yz450 big bore over heating

25 replies to this topic
  • CRFsandspitter

Posted March 01, 2015 - 09:44 PM


I have a 2006 yz450 with the Athena big bore kit in it. Just got it. It's a little hard to start and dosent idle. When you are on the throttle it's fine when you let off it pops and snaps. Also the header will glow orange. I know this is because it's to lean. What are your guys suggestions.

  • LoonRider

Posted March 01, 2015 - 10:08 PM


Well if you know it's too lean beef up the jets a little...

  • x_JT_x

Posted March 01, 2015 - 10:13 PM


It's lean, you know it's lean, fix it. Why would you need suggestions?

  • WilfulLemar20

Posted March 02, 2015 - 12:18 AM


I have the same problem with my 04 yz450f not sure what's done to it only know it still has stock cams mine ideals now but when it revs it will bang and pop and shoot flames and sparks and seems to heat up rather quick I am new to this engine design all help is apriciated thanks

  • NitrousR1

Posted March 02, 2015 - 03:36 AM


The Lean Jetting is not helping the overheating. I have a 06 with the Athena kit and hotcams. The coolant jackets are 30 percent bigger on the athena cylinder.
I put a boysen water pump impeller and cover on mine and it will idle for 5 minutes on a 100 degree day without overheating. Definitely worth the money

  • WilfulLemar20

Posted March 02, 2015 - 03:37 AM


Good to hear my bike had a boysen water pump already installed

  • Slow and Jerky

Posted March 02, 2015 - 04:47 AM


Clean the  carb, you probably have a dirty jet.

  • grayracer513

Posted March 02, 2015 - 07:40 AM


Any correctly jetted, healthy YZ450F will backfire on deceleration.  It shouldn't be constant, and it shouldn't do it all the time, every time, just some crackling and popping.  The header will also normally glow a dull red visible in reduced light like twilight, dark shade, or the interior of the average garage at night.  None of that means it's lean, and richening the carb to "fix it" will make the bike run dirty.

  • CRFsandspitter

Posted March 02, 2015 - 06:59 PM


Cleaned the carb wasn't dirty no jets were pluged it has a size 55 pilot jet I'm pretty sure stock is a 45. I rode it the other day only about 200 yards and the pipe was glowing almost all the way up to the heat shield on the header. I also pulled the spark plug and that looked fine didn't look like it was running lean or rich. So the main problem is now that the header is just glowing. It was kinda dark the other day but it looked brighter then a red it was almost orange.

  • LoonRider

Posted March 02, 2015 - 08:28 PM


Is it possible your idle is just high? I understand that the header is supposed to glow but if it's glowing as much as you say, and with the jetting specs you provided I wouldn't say it's running lean. Did you let it idle for too long?

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  • CRFsandspitter

Posted March 03, 2015 - 07:17 AM


No didn't let it idle at all. Fired it up with the choke. Then turned the choke off and took off down a field 100 yards down 100 yards back and the pipe was glowin. Should I just try like a 58 pilot or 60?
Also my elevation is only like 100 or 200 feet.

  • LoonRider

Posted March 03, 2015 - 08:48 AM


Yeah that already seems a little rich.
Are your fluids topped off? Mainly your radiator fluid, not sure if that could cause your pipe to glow or not.
Is it stock pipe or aftermarket?

  • CRFsandspitter

Posted March 03, 2015 - 10:35 AM


Stock pipe. I was told it has stage two hot cams as well

  • WilfulLemar20

Posted March 03, 2015 - 03:29 PM


Best bet would be to take your plug out and see what color it is brown,white,or black better they adjusting it to lean and cooking your engine

  • x_JT_x

Posted March 03, 2015 - 06:09 PM


Don't go off the previous post. You have to do a correct plug chop to get a good reading. Just pulling the plug now won't tell you anything.

  • WilfulLemar20

Posted March 03, 2015 - 06:10 PM


What is a correct plug chop?

  • CRFsandspitter

Posted March 03, 2015 - 06:24 PM


Just went and talked to the local shop guy and he was also surprised at how rich the pilot jet was but he pulled the fuel mixture screw out and notice the washer was on the opposite side and that the spring didn't look right for it either. He held up another yz450 screw and sure as she the spring was much different looked more like a spring out of a retractable pen. He suggested that I replace it so that's what I'm going to try next. Also going to get a smaller pilot jet.

  • x_JT_x

Posted March 03, 2015 - 06:26 PM


What is a correct plug chop?

Wide open throttle, with a brand new plug, and you hit the kill switch and don't let it fire at all.

  • WilfulLemar20

Posted March 03, 2015 - 06:28 PM


Never heard of such a thing but nothing is built like it use to be thanks for the information

  • CRFsandspitter

Posted March 03, 2015 - 08:34 PM


Wide open throttle, with a brand new plug, and you hit the kill switch and don't let it fire at all.

He is right. Guy at the shop told me the exact same thing

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