2012 yz450f gas in the oil

11 replies to this topic
  • alh583

Posted November 15, 2014 - 06:19 PM


Ok I know there have been a few posts on this but I never saw any resolution. I have a 2012 yz450f with approximately 35hrs on it. yesterday when changing the oil I noticed a strong gasoline smell and it seemed like I got a lot more oil out of the bike than normal therefore I suspect somehow some fuel got in the oil. I run Rotella triple T and regular 93 gasoline the motor is all stock and has never been apart. Any info would be appreciated to easy my mind about this. Thanks! 

  • alh583

Posted November 17, 2014 - 12:41 PM



  • RockerYZWR

Posted November 17, 2014 - 01:31 PM


Well the only chance fuel would really have to get to the oil would be if it got past the rings. Really worn rings creating a blow-by condition would normally cause a crankcase oil burning problem along with a gas in oil problem, although a tiny bit of gas in the oil over time is normal. But this being a dirtbike, you should be changing the oil often enough to not notice it. 35 hours on the motor should still have plenty of life left on the rings unless you really ride the thing (National Pro) hard.

Otherwise, it could be a faulty injector either not firing at the right time, for too long of a duration, or otherwise allowing excess fuel into the cylinder that drains down past the rings into the crankcase. I don't know what the probability would be of an injector problem in these bikes, though I have heard of car injectors getting stuck open and causing this problem. Fuel pump overpressure is unlikely, but another possible cause.

What does the plug look like? That should be step one because you'd more than likely be running very rich. Other questions to help diagnose - how's it been running, any smoke out the muffler (if so, what color?), and is it hard to start? But pull the plug if you haven't already and maybe post a picture of it here.

  • grayracer513

Posted November 17, 2014 - 02:16 PM


If you cold started the engine and then did not fully warm it up, then keeping it warmed up for a minimum of 10 minutes, your oil will be fuel contaminated.  However, it's also been found that due to the lack of a thermostat, the colder temperatures you currently have can keep the coolant temperature so low that the system never gets out of its warmup mode, which keeps the mixture artificially rich.  You might try covering half of one radiator in the cold to see if that helps the matter.


Another possible cause is a leaking injector nozzle.  If the injector does not close and seal, it will bleed off residual pump pressure into the intake when shut off. 

  • alh583

Posted November 17, 2014 - 04:56 PM


Thanks for the replies!!! Rocker YZWR I definitely think there should be plenty of life left on topend im only a top C low B rider and I have a clam and smooth style of riding without much rev. I haven't pulled the plug yet but will definitely be doing so, but the bike runs great and has never showed any smoke out the pipe. Grayracer513 that's what I have found others suggested on similar posts that the cold weather maybe causing this. It really hasn't got that cold here in the times I've rode the bike it just started getting really cold in the past week and last time I rode was two weeks ago. One consideration I had was I thought about I always pull the fast idle or "choke" to start the bike and let it warm up for 30sec. or so before pushing it in. I only do this when its cold but maybe this doesn't help it running rich when warming up and could be a big contributor. Its a habit from having built carbureted bikes in the past that were very hard to start. I just hope this doesn't turn out to be a big issue. I just got rid of a 2011 crf450 because I had nothing but problems out of it and opted for a Yamaha because I thought they were bullet proof. Thanks!  

  • grayracer513

Posted November 17, 2014 - 05:06 PM


The cold start knob doesn't cause the mixture to be rich during cold starts or any other time.  It's only an additional air path, not an enrichment device.

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  • alh583

Posted November 17, 2014 - 05:12 PM


Ok I wasn't sure just thought maybe that could be a contributor

  • alh583

Posted November 17, 2014 - 06:57 PM


So wouldn't the most likely "problem" be the injector leaking? the bike did sit for a long time before I ran it a few times and then changed the oil. I think the last time I changed it since last Saturday was back in mid September. The bike was apart with the suspension at pro-action had to get a set up im 6'5" and 215lbs so the stock springs and valving weren't cutting it. Therefore it had plenty of time to accumulate some fuel if it was leaking. Plus I broke my femur and dislocated a hip in early May and was out for a long time so when I do ride now I don't have any endurance and am lucky to put in a 12min moto without a break so any fuel in the oil wouldn't really evaporate and the bike never really does get warm because it doesn't run long and I ride it very smooth. Just trying to get a the best opinions you all have to give with all the info I'm a bit OCD and don't want to go through all the problems I did with a Honda with this bike. Thanks again   

  • rah7777777

Posted November 17, 2014 - 07:59 PM


12 minute runs.... That's your problem. Never gets warmed up enough to burn the oil contaminants.

  • RockerYZWR

Posted November 17, 2014 - 10:55 PM


I would change the oil again to make sure you have a known quantity of good oil in there and take it out for a good long easy fully warmed practice session and keep it up at operating temp for at least 30 minutes or so before you go any further in the diagnosis. I'm not there and I don't know much about Yamaha FI, but I sort of doubt it's a faulty injector.

  • alh583

Posted November 27, 2014 - 08:09 PM


Well the plug looked normal I took it out and ran it on the turn track for 3x 30min motos and changed the oil when I cane home. The quantity I put in is what I got out but it had a slight fuel smell but it was not near as strong as before. I did this last Saturday and have left the drain plugs out with a clean pan beneath the bike. My thought was that if it was a leaky injector than it should eventually leak past and drop a drop or two in the pan which it hasnt. I have came to the conclusion that I must have had a leaky injector when it sat for 2 months along with short motos beforehand. Also last Saturday I ran it on basically an overdose of Seafoam so maybe it cleared out. I dont though just my guess.

  • alh583

Posted November 27, 2014 - 08:11 PM


Also the slight fuel smell I got the last time I envision was from left over oil left in the bike from the last oil change


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