How does the float bowl vent work?

[Dale_K]

I see the drain valve screw but I don't understand the vent function.  Where is the passageway that vents the float bowl chamber?  I'm guessing it discharges through the nipple where the rubber drain hose connects but I don't see where the other end of this passageway emerges up inside the carb.  From the pictures and videos I can't see a hole in the bowl that would act like an overflow.

Maybe somebody who has extra carbs laying around could take a picture.  Seems like there must be a vent to the atmosphere in the upper area of the bowl chamber, otherwise it would be hard for the fuel to flow into an empty bowl as the air space filled up and became slightly pressurized.

I cam remember old Amal carbs with the float bowl tickler and how the gas would overflow out a vent hole once the carb became completely flooded and I'd expect some kind of similar vent on our carbs.

Basically I'm trying to protect against hydrolock and ensuring a working overflow system might be easier and more fail safe than hoping the float needle works perfectly forever. 

[Ricky-D]

Forget about that!  If a working "overflow" vent system would prevent a "hydrolock" we would never be reading about a hydrolock on the forum.

Replace the stock petcock with a good Pingel petcock and you will be a lot closer to absolute protection than any of the "prevents" that have been
suggested in your other posts about the same subject.

You can be in denial all you want but there in nothing going to protect you from "hydrolock" except your own determination and persistence.

As far as worrying about your ability to remember to shut off the gas, well, if you think that'll be a problem you ought not be riding a motorcycle
then, due to your lack of mental acuity.

***

[Gavin_Sons]

watch this, I still believe the petcock has little to do with hydrolock. I have a pingle and still happened to me a few weeks ago. This dude knows his stuff. This is on the turbo bike he did a year or so ago.


https://youtu.be/QwJdnA5l8cQ

[The emperor has no clothes]

You are bound to hear from many "experts" on this. Read what you can about it and make your own determination. I guess according to some I shouldn't have been riding for the last 46 years. 

[Gavin_Sons]

You are bound to hear from many "experts" on this. Read what you can about it and make your own determination. I guess according to some I shouldn't have been riding for the last 46 years. 

 

[WintrSol]

I see the drain valve screw but I don't understand the vent function.  Where is the passageway that vents the float bowl chamber? 

The air vents are connected through the air tubes that connect all three carbs at the top of each bank, with one vent tube in each bank a 3-way tube, the other just a straight tube, all sealed by O-rings. The 3-way tube is where you connect the vent line. This is for allowing the air in the bowls to exit the bowl chambers when the bowls fill only, it does not provide overflow protection. See pages 5-16 and 5-17 of the service manual. The exploded drawing on 5-16 does not show the 3-way tube, but all four as straight tubes, BTW.

As the linked video shows, the primary failure in most hydrolock conditions is one or more float/float valve assemblies; if the fuel valve is open (or the pump running, in his case), a bowl can overflow, even if the engine is running. When the engine is off, it takes a second failure to cause overfilling: the stock petcock sticks open when the engine is off, or the off position isn't really off. A manual petcock will prevent overfilling when the engine is off, but not when it is running. Since hydrolock usually occurs when the engine is off, it takes both failures.  It would be great if Honda had specified a fuel level measurement that may be done without removing the carbs, by connecting a clear tube to the drain and turning it up in a J shape, then opening the drain. With that, you could quickly check for a failing float valve during regular maintenance.

But, there is another path to hydrolock with a vacuum-operated petcock: the vacuum diaphragm fails, allowing fuel to flow directly to the vacuum source. No float valve failure required.

[Pete]

Please do not confuse the carb bowl drain and hoses with the carb vent and hoses.
They are 2 different systems and function independent of each other.

The carb bowl drain and hoses (optional) drain the carb bowls only if you loosen the external screws on the bottom of each carb bowl.

The carb vents require no operator action, on each side 3 carbs are connected to each other via hollow metal sleeves in the carb bodies then to 1 rubber hose on each side that goes up and turns at a right angle to the rear and rest on a frame stay under the gas tank above the carbs. The rubber hoses are open to atmospheric pressure, so air or gas can escape.

When a petcock and/or carb float fails and gas flows with enging not running it should flow out thru the carb vent hose rather than hydrolock and dump on the center engine block. That does not always happen because in some cases there is less restriction thru the carb into the engine than into the carb vent systems and so you have hydrolock.

