3rd Gen gas leak: possibly around the part in this diagram

[MagnaMan]

Lately, my mileage has dropped every so slightly, and  I have been smelling gas when putting the bike up after commuting home. Today I noticed a small amount of liquid on the chrome cylinder head dressing (back right cylinder when sitting on the bike). I got some on my fingers and walked away from the bike to sniff it. It's definitely gas.

I started feeling around and this one little vacuum type unit is filthy and directly above the cylinder. It's covered in a moist, sooty gas smelling mixture. (See the highlighted item from the diagram manual.)

It may just be a bad line since the bike is a '99 and spent most of its first 6 years setting up. I intend to take the tank off on Friday and see what I can find out, but I was wondering a few things:

1. Anyone else experience this? If so any advice?
2. What is that part in the diagram? Can't seem to find a specific name for it in the service manual.

Thanks,

Jesse

[Greg Cothern]

From the diagram it looks like you have highlighted the fuel diaphragm shut off.  
It is a vacuum operated item that shuts fuel flow when there is no vacuum present.
I dont recall seeing one leak before, but your airbox vent is pretty close, check that as well.
Hope some of this helps.

[Dlcarrales]

Jesse,

I ride a 1996, I had similiar problem that originated from the left hand side.  After trying to isolate it, we determined it was coming from the carbs. We replaced the gasket around the float chambers (All 4 since 2 of them were very worn. This took care of the problem.  I went ahead and put a K & N Filter on also at this time since I had it apart.

I will try to attach a pdf, it is gasket (O-Ring #10) in manual page 5-8.

Hope this gets you on the right track.

[MagnaMan]

Hey David. Thanks for the the tips.

OK. I am 99% sure it is the fuel diaphram shutoff valve.

First it is the item that is wet and dirty.

Second, I saw it leaking while the bike was running.  

It's a slow drip. I took the unit off and inspected the two fuel lines. They appear to be in good condition and they sure were stuck on tight so I don't think the leak was at their connection to the unit.

Inside the unit is a post with two diaphrams on each end. It simply toggles back and forth shutting off fuel. Now the diaphram seating area is  a little dirty with some small rust particles that came from the tank (Remember the bike sat a lot before I bought it). The large diaphram also has a wave in it. Meaning it doesn't uniformly flip one way or another. It will curl. I'm not sure if it means I should replace this.

Here's my theory:
If the diaphram isn't sealing right then the fuel wouldn't shutting off.  Not that big of a deal since I use the petcock regularly.

But since it's leaking while running, then perphaps the unit just has some junk inside that's keeping the whole thing from forming a tight seal. Maybe if I just clean this out well inside and put it back together tightly my problem might be fixed.

Any thoughts?

[Dlcarrales]

Dont know if I can help you with that.  I guess it is worth a try.  Good Luck and let us know if it fixes the problem.

[MagnaMan]

That appears to have fixed it. No more leak.

David, thanks again for your help and thanks to Greg for identifying the mystery vacuum valve. I was lucky in that it was an easy leak to spot and relatively simple -- compared to pulling the carbs.

On to the next tasks: installing my modified pipes and a VTX headlight.

[MagnaMan]

OK. Well that didn't fix it.

I put my modded pipes on last night and took it for a ride to get some gas. With a full gas tank she leaks even worse now after I took it apart and cleaned it.

I talked to the Honda parts guy and he said that unit uses the diaphram also as the gasket... so it can leak easily when it get's old.  When I had it apart I noticed it had no gasket sealing surfaces and thougt was a poor design.

I was thinking about taking the unit back apart and applying a light layer of silicone to seal the surfaces, but getting all those hoses off is such a pain and I don't want to do it a 3rd time if the silicone doesn't work... so I ordered the replacement diaphram unit for $40 from the dealer. (It was $30 online plus shipping so it was nearly a wash).  

Of course another alternative is to bypass the vacuum valve altogether and just rely on the petcock, but since the part is only $40 I figured it wouldn't kill me.

[Curtis_Valk]

Hopefully this will be the end of it.  I know you would like to put this problem to rest so you probably did the right thing by biting the bullet.  Good luck from one Halloweenie to another.    

Curtis

[MagnaMan]

Thanks Curtis.  Us halloween bikers do have to stick together

Yeah I hope this is the end of it.  I haven't been on a good long ride in a while.  I'm going through withdrawal!