Fuel from carb air vent hose

[SunshineNomad]

I went in to replace a cracked fuel intake hose (left). I hooked up an aux tank to check the new hose. Turning it in, I found that a steady stream of fuel leaks from the left side “air vent hose” from the swivel T between carbs 3 + 5 Can anyone tell me the cause?  Maybe a stuck float?  I really hate to remove the carbs.  

[SunshineNomad]

Here’s a pic from the manual

[98valk]

Here’s a pic from the manual

that's a flawed pic from the manual, same as manual I have. flawed because the bowl overflow tubes should have a bend in the open end so they both can be installed into the holes in the carb crossover frame to secure them in place which will ensure proper air flow and preventing any chance of hydro-loc. My '98 has tubes as I described.

If u have fuel coming out of them then that would indicate the petcock is not stopping fuel flow and the floats and needle and seat are working preventing fuel flow into the carb throat.

[SunshineNomad]

Im my pics, the tubes are out of the holes trying to figure out why. I did think one or more float valves are stuck. I’ll give the bowls a whack and see if they start working.

[98valk]

Im my pics, the tubes are out of the holes trying to figure out why. I did think one or more float valves are stuck. I’ll give the bowls a whack and see if they start working.

The manual shows early '97 pic, those tubes are wrong and I guess were replaced with curved end tube in '98. even the parts houses shown the tubes curved.
 
the float needle valves are doing what they are suppose to be doing. nothing wrong with them. your petcock is not shutting the fuel off causing the bowls to overfill.

[SunshineNomad]

Ah yes. That makes sense but why only on one side?

[Avanti]

On kickstand. Set it straight up and then see what it does.

[Jims99]

You should not get fuel from the air tubes even if the petcock is not working. The float valves should prevent fuel from overflowing. The petcock is a backup shut off. If you’re getting fuel out of the overflow, be very careful not to hydrolock the engine. Personally I would pull carbs and clean and also update the float valves with KL 18-8955. They have a stronger spring to help prevent overflow.

[98valk]

You should not get fuel from the air tubes even if the petcock is not working. The float valves should prevent fuel from overflowing. The petcock is a backup shut off. If you’re getting fuel out of the overflow, be very careful not to hydrolock the engine. Personally I would pull carbs and clean and also update the float valves with KL 18-8955. They have a stronger spring to help prevent overflow.

""also update the float valves with KL 18-8955.""

Randakk https://www.randakks.com/   has stated over the yrs anything other than the OEM float valves is a downgrade.

Furthermore a stronger spring has nothing to do with preventing overflow.  there is a metal raised area around the plunger that contacts the float resulting in a hard surface to surface contact to positively shut off fuel full via the needle into the seat. the plunger and spring only function during operation. this is how float valves work.

see raised area.

[Itinifni]

Jims99 is correct regarding fuel from the vent hoses, both your petcock and at least one float valve require attention.

The purpose of the vents is simply to expose the bowls to atmospheric pressure, they are not designed to serve as overflows.

I have no experience with any of the aftermarket float kits as I have only used OEM.

[98valk]

Jims99 is correct regarding fuel from the vent hoses, both your petcock and at least one float valve require attention.

The purpose of the vents is simply to expose the bowls to atmospheric pressure, they are not designed to serve as overflows.

I have no experience with any of the aftermarket float kits as I have only used OEM.

both of u are incorrect. the bowl vent line is also an overflow line for when the float needle and seat valve fails. properly installed overflow/vent line and not clogged prevents hydro-lock

[Itinifni]

98Valk,

Do you have a reputable source stating the vents also function as overflow lines?

40+ years as a master technician I've serviced quite a few carbs, I've never seen a vent that would function as an overflow, of course that doesn't mean they don't exist.

Usually, the vent is well above the venturi and transfer ports meaning any fuel that reaches the vent is already flowing into the intake manifold.
As I look at the diagram in the OPs first post I see lines and even the 3-way joints are clearly well above the air funnels.

I don't see how they would keep fuel from running into the cylinder if the petcock and float were both stuck open.

[SCain]

Here’s a pic from the manual

This pic looks like California carb set where the vent tubes are not curved.

[topgunfs]

I recently had this happen, I had removed on set of carbs to service them and installed a set I had as back up.  When I started the bike I had raw fuel entering the the air tube coming from the port (left) side flowing through the carb air solenoid and into the drain/atmospheric pressure tube. 
I took the carbs off and bench tested them, handing a fuel source with a cutoff, and every time I opened the fuel I got raw fuel from the left bank into the air tube.   I removed the bowls and wa la.
The problem was a float needle was stuck in the open position allowing fuel to to over fill and enter the air channel.  cleaned the fuel entry port, back flushed the fuel entry channel, inserted a  new float needle  and reinstalled.  Problem solved.

