2009 YZ450 Bogging

7 replies to this topic
  • iluvcrowds

Posted March 01, 2011 - 04:59 PM


I apologize in advance for my ignorance on this one, I'll try not to bore you with details and get to the point....

I currently have a 2009 YZ450 that I purchased as a leftover earlier this year to replace the 2008 YZ450 that I previously owned. The bike is pretty much stock and has approximately 30hrs on it (no aftermarket pipe, etc). I typically race a few harescrambles throughout the year and use the bike primarily for woods riding in SE North Carolina. I entered my first enduro this past weekend at the Sandlapper in South Carolina and had some issues with the bike bogging to a stall in corners after getting fairly hot through the tight stuff. During the third leg of the race (approx 25 miles from start) the engine completely died and I couldn't restart. I checked the gas and it appeared as though it was empty. The outside temperature was slightly over 80 degrees and the terrain was considerably tight compared to the typical harescrambles/GNCC's that I have raced in the past. After re-filling the gas, the bike started without hesitation and ran normally, so I decided to continue riding to see the rest of the course. Approximately 20mins after re-starting, the engine began displaying the same problem with bogging to a stall and was hot again.

My questions are....
1) I can't believe that I would have gone through all of my gas only 25 miles into the race. Could I have burned that much? Did I boil the gas out of vent from bike being hot?

2) Maybe the tank wasn't completely empty and bike was just overheated? I checked the gas but was pretty much in a state of delirium when doing so!

3) Could gas consumption and/or bogging be due to the engine running rich?

4) Solutions? I remember my 08 doing the exact same thing on a few occasions if it got really hot in very tight singletrack but never to the extent of this one. I think the difference with the 08 was that when it happened, the tight sections were followed by some open stuff that would effectively cool the bike back down. If it is simply an overheating issue (had coolant in bike)...Bigger radiators, engine ice, etc?

Any suggestions would be greatly appreciated. Thanks.

  • yz450fcranker

Posted March 02, 2011 - 09:42 AM


record engine temperature during the whole race and put just enough fuel for the race if it didnt make it then there must be somthing with overheating fuel consumption

  • rcdude33

Posted March 02, 2011 - 09:51 AM


I know that 08 had a bog when I rode and the motor is the same as the 09 and it would bog a little as well. I think it maybe your jetting because these bikes come lean from the factory, because of emissions.

  • dvn

Posted March 02, 2011 - 10:33 AM


I think it maybe your jetting because these bikes come lean from the factory, because of emissions.

The 09 is not jetted lean from the factory and there are no emissions regulations on MX bikes. These bikes need lots of air flowing through the radiators. I've never had a problem but I only ride moto. Hopefully some off-road guys will chime in with suggestions on the overheating issue.

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  • grayracer513

Posted March 02, 2011 - 12:13 PM


Yes, the bike can be misbehaving because it's too rich. Look up the base '09 jetting in your manual, or in the jetting sticky and compare that to what you are running.

On the heating issue, one thing you did not mention was whether you were losing coolant because of it, or if coolant loss was contributing it the heating.

  • iluvcrowds

Posted March 07, 2011 - 05:01 PM


Thanks for the input. Grayracer...I didn't loose any coolant. Never "boiled over" and the coolant level was pretty close to the pre-race level when I looked at it a few days later. Never changed the jetting on my 08 and it would bog sporadically when hot. When I say sporadically, I mean maybe 5 times out of the year that I owned and raced it. I rode Wednesday and Saturday after draining the gas tank/carburetor and putting a very lightly oiled air filter on; and bogging was almost unnoticeable but was riding on a much faster, open course. Air temp wasn't quit as high either. Correct me if I'm wrong, but I just have in my head that it's too rich not lean. Do the symptoms that I've described support this thinking? Do you think turning the fuel screw in a quarter of a turn would help?

  • grayracer513

Posted March 08, 2011 - 07:44 AM


It could be too rich. High temperatures call for leaner jetting, though usually, the bike will tolerate a very wide range. Still, if it's a little bit on the rich side and the altitude is up a ways, the hot day could be all it takes to go over the line.

  • iluvcrowds

Posted March 09, 2011 - 04:28 PM


Thanks again Grayracer. I'm sure you've heard it a thousand times, but you are a tremendous asset to the forum.

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