gas in the airbox

[roadrunner]

hey all.. so i decided to maintain while i wait for tires and yesterday got to buisness. pulled the tank for easy access to the plugs which were 15k past due, no problems all even... serviced the battery, thank god because in all there was probably one cell worth of fluid. filled. i decided to dig into the parts bin and do the air cleaner element and in doing so found out that there is a bit of varnished gas in the air box area.. now, the thing was so dang dirty and im wondering if that has anything to do with it??? (the dirty element and the gas) any thoughts??? i pulled the breather resevior thats right under the thing and cleaned all ends and no clogs or crap in there. its for sure backing gas out of the carbs. why else would it do this?? :confused:
meanwhile.. my tires are here and today i attempt to do them myself for serious this time...

[Rex Raider]

a really clogged air filter will make the bike run rich (pulling more gas into the the carbs) and the over flow gets to the airbox. clean the filter and check it again after your next ride to see if still pulling gas to the airbox.

[roadrunner]

thanks steve..!!!

[kneedragger26]

I am going to get technical but you may not like the answer.

1. Here is what happens. Your valves open and close on a four stroke motor. This happens at a very fast revolution. anywhere from 800 up to 15,000 revolutions per minute.
2. Now what happens with all cyclinders is valve overlap. That is when the exhaust valve is closing and the intake is starting to open. The intake lobe and the exhaust lobe are very close and the reason for this overlap is to cool the exhaust valve a little before it seats, using the intake air as the coolant. Now this happens in a 100th of a second.
3. With that understood, you also have a valve lash on the exhaust and the intake valves.
That clearance that I am talking about is always less in intake valves, so.......
4. When the valve clearance at the intake valves disappear,(WHICH ALWAYS HAPPENS ON OVERHEAD CAM ENGINES), then the intake opens prematurely pushing gasoline which is mixed with hot air backwards into the airbox.

So to put it in laymans terms, without knowing anything about your motorcycle such as mileage maintenance, etc, I am willing to bet that you need the valves adjusted.

[rickster]

Another possible cause for the stuff in the airbox is that the crankcase is usually vented to the airbox, so that any air that might enter the crankcase is clean (filtered). The flip side of this is that the natural blow-by gases, created by combustion pressure leakage past the rings, are directed up into the airbox via the crankcase vent hose. This creates a film of oil inside the airbox when the oil vapor condenses. Since you could acually see the stuff, I'd be inclined to think it's from blow-by, as fuel evaporates so fast it wouldn't likely still be in there by the time you got the airbox open. It will smell like fuel, though. In any case, unless you see a big accumulation of oil in the airbox or your engine consumes a lot of oil (more than a quart between changes, depending on how hard you thrash it) I wouldn't worry about it. Just wipe it out, put it back together, and ride it. :blah-blah

[roadrunner]

I am willing to bet that you need the valves adjusted.
even with the hydraulic(sp?) valves that are on the bike???

[roadrunner]

nice. i wondered about that too. i drain the breather pretty regularly and ive been noticing that the resevior from the crank breather/vent deal, which is right directly beneath the air box has been a bit mucky. i pulled and cleaned it and no problems.. maybe i need to drain more frequently. i certianly fills faster during rain riding season. fortunately the drain hose is clear so i can see right away when its got stuff in it. ... 59k and have never had an oil use problem.. :)



Another possible cause for the stuff in the airbox is that the crankcase is usually vented to the airbox, so that any air that might enter the crankcase is clean (filtered). The flip side of this is that the natural blow-by gases, created by combustion pressure leakage past the rings, are directed up into the airbox via the crankcase vent hose. This creates a film of oil inside the airbox when the oil vapor condenses. Since you could acually see the stuff, I'd be inclined to think it's from blow-by, as fuel evaporates so fast it wouldn't likely still be in there by the time you got the airbox open. It will smell like fuel, though. In any case, unless you see a big accumulation of oil in the airbox or your engine consumes a lot of oil (more than a quart between changes, depending on how hard you thrash it) I wouldn't worry about it. Just wipe it out, put it back together, and ride it. :blah-blah

[roadrunner]

thank you steve, knee and rick for the input!!!