I see 2 engineering flaws with the carb vent system, to much resistance to flow (vent to high) and dumping gas onto an engine block.

On a very slow gas leak over a long time the carb jets leak gas into the engine slow enough to never activate the carb vents, so they are ineffective at preventing hydrolock until the cylinder has filled. And then the carb vent overflows, warning of a hydrolock, but not preventing one.

On a faster gas leak the carb vent does overflow faster than the cylinder fills, but given enough time and gas it could still hydrolock.

Hope this helps.

[Dale_K]

Thanks for the explanation.  Somehow I misunderstood the vent and thought it was combined with the drain but I didn't see how that could work, thus the post requesting more info.

Reading the other threads I recall some info that pertained to Gold Wings and their carb vent system.  Something about the rubber vent lines forming a trap that kept the vent system from functioning properly.  It looks like something similar could happen on a Valkyrie since the rubber vent lines could also form a trap.  What would be the downside to completely removing all the rubber vent hoses from all the carbs?  I could see how there could be some gasoline seepage onto the motor but I could accept that.  It might even be better in the sense that you'd have some knowledge that the float level is dangerously high.  Plus you might be able to pinpoint which carb was the culprit.

[Leathel]

watch this, I still believe the petcock has little to do with hydrolock. I have a pingle and still happened to me a few weeks ago. This dude knows his stuff. This is on the turbo bike he did a year or so ago.


https://youtu.be/QwJdnA5l8cQ

the manual says to check the float heights and replace the float & valves if not in spec.... I didn't check mine and I wish I did as the valves did leek with extra pressure, I am going to replace all the float valves, after that if the float level is out I might try that....or just heat the plastic and bend it until its right before assembling this time ..... then I can go back to bigger fuel lines for optimum flow

Replacing the Tap will not stop the float valves leaking but if the shut off valve is fitted and is close enough to the carbs it limits the amount of fuel getting into the engine so its shouldn't have enough to totally flood the pot and hydroloc...

[Pete]

The vent issue has occurred on other motorcycles, usually when the hoses are run to hang low on the bike where road water splash can enter the lower end of the hose and get trapped by negative air pressure in the system. (usually tank vent not carb vent)

This has also happened on fuel tank vents for the same reasons. On fuel tank vents a small hole drilled into the hose resolves the issue.

[98valk]

watch this, I still believe the petcock has little to do with hydrolock. I have a pingle and still happened to me a few weeks ago. This dude knows his stuff. This is on the turbo bike he did a year or so ago.


https://youtu.be/QwJdnA5l8cQ

he is wrong about how the spring and plunger are closing the float valve.

see my post and pic of valve
http://www.valkyrieforum.com/bbs/index.php/topic,93751.msg931886.html#msg931886

[jim@98valkyrie.com]

You are bound to hear from many "experts" on this. Read what you can about it and make your own determination. I guess according to some I shouldn't have been riding for the last 46 years. 

And yet, the man, the myth, the legend lives on.....

[Pete]

But, there is another path to hydrolock with a vacuum-operated petcock: the vacuum diaphragm fails, allowing fuel to flow directly to the vacuum source. No float valve failure required.

There is more to this.

The fuel diaphragm must fail, leaking gas into the chamber between the fuel and the vacuum diaphragm and the drain that is in the chamber is clogged or is overwhelmed by the volume of the fuel diaphragm leak. Then a hole in the vacuum diaphragm will flow to the vacuum source. 

[WintrSol]

But, there is another path to hydrolock with a vacuum-operated petcock: the vacuum diaphragm fails, allowing fuel to flow directly to the vacuum source. No float valve failure required.

There is more to this.

The fuel diaphragm must fail, leaking gas into the chamber between the fuel and the vacuum diaphragm and the drain that is in the chamber is clogged or is overwhelmed by the volume of the fuel diaphragm leak. Then a hole in the vacuum diaphragm will flow to the vacuum source. 

Yeah, I simplified too much. If the vacuum diaphragm fails, it is probably because it is exposed to fuel from the rest of the petcock failing. A cascade failure, if you will. I'm just glad I don't have to worry about any of this - my petcock is disabled, except for the reserve function, which just drains the remaining fuel into the belly tank. There's been a few occasions in the few years I've had the bike that the extra range made a difference, too.