Topic: Should fuel be coming from both petcock tubes???(stupid question)

[ericmu17]

Should fuel be coming from both petcock tubes??? I have fuel coming from the front tube but only a very slow drip from the other one... If it is clogged whats the best way to unclog it. I just noticed this today.... I think It could be the source of my "carb issues".

[mjstone]

Try holding your thumb over the tube that flows, to block it off, and see if more fuel flows out of the other tube.

MJ

[lone*X]

Obviously since they both feed carburetors, fuel should be coming from both equally.  If the petcock is in good shape otherwise, rebuild kits are not expensive.   I have  rebuilt several over the years with excellent results,   It would be a good thing if you told us what model and year you are working on as well.  It helps getting the right information since there are several different types of petcocks, dual outlet, single outlet, flange mounted, bung mounted, screwed together, riveted together, etc.

[Grabcon]

This is interesting I hope someone solves this or at least explains it. I have the same issue with my K4. I have clear gas lines so I can see the fuel. If I remove the lines and open the petcock I only get gas from one side. That would be for both the normal position and reserve. But when the lines are attached the gas flows through both lines. You can see the gas flow and the motor runs on all 4.

I have removed and cleaned the brand new petcock and it still acts this way. It drives me nuts why it works this way. This is very notice able when draining the tank.

[Raul CB750K1]

As stated above, as soon as the one that flows gets closed, fuel starts to flow from the other one. I should have to open a petcock to explain why, but it seems that gas simply gets out by the closest exit. When this becomes full, by the other one. When the gas tubes go to the carburetors, as soon as the bowl valve stops the gas, the other carb will start to fill.

After all, the pipe from where gas gets out of the tank is thinner than the petcock fittings. And as gas is gravity fed, the amount of gas out of the petcock doesn't vary whether there is one or 10 fittings. The time it takes to fill all bowls won't change whether there are two filled first and then the next two, or the four at the same time.

[TwoTired]

Kinda funny when you think about it.

As you walk down the street, gravity is always pulling you earthward.  Ahead of you, and in line along your walking path, are two open manholes, and you wonder why you don't fall into the second one.  Cover or fill the first encountered manhole and you will. 

[Gordon]

To paraphrase:  It's completely normal and nothing to worry about.

[lone*X]

Odd, as many times that I have drained my 550k1 tank with dual outlets I have never noticed this affect.  I tend to keep my tanks full so maybe the increased weight/pressure  from a full tank more equally distributes the fuel flow?  Interesting indeed.

[Roach Carver]

Kinda funny when you think about it.

As you walk down the street, gravity is always pulling you earthward.  Ahead of you, and in line along your walking path, are two open manholes, and you wonder why you don't fall into the second one.  Cover or fill the first encountered manhole and you will. 

this may be my favorite explanation of anything ever. EVER.

[Bankerdanny]

It may be that when the engine isn't running the fuel naturally tends to flow from one side, but when the vaccum is present from a running engine to draw fuel up from the bowls that small draw pulls the fuel through the second line.

[Pat_at_APE]

The simple answer is that fluid always takes the path of lease resistance.  Fuel flows out of whichever line is the easier path.  Maybe one hangs lower so a siphon effect if happening and favoring that line. 

May favorite is the manhole cover analogy.   Too funny...

Pat

[TwoTired]

It may be that when the engine isn't running the fuel naturally tends to flow from one side, but when the vaccum is present from a running engine to draw fuel up from the bowls that small draw pulls the fuel through the second line.

As the float bowls ARE vented to the atmosphere, very very near the float valves in the carbs, there is no engine vacuum that reaches the fuel valve outlets.

Next contestant, please.   

[Grabcon]

I do like the manholes but Pat At Ape is a might bit funnier. "Maybe one hangs lower" Well mine do and it has nothing to do with fuel line.

So what I have read above it is clear that no one really knows why, but what we do know is that somehow it just works. So just don't worry about it.

[Roach Carver]

I think its actually clear how it works. The two outlets share one inlet. The fuel flows out the nearest hole. When that hole is filled i.e. The two carbs fill, then the other two get the flow.

[Gordon]

So what I have read above it is clear that no one really knows why, but what we do know is that somehow it just works. So just don't worry about it.

This doesn't have to be some weird mystery.  There is one inlet for fuel from the tank and two outlets.  Unless the petcock is sitting dead level, one outlet will always be slightly downhill from the source, and liquids flow downhill.  If there isn't anything attached to the outlet to slow or stop the flow, like fuel line and a rack of carbs, the gas will continue happily flowing from the one that is downhill. 

[TwoTired]

Wait.  No one has mentioned the brand of gas, whether it has ethanol in it, or platformate,  ...or wait, why didn't I think of this before ... LEAD!
Maybe the lead was needed back when the these bikes were made, so the gas would have enough weighted momentum to reach the second outlet?

Maybe...  

Perhaps we can rename the forum Camelot?

Monty Python-Camelot Song

[Killer Canary]

Is a duck heavier than fuel though?