[kneedragger26]

Another possible cause for the stuff in the airbox is that the crankcase is usually vented to the airbox, so that any air that might enter the crankcase is clean (filtered). The flip side of this is that the natural blow-by gases, created by combustion pressure leakage past the rings, are directed up into the airbox via the crankcase vent hose. This creates a film of oil inside the airbox when the oil vapor condenses. Since you could acually see the stuff, I'd be inclined to think it's from blow-by, as fuel evaporates so fast it wouldn't likely still be in there by the time you got the airbox open. It will smell like fuel, though. In any case, unless you see a big accumulation of oil in the airbox or your engine consumes a lot of oil (more than a quart between changes, depending on how hard you thrash it) I wouldn't worry about it. Just wipe it out, put it back together, and ride it. :blah-blahGas. She said gas. I dont know what "stuff" is in the airbox. If the motorcycle had a crankcase breather problem the the emission from that tube would be pure motor oil.

EDIT: Crankcase blowby is caused by worn piston rings or a damaged cylinder. I.E. Overheating.

[kneedragger26]

even with the hydraulic(sp?) valves that are on the bike???
Hydraulic what? What kind of motor is it? A Honda V four?

[rickster]

The Nighthawk S, built in the 80's, used hydraulic followers (read no adjustment) to reduce maintenance costs and engine noise. Is that what you ride, Jennifer?
Perhaps I should've used the word "substance" instead of "stuff". This "substance" is again most likely condensed oil vapor that is not "pure" oil, but oil which has been diluted by fuel and combustion gases.
And the little tube or reservoir will fill up faster in rainy weather because there will be some water vapor that condenses in the oil after the engine cools. This water is returned to a gaseous state (steam) after the engine heats up, and is expelled from the engine along with the aforementioned blow-by gases. You might even see the "stuff" change color from that of dirty oil to a grayish shade.

[kneedragger26]

Perhaps I should've used the word "substance" instead of "stuff". This "substance" is again most likely condensed oil vapor that is not "pure" oil, but oil which has been diluted by fuel and combustion gases.
And the little tube or reservoir will fill up faster in rainy weather because there will be some water vapor that condenses in the oil after the engine cools. This water is returned to a gaseous state (steam) after the engine heats up, and is expelled from the engine along with the aforementioned blow-by gases. You might even see the "stuff" change color from that of dirty oil to a grayish shade.
K. Whatever you say. I personally dont care.

Now why would fuel get into the airbox? I thought thats where we started?
Combustion gases in the airbox? This happens when the crankcase pressure is high due to worn rings or a damaged cylinder. (Thats not normal)
By the way, fuel or fuel vapor in the crankcase is also not normal.

I have been doing engines all my life, so I will be sure to turn the other way when your giving technical advice.
Its sounds about as "gray" as the "substance" you are talking about.

Please dont be offended but it sounds to me you do not know what you are talking about.

[roadrunner]

Hydraulic what? What kind of motor is it? A Honda V four?
valves... inline 4..

[roadrunner]

The Nighthawk S, built in the 80's, used hydraulic followers (read no adjustment) to reduce maintenance costs and engine noise. Is that what you ride, Jennifer?
Perhaps I should've used the word "substance" instead of "stuff". This "substance" is again most likely condensed oil vapor that is not "pure" oil, but oil which has been diluted by fuel and combustion gases.
And the little tube or reservoir will fill up faster in rainy weather because there will be some water vapor that condenses in the oil after the engine cools. This water is returned to a gaseous state (steam) after the engine heats up, and is expelled from the engine along with the aforementioned blow-by gases. You might even see the "stuff" change color from that of dirty oil to a grayish shade.
right on!! mines not the s model but same deal... :) and you describe the stuff just right.. its an oily gas type of mess that indeed seems diluted with fuel and etc.. it smells right away of gas but i got my hands into it and it is for sure a mixture.. also, it has been known to change color. so, if the tube and holder deal were to fill completely, would that stuff back up into the motor?? not that i ever let it get to that point... (i had the chance to get one of the s nighthawks but got lucky and into the one ive got now. i wondered how the shaft drive would do. sure wouldnt be any chain mess though part of what i like of my bike now is doing chain stuff. thank you!

[kneedragger26]

valves... inline 4..OK. Its what I thought.

The oil in the airbox happens when the crankcase pressure is high due to worn rings or a damaged cylinder. (Thats not normal)
By the way, fuel or fuel vapor in the crankcase is also not normal.

If its an overhead cam and a shims over buckets setup, then you have lost the clearance between the intake cam lobe and the shim. Hence the gas sitting in the airbox.

The only way it comes out your of the carbs is that you have lost your valve adjustment.
Also the rings are letting oil past the rings into the combustion area. I bet its coming from the crankase.

The gasoline is from the intake valves opening to early from clearance.

If the motor is worn, then it will also be blowing oil from the crankcase into the airbox from the breather tube. Crankcase pressure is measured with a manometer. (H2O)

I pretty much done talking about this online. Check your valve clearance or get someone to do it for you. You will be surprised.