[98valk]

98Valk,

Do you have a reputable source stating the vents also function as overflow lines?

40+ years as a master technician I've serviced quite a few carbs, I've never seen a vent that would function as an overflow, of course that doesn't mean they don't exist.

Usually, the vent is well above the venturi and transfer ports meaning any fuel that reaches the vent is already flowing into the intake manifold.
As I look at the diagram in the OPs first post I see lines and even the 3-way joints are clearly well above the air funnels.

I don't see how they would keep fuel from running into the cylinder if the petcock and float were both stuck open.

So I finally had some time to pull out my low 7k mileage spare set of carbs.
 I removed the bowl cover and float of one carb.
 There are two separate and about the same size holes in the top of the bowl carb body.  the highest one from the bowl cover would be the vent. This can be seen on the outside of the carb body as a half round tube cast into the carb body and has a brass manufacturing drill plug at the bottom of the body.
  The second lower one which is closer to the bowl cover would be the overflow. It can be seen also, but is a much shorter round tube and is right behind the air cut-off valve.
 Both holes tie into the one vent/overflow line in the upper carb body.

[Itinifni]

The number or location of the passages in the body is irrelevant if the fuel has to pass through the vent tubes. If that's the case the fuel level will already be above the venturi and flowing into the manifold.

If for example the intake valve was closed and the petcock and float needle open (on the same cylinder), I can imagine fuel flowing fast enough to overflow through the vent hose. However it would also be filling the manifold. In that scenario, hit the starter and bad things can happen.

Now if the lower openings provide a path for fuel to exit the carb that does not rise above the venturi, then they may prevent overflow from entering the intake manifold.

There's a reason Honda calls them "Air Vent Tubes".

[98valk]

The number or location of the passages in the body is irrelevant if the fuel has to pass through the vent tubes. If that's the case the fuel level will already be above the venturi and flowing into the manifold.

If for example the intake valve was closed and the petcock and float needle open (on the same cylinder), I can imagine fuel flowing fast enough to overflow through the vent hose. However it would also be filling the manifold. In that scenario, hit the starter and bad things can happen.

Now if the lower openings provide a path for fuel to exit the carb that does not rise above the venturi, then they may prevent overflow from entering the intake manifold.

There's a reason Honda calls them "Air Vent Tubes".

Honda calls many things by unusual names/terms.   open up a carb on the bench, too see how u are incorrect.

[Mooskee]

You should not get fuel from the air tubes even if the petcock is not working. The float valves should prevent fuel from overflowing. The petcock is a backup shut off. If you’re getting fuel out of the overflow, be very careful not to hydrolock the engine. Personally I would pull carbs and clean and also update the float valves with KL 18-8955. They have a stronger spring to help prevent overflow.

""also update the float valves with KL 18-8955.""

Randakk https://www.randakks.com/   has stated over the yrs anything other than the OEM float valves is a downgrade.

Furthermore a stronger spring has nothing to do with preventing overflow.  there is a metal raised area around the plunger that contacts the float resulting in a hard surface to surface contact to positively shut off fuel full via the needle into the seat. the plunger and spring only function during operation. this is how float valves work.

see raised area.

It is a real shame they put those springs in there. What a waste!

[98valk]

You should not get fuel from the air tubes even if the petcock is not working. The float valves should prevent fuel from overflowing. The petcock is a backup shut off. If you’re getting fuel out of the overflow, be very careful not to hydrolock the engine. Personally I would pull carbs and clean and also update the float valves with KL 18-8955. They have a stronger spring to help prevent overflow.

""also update the float valves with KL 18-8955.""

Randakk https://www.randakks.com/   has stated over the yrs anything other than the OEM float valves is a downgrade.

Furthermore a stronger spring has nothing to do with preventing overflow.  there is a metal raised area around the plunger that contacts the float resulting in a hard surface to surface contact to positively shut off fuel full via the needle into the seat. the plunger and spring only function during operation. this is how float valves work.

see raised area.

It is a real shame they put those springs in there. What a waste!

the guy who built the turbo valkyrie was adding an extra external spring to the plunger/needle to float interface thinking the plunger was closing the floats needle/seat area. I was showing it is a mechanical connection causing full closure of the needle/seat and always has been in carburetors.