can flooding a carb result to oil contamination?

9 replies to this topic
  • yz450fast

Posted May 14, 2009 - 06:12 PM


lubed my throttle cables without shutting gas off. i'm sure there was a flood. bike then resisted starting, then blew smoke for a few. also strange fluid leakage at header. do you think that the gas would've gone into the combustion chamber, and gotten past the piston rings?

  • grayracer513

Posted May 14, 2009 - 07:12 PM


If there was enough gas run past the rings to raise the oil level visibly, the oil should be changed. Less than that will normally evaporate as the engine reaches full operating temperature.

The smoke was probably oily residue lifted off the piston by the gas, and partially burned gas itself.

  • yz450fast

Posted May 14, 2009 - 07:44 PM


no, i diddnt squirt enough in there to raise the level, i just wondering about molecular destruction in my new oil.

  • yz450fast

Posted May 14, 2009 - 07:55 PM


anyone else?

  • Smokeslider

Posted May 14, 2009 - 08:01 PM


most won't answer too much after Grayracer posts because he's the expert here. I'd go with his post.

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  • yz450fast

Posted May 14, 2009 - 08:18 PM


thats cool, much respect. so, minimal fuel would evaporate huh? if th piston was down, and i twisted the gas lets say 20 times, could there be a pollution problem? i guess i just dont want to change my oil again already. i should

  • grayracer513

Posted May 14, 2009 - 08:29 PM


20 times... Seems a bit excessive. Nevertheless, yes, it will dilute the oil, but not very much. Piston position doesn't matter. In order to get to the crankcase, the fuel has to go past the rings, which does not happen quickly.

Gasoline does not dissolve or chemically modify oil, it just dilutes it. It is very unlikely that the amount of fuel involved in 20-30 AP shots would be enough to seriously reduce oil viscosity. If the engine is allowed to reach full temps and stay there for 15 minutes, 99.9% of it will go away.

  • yz450fast

Posted May 14, 2009 - 09:11 PM


thankyou grayracer for your unweilded knowhow, and your uncompremised mechanical knowhow of fourstroke engines:worthy:

  • Wiz636

Posted May 15, 2009 - 07:32 AM


Wait a minute, are we postulating here that 20 ap squirts of fuel somehow got past the intake valves into the cylinder and then sat long enough to seep past the rings?

Wouldn't the leak jet prevent that fom happening?

Even if it did accumulate in the intake area I can't imagine it would all be sucked into the cylinder all at once upon attempting to kick start. Even then, would it be compressed enough to get past the rings with the auto-decompressor?

  • grayracer513

Posted May 15, 2009 - 08:08 AM


Wait a minute, are we postulating here that 20 ap squirts of fuel somehow got past the intake valves into the cylinder and then sat long enough to seep past the rings?

That's what the OP was concerned about. But the volume of fuel discharged by the AP in 20 full shots isn't really enough to do any serious oil dilution even if it went directly to the crankcase.

If the engine was at rest with the intake valves open, the fuel would run directly into the combustion chamber, but only a portion of it would be able to run down past the rings. Some would soak into the carbon on the piston and/or sheet out on the metal surfaces. The fact that it smoked afterward is proof that raw fuel was still present.

Leaving an engine with the gas on and a carb that slowly overflows over a long period can add a significant amount of gas to the oil, but that takes hours to accomplish.

The leak jet would not affect this question. Leak jets don't prevent an AP discharge on a quick twist, only on slower and/or partial twists, and there is no way the leak jet could control where the fuel goes after the discharge.

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