Newly rebuilt carb still leaking

[adamwade]

Alright, I have exhausted my ideas.  I have tried 3 different carbs and still have the same problem.  Here is what I have done so far:
* Installed 2 carb rebuild kits from Parts N More
* Checked 4 different floats to see if they were damaged
* Replaced all o-rings and gaskets, float needles etc.
* Checked float heights on both bowls
* Ran/replaced all new 5/16 fuel hoses
* Used entire can of carb cleaner

Bike starts and runs great.  After I turn the engine off, and shut-off is still in "ON" position, nothing happens.  After the bikes sits for 3 or 4 hours, fuels starts leaking from the back, and coming out of my K&N filter.

[VTNewb]

What do the plugs read? This happens on both my bikes with a rich condition.

[se7enty7]

can this be from a bad petcock?

[adamwade]

Spark plugs?  Brand new replaced yesterday.
Fuel mixture screws are set 3 turns out.

My only other options are to begin on the fuel tank and/or frame petcock valves.

Just wanted to get some information.

[VTNewb]

What color were the old ones?

[adamwade]

Plug ends looked pretty fouled when I pulled them.  They were pretty much black and covered.  I know that the previous owner said the bike ran rich, so when I rebuilt the carbs, I made sure I only turned the screws out 3 turns.

[adamwade]

Any other ideas?

[MarkusN]

Do carb rebuild kits replace the needle valve seat? If not, that could be the cluprit. Only if the petcock is also leaky, however.

Checked fuel hose routing? I just heard weird stories about someone who had the overflow drain connected to the reference pressure T, so I start to consider anything possible.

[adamwade]

Yep, fuel lines are all routed properly.  The carb rebuild kits did come with new float needles and they have been replaced.

[Kerry]

MarkusN was actually asking about the large brass item in the kit (where the needle gets "seated") but I assume you changed that too....

[adamwade]

Yes, Kerry, everything in that kit was swapped out.  I feel like I'm down to the two petcock valves now.

[MarkusN]

The petcock alone can not cause flooding. Even if it is open, fuel flow should still be controlled by the float valve.

[adamwade]

You would think, but I have tried three different carburetors, and have had the same results.  I dumped most of the gas from the tank and put a flashlight in there to see what I could find.  I noticed that the fuel filter part of the tank petcock is not attached (busted off?) and is just floating around in the tank.  Could that be the culprit?

[MarkusN]

Well, having heard that I'd assume that fuel is seeping down along the hose, not throgh it. With that defect it may very well be that the whole filter/petcock assembly is not tight against the tank.

[adamwade]

All fuel lines are bone dry at all times.

[MarkusN]

OK, thinking out of the box here.

Suppose your tank vent is tight. And I mean tight. Fuel vapor pressure might build up enough to force fuel past the petcock membrane and the needle valve (both have only finite conterpressure). Especially with a nice and hot engine under the tank after a longish ride.

How to test: Let the bike sit until you notice fuel dripping from the carbs again, then open the tank cover and listen for a hiss.

Let the bike sit with the tank cover open and check if it still seeps.

[adamwade]

Anything is worth a shot right now.  I am also going to try and get an aux fuel container and hook it directly to the carbs and see if they still leak.

[Kerry]

QUESTION:  Is there any difference in the float height between the time you first turn off the engine and then 3 hours later?

The first measurement will show you the height at which the floats "close" the needle valves.  The second measurement should show you whether the floats have been pushed even higher by additional fuel allowed into the bowls by (assumed leaky) needle/seat combos.

NOTE:  You may have to leave the "U tube" in place and the drain spout open for all three hours.  If you don't, then opening the drain spout and letting fuel into the U-tube after the 3 hours may drop the floats back down to where the height looks OK, and they won't climb back up until additional fuel has slowly seeped into the bowls.  Make sense?  :dunno:

[adamwade]

Not sure what you mean by U-tubes and drains.  Are you talking about the float bowl drains?

[Kerry]

I'm talking about the non-invasive method of measuring your float heights.