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Discussion Starter · #1 ·
I changed my petcock this weekend because it had a small leak. Its gravity fed "on/off/reservere". It seems fine now no leak after taking it for a run. Runs great no issues.

I parked it for a few days and left the petcock "on" position. I noticed today that the oil level had gone up since I last checked and decided to drain the oil. Sure enough the oil had gas in it.....Is this normal for these gravity fed petcocks to leak gas into the oil if you leave them on the "on" position? Or is this a sign my carb float is stuck?

I plan to drain all the oil and let it sit over the weekend so all the gas can evaporate out the system. Do I need to replace the oil filter as well? Is there anything else I can do to avoid damaging the motor after adding new oil?
 

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The non vacuum style fuel petcock On/Off/Res are gravity fed. Meaning fuel flows regardless of if the engine is running or not. So it is not a float issue with your carb. So it is imperative that you flip the valve on the fuel petcock from the On position to the “Off” position whenever the engine isn’t running. The next I’d be concerned about is the gas in your oil. You’ll have to drain that oil and fill it back up. Then drive it around for about 10 - 20 kilometres then change it again. On the final one make sure you replace the oil filter with a new one.
 

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Discussion Starter · #3 ·
The non vacuum style fuel petcock On/Off/Res are gravity fed. Meaning fuel flows regardless of if the engine is running or not. So it is not a float issue with your carb. So it is imperative that you flip the valve on the fuel petcock from the On position to the “Off” position whenever the engine isn’t running. The next I’d be concerned about is the gas in your oil. You’ll have to drain that oil and fill it back up. Then drive it around for about 10 - 20 kilometres then change it again. On the final one make sure you replace the oil filter with a new one.
Do you think changing it twice is necessary? I drained the oil last night and left the cap and plug off to help the gas evaporate overnight.

I am planning to flush some new oil through with the drain plug off a few times before completely filling with oil. The bike hasn't been run with the gas in the oil, I noticed it just before starting it up for a ride and drained it right away
 

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Discussion Starter · #4 ·
The non vacuum style fuel petcock On/Off/Res are gravity fed. Meaning fuel flows regardless of if the engine is running or not. So it is not a float issue with your carb. So it is imperative that you flip the valve on the fuel petcock from the On position to the “Off” position whenever the engine isn’t running. The next I’d be concerned about is the gas in your oil. You’ll have to drain that oil and fill it back up. Then drive it around for about 10 - 20 kilometres then change it again. On the final one make sure you replace the oil filter with a new one.
Thks for your help. Do you think leaving the petcock on is the cause for the gas in the oil or do I have something else to be concerned about?
 

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The fuel petcock is most likely the cause of the gas in your oil. That’s why I said the On/Off/Res fuel petcocks are gravity fed. Meaning fuel flows regardlessly in either position, (On/Off/Res). Change your oil a couple times then take it out for a couple spins. After each ride ride make sure to put the fuel petcock on the “Off” position. Before each ride check the oil level to make sure it hasn’t risen. If the level stays the same then you know the issue was your fuel petcock.
 

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I disagree. Fuel in your oil has nothing to do with the petcock being left on. It would just leak out of the carb bowl drain, not into the engine crankcase.
Fuel in the oil is generally caused by a rich mixture or bad rings. Black smoke is too rich a setting in the carb and white smoke is worn out rings.
 

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I sorta disagree seeing if you leave a vacuum style fuel petcock in the Pri (Prime) position with the engine off it does exactly that. Prime works exactly in the same manner as “On” on a non vacuum style fuel petcock. Both those settings on both fuel petcocks are gravity fed and can and will contaminate your oil if left in a free flowing state with the engine off. I seen this way to many times over the years.
 

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I disagree. Fuel in your oil has nothing to do with the petcock being left on. It would just leak out of the carb bowl drain, not into the engine crankcase.
Fuel in the oil is generally caused by a rich mixture or bad rings. Black smoke is too rich a setting in the carb and white smoke is worn out rings.
A bad petcock can ABSOLUTELY cause fuel to enter the engine. The needle seat may also be compromised, leaving the petcock as the only device in place to control the flow of fuel.

Years ago, cautions were published in some owners manuals warning owners not to leave the petcock in the “Prime” position to avoid fuel contamination into the engine.

Yes, gas in engine oil can be cause by bad rings, a stuck needle seat , overly rich jetting...

There have been many documented cases of petcocks causing mysteriously high oil levels and contaminated fuel.
 
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