Fuel streaming from Evap Cav Control Valve CB750

[Skypuppet]

1995 Nighthawk 750

I recently had the carb off for cleaning. Reinstalled, bike runs, but now have a small stream of fuel flowing steadily from the vent line on the Evap Cav Control Valve. Reference the diagram under the seat for the California emissions vacuum hose routing—-this is the line labeled (7), "To Open Air".

Before I pull tank back off and double check tubing, any quick answers on where to start in terms of something disconnected or misconnected or malfunctioning? 

The vacuum fuel selector appears to be in good shape, but I'll check the diaphragms again.

Stuck float?  Carbs been disassembled, cleaned, and ultra sonic'ed, so I wouldn't think so. 

Thanks,
Chris

[Bob H]

bike runs, but now have a small stream of fuel flowing steadily from the vent line on the Evap Cav Control Valve.

I assume you have a stream of fuel flowing when the engine is off?

The vacuum operated petcock on the 750 should not let fuel flow in any position without vacuum supplied to the petcock, so if you have a steady flow of fuel, the petcock is not doing it's job.

Downstream, the float bowls should HALT the flow of fuel. Period.
Is this a California bike? Just curious where the fuel is running beyond the first 2 lines of defense.

[mollusc]

Not really familiar with the California hose setup, but as noted above, if fuel is flowing when the engine is off then both the petcock and the float valves are not doing their jobs.
It's very easy for float valves to stick after a cleaning.  Don't be fooled into thinking that can't be the problem.

[Skypuppet]

Sorry—to clarify, fuel streams from Evap Cav control valve vent only when bike is running.  The petcock seems to hold a vacuum, and no trouble getting bike to start and run. The stream of fuel is low, but steady, and not just a fast drip.

Bike came from California and has the emissions tubing mess. I will double check the routing of the tubing next.

[Bob H]

Bike came from California and has the emissions tubing mess.

My 750 was also California.
Your leak has nothing to do with the CA emissions - but it is manifesting there instead of somewhere else.
If it only leaks while running, it is your float bowls or the connector pipe between the carbs.

Did you change the O-rings between the carbs??

[Bob H]

California diagrams below

[Bob H]

... but now have a small stream of fuel flowing steadily from the vent line on the Evap Cav Control Valve.

When the float bowl overflows on a 49 state NH 750 (or 84-86 700S uses same carbs) the gas will run out the rubber hoses that I marked with an arrow below.
These are "vent lines" as you mentioned, and the purpose is to vent the float bowls, let air it as fuel is consumed.

With a California model, those hoses are much longer and connect to a rat-nest of emissions garbage. In the diagram above, part 20 is that vent hose.



I can show you how to get rid of the emissions garbage if you are interested.

[mollusc]

From those diagrams it looks like the only way fuel can get to where you're describing it is if it's exiting the carbs via the upper breather pipes.  I can't even imagine how fuel is getting all the way up there but it sounds like a thorough cleaning is in order.  May be an opportunity to turn it into a 49-state at the same time.

[Bob H]

I can't even imagine how fuel is getting all the way up there but it sounds like a thorough cleaning is in order.  May be an opportunity to turn it into a 49-state at the same time.

Yeah, he may have fuel running into the engine as well.
I haven't had that happen, but have heard that it is a potential issue.

An abundance of caution would be 1) pull the plugs and turn the engine over by hand (rear wheel) to make sure a cylinder isn't full of fuel. Apparently you can bend a rod or really screw things up if liquid can't compress.

2) check the oil for presence of gas, does it seem normal.

I did turn mine in to 49 state carburation, and could post a "how to" when I get a couple home repair projects wrapped up.

[Skypuppet]

Okay, I went ahead and pulled the carb off, poked and prodded the floats and anything else that moved, occasionally nodding my head knowingly in case anyone was watching. Then I reinstalled the carb, doing a much better job the second time around. Double checked hose routing, threw tank back on, and she fired right up and ran normally.  May need to be tuned, but no more fuel dribbling. I have no idea what I did wrong the first time, or how I may have fixed it, but do appreciate all the responses—very helpful.

I am interested in the emissions system removal procedure.

[Bob H]

...pulled the carb off, poked and prodded the floats
...I have no idea what I did wrong the first time, or how I may have fixed it

I am interested in the emissions system removal procedure.

Sometimes a stuck float can be remedied simply by tapping the side of the carb float bowl with a piece of wood, or handle of a screwdriver.
Once they are oriented properly, and functioning, you shouldn't have any more trouble with it.

I will do a separate post on the CA emissions, but won't be able to get to it right away.