack it all I wanted and it would work fine! After doing this I got off the bike and let it idle. To my surprise It stayed running and sounded amazing! I let the bike just idle there for 10 or 15 minutes no problem, even if I cracked the throttle from the relaxed state no problem! I am ecstatic! Was it the oil or was it something else? I don't know for sure but I can tell you it is running very well and very different than it has up till now! Thanks again for the help provided! Keep the rubber to the ground and we'll see you out on the trails!
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