CRF 450 2017 no idle when hot

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6/28/2018 10:09 PM

Hi!

I’ve got a really strange problem with my Honda CRF 450 2017. The bike runs perfect until it gets really hot and that is about 5-6 laps in to a moto. After that the idle disappears completely and as fast as I pull the clutch or don’t have any throttle engagement the bike dies. If I pull to the side and turn the yellow idle screw up about 7-10 klicks the bike idles again and runs as it should but when it cools down and I start it it starts to idle really high whitch is normal in my book because I turned the idle screw up. I have checked the normal stuff like valv clearance and all the connections and everything is good. I think the problem is some electrical or throttle body related.

Hopping somebody has some ideas or had the same problem because I have no idea to what to look for anymore ?

//Philip

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6/29/2018 11:49 AM

Sounds like maybe the idle is set too low when cold.
Could also be an air leak.

Paw Paw

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6/29/2018 1:11 PM

Paw Paw 271 wrote:

Sounds like maybe the idle is set too low when cold.
Could also be an air leak.

Paw Paw

Sorry forgot to say the bike has about 65h on it and up to 2h ago it ran perfectly just the last 2h with problems. The difference between hot and cold is to big to just be a adjustment issue.

I can absolutely check it for leeks just to be safe but I still think it’s something else. If it was leeks I believe the problem would be more consistent not just when it gets hot. You can right me if I’m wrong ?

//Philip

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6/29/2018 2:30 PM

When things break they break. Doesnt matter if it were fine 2 hours ago.

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6/29/2018 2:45 PM
Edited Date/Time: 6/29/2018 2:48 PM

With 65 hours on it, it sounds like it is time to check or replace the top end. Remember that compression increases and decreases when the engine gets warm and that increase or decrease can cause idle issues.

Paw Paw

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6/29/2018 3:10 PM

When was the last time you did any maintenance on the throttle tube/cables?

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6/29/2018 5:56 PM

My 2015 started doing the exact opposite thing. Idles normal when cold but way too high when warm. If you kill it then restart it will idle normally.

The strange thing is that when hot and idling too high, if you turn the idle adjustment knob one click it will lower the idle all the way back down to the normal idle rpm. Probably something with the TPS, but I haven't confirmed that yet.

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11/12/2019 10:08 PM

Paw Paw 271 wrote:

Sounds like maybe the idle is set too low when cold.
Could also be an air leak.

Paw Paw

pb233 wrote:

Sorry forgot to say the bike has about 65h on it and up to 2h ago it ran perfectly just the last 2h with problems. The ...more

2017 honda crf450r catastrophic engine failure. Please e mail me at c6man1@comcast.net with pictures and no bullshit. I am a 30 yr factory master certified automotive tech. Foreman level. Meaning a single cylinder engine compared to what I do everyday is simple. I have built many mx engines and trans. Honda is not owning up to this issue that needs immediate attention before someone looses their life or becomes crippled when the engine shuts down or locks up (as mine did to me) with no other warnings other than aluminum flakes in your engine oil. Up to when I made that customer assistance case, and of course when it took a shit, couldn't be happier with the bike.

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11/24/2019 6:29 AM

I did have kind of same problem, after lots of time searching for the failure it was a bad valve seat in the intake side of the head....valve looked good but the valve seat was a bit destroyed...not that much but if you put some light from Spark plug hole you can see the light if you look from the Throttle body side.

I did check everything before found this problem in the valve seat.

I hope this help.

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10/27/2020 7:04 AM

I have a similar problem with my 17. Kick the motor over it idles for about 2-5 seconds then dies. This will happen 3-5 times before it will stay running, no issues once on the track. That is how the problem started out, went to a race a few weeks ago and it died 3 times in one lap. Bike only has 56 hours on the clock, 30 plus rider so I'm not super hard on the motor or rev limiter. The bike has only ever had T4 in the tank and I have owned it since new. It was programmed not long after I bought it for the fuel and pro circuit exhaust that is installed on it. The only other issue I have had(2 years ago) was the water in the kill switch and that has been replaced since. Tried the stupid things like new spark plug, unplugged the kill switch, drained the tank and tried new fuel, thought the tank could be vapor locked that not the issue. Mapping in the ECU doesn't fail right? Fuel filter, fuel injector, fuel pump? Or do I tell the wife this bike is now unsafe and I go buy a 2021?

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