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sac 53

yikes...fuel smell in the oil!!!

11 posts in this topic

I took my 2000 426 out on it first ride(it is very fast). When I got home I was checking the dipstick and smell fuel. I changed the oil and ran it with the new oil then drained it again. No smell the second time around. One of the nieghbors said it was because I left the petcock open for a couple of days. I had never heard of that but I am new to riding so he could be right for all I know. Anybody got any ideas what might have caused that or is it normal.

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Just leaving the petcock open will not cause a problem, but if "someone" has a habit of twisting the throttle every time they stop to admire the bike, the AP runs a shot of fuel into the intake, which will find it's way into the oil if the bike is not started soon after.

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Just leaving the petcock open will not cause a problem, but if "someone" has a habit of twisting the throttle every time they stop to admire the bike, the AP runs a shot of fuel into the intake, which will find it's way into the oil if the bike is not started soon after.

I would think that if he smelled gas in his oil, it'd be caused by blow by passed the piston rings. How else would it get in to the oil, can you explain?

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If you place fuel on top of the piston, over time (and it won't take too long) that fuel will run down through the ring gaps and into the oil. Depending on where the engine stops when it is killed, the valves may be held slightly open letting any fuel that is pumped into the intake flow down onto the piston, through the ring gaps, and into the oil. Hope this helps.

Josh

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Even if the valves are closed, the fuel will still leak through.

It's not an o-ring seal... it's a metal-on-metal seal. A good one, but not impervious.

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Wow, that's a lot of what ifs. I think if it's the amount he says, he'd have to deplete the float bowl to saturate the oil enough to smell gas. Do a cylinder leakage test, that will resolve this issue. Thanks for your input, Josh.

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That's not a lot of ifs. It's one "if".... if someone is twisting the throttle and not starting the bike, boom... it'll happen, and you'll probably smell it in the oil until the bike is started and it is boiled off.

This "if" has nothing to do with the petcock, because the bowl contains enough fuel to create the problem.

Now IF the petcock is left open AND if the float valve is stuck, then the bowl could perhaps flood into the intake manifold without anyone playing with the throttle.... but if the bike is running fine and not acting like it's rich, then that's not likely to be the problem.

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A cylinder leak down tester can be purchased from Harbor Freight for about $20-$40 I think. Or you can build your own, Do a search on the INTERNET and you will find several DIY "roll your own" testers. You don't necessarily need the gages, but they would be helpful. Basically you pressurize the cylinder with shop air and listen for a hiss. Air will come out from the exhaust , intake(air box), or the dipstick tube(indicates leaky rings, and some leakage here is normal). This test needs to be done with the engine at TDC unless you pull the cams so that they won't open the valves. That is a quick and dirty description of the leak down test.

Now, since you say there is no fuel smell in the oil now after the oil change I would say run it and forget it. Just pay attention the next couple of oil changes and see if the smell returns. It could have just been a coincidence/anomaly type thing. Hope this helps.

Josh

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A little fuel smell in the oil is normal ''IF'' the oil has'nt been changed in a while.

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