Topic: All my petcocks leak. I'm up to seven now. I've switched parts

[mycb750k6]

CB750 K1 with petcock with two fuel tubes on right side of tank.
I'm up to seven petcocks now. I've switched parts around, bought ebay petcocks, bought rebuild kits and finally bought a new NOS petcock and it leaks too. They leak from the rear brass tube. Maybe it's not the petcock? what else could it be?
I'd kill for a petcock that doesn't leak right now. Why does fuel drip from the rear tube when the fuel is shut off?

Can I just plug the rear tube and run a T from the front tube like the later 76 and F model petcocks do?

[Johnie]

I have seen a number of these leak from poor gaskets that are under the screws that hold the petcock to the tank. I have replaced these gaskets on all 3 of mine and have never had another leak.

[mycb750k6]

OK but this is a new petcock and gasket. It does suggest the tank is irregular under there though as every petcock leaks and only on this tank. I'm going to try to sand or file that area while trying to keep anything from going in the tank.
That's a weird gasket anyway and not one I've found in rebuild kits. My H/W sells metric O-rings. Maybe I can find a fat one.

[Old Scrambler]

+1 with Johnie..........New gasket-washers or cut your own by slicing an O-ring will stop that type of leak.

[mycb750k6]

OK

[srook]

I found that o-rings under the screws will distort as you tighten them.  I have used copper washers from McMaster-Carr.  I bought a big bag of 6mm copper washers and they work great for sealing the petcock.  I also replaced the screws with allen heads.  This allows you to really tighten those suckers down.
Scott

[mycb750k6]

I'm still leaking. I don't have O-rings under my screws. I have fiber washers in all the petcocks I've collected including the new one I just bought . But anyway, how would these washers leaking cause fuel to leak from the brass supply tubes? I bought new allen heads and new washers and I'm ready to tighten it down but I guess I don't understand how this petcock works and why fuel is coming out of the brass supply tubes. I'm becoming annoyed at my inability to correct this.

[Terry in Australia]

Don't beat yourself up mate, I've got a newish petcock on my K1 tank with a new rubber seal in it (OEM Honda part) and it leaks from the rear pipe too. #$%*ts me to tears, but my carbs don't leak, so I don't worry about it. If I need to take it off, I just run a piece of fuel line between the two pipes. Cheers, Terry.

[mystic_1]

Do you mean that gas leak THROUGH the rear brass tube (internal leak) or that gas leaks AROUND the rear brass tube (external leak)?

Sounds like you're checking these without fuel lines attached?  Just want to be sure we're on the same page.

mystic_1

[Terry in Australia]

Fuel drips from the rear pipe. From inside it. 

[Johnie]

If those screw gaskets leak they allow fuel to run down the side of the screw, off the head and into the deliver area. I like the idea of the copper washers. I have the fiber ones and have success with those? Can't figure out why you are still having a leak there? Are those fibers real tight to the screw shaft? The fiber washers I got from the hardware store were very tight and I actually had to screw them past the threads.

[mycb750k6]

That's the explanation I was looking for. The gas leaks by the fiber washers into the fuel delivery area and then out the brass delivery tubes - really,.. really? OK so I'll get out the allen stainless bolts and the breaker bar and have at it tomorrow with some new copper washers. I guess these old arthritic hands aren't what they used to be.

And no, it wasn't leaking from outside or around the petcock. It was coming out of the bloody tubes - as if I hadn't shut the gas off!! And I do have a pesky float valve on #1 that does want to dump gas on the floor occasionally when the bowl fills from a leaky petcock!!

[srook]

I'm not sure you will ever get it to stop dripping gas out of the tubes when the petcock is shut off but you should be able to slow it way down.  The floats should provide enough resistance to to not allow fuel to overfill the bowls.  I think all the petcocks drip but the floats don't allow the bowls to overfill and dump gas out of the overflow tubes.  Don't go too crazy cranking down the allens, I was half kidding.  The last thing you want to do is to strip out those threads.
Scott

[mystic_1]

I don't know about that, my petcock never suffered this problem, nor did my wife's old CB350 twin, which used the same (or similar) petcock.

mystic_1

[fmctm1sw]

One of my 350Fs leaks exactly like this, new sels and everything.  Even worse for me though, my carbs will seep it out leaving my garage smelling like gas.  I've taken to pulling the fuel line off and slipping a fuel line with a plugged end on it anytime turn the petcock off.  Nice thread, I'll take a look at my washers...

[Old Scrambler]

If the fuel is leaking from INSIDE the tubes that feed the fuel lines it makes no difference on where the fuel is coming from.....the tank tubes that drain into the petcock......or the leaky screws. I use new screws, a tight O-ring (or a sliced grommet) AND a flat washer (fiber or metal) against the screw head.  I only have to lightly tighten the screw to squish the rubber..........no more leaks.

If the fuel shut-off valve does not thoroughly stop the fuel flow from the tank tubes, its usually the 'biscuit' that has shrunk, been replaced with the wrong unit, or is simiply worn out.  These are the same petcocks that were used on the CL72 and CL77 models except for the location of the tubes to the fuel-lines. All parts are interchangable.

[mycb750k6]

OK thanks Ol' Scrambler. I'll keep working at it. It's just a pain because (1) I have to remove the tank again (carefully), (2) put it on it side in the grass (more dead grass), (3) take the petcock off and replace (more dead grass) and (4) then repeat the entire process. I've sworn to make a petcock testing whizamagagit using water but haven't figured out how to do it and it wouldn't matter anyway if it's the screws. So I have a piece of fuel line between the two outlets as others have but that's stupid to have to do that. Like I said, I'll get it.

[Stev-o]

Click here>>>>

http://forums.sohc4.net/index.php?topic=77445.0;topicseen

[mycb750k6]

What are you trying to say? I'm not following you.

[bryanj]

Ordinary fibre washers are too thin and the wrong OD to do the job; Copper washers are too hard, only easy cure is to buy the expensive Honda part or what i can get in UK is an aluminimum washer with a rubber insert called a "Dowty" washer used on Hydraulic fittings---but they cost as much as the fibres from Honda

[mystic_1]

$6.00:

http://www.yamiya750e.com/index.php?main_page=product_info&cPath=32_80&products_id=268



mystic_1

[paulmac]

Just got a genuine honda petcock from CMS in the netherlands for my 500K1 because mine was leaking from the same area and I could not  work out why. I took a closer look and found on my old petcock that the brass tube was slightly loose in the petcock body so I pulled the tube out stuck some loctite on and hammered it back in. I put it on my spare tank and tested it, no more leaks. So even if it is new check those brass tubes. Cheers.

[mystic_1]

Just got a genuine honda petcock from CMS in the netherlands for my 500K1 because mine was leaking from the same area and I could not  work out why. I took a closer look and found on my old petcock that the brass tube was slightly loose in the petcock body so I pulled the tube out stuck some loctite on and hammered it back in. I put it on my spare tank and tested it, no more leaks. So even if it is new check those brass tubes. Cheers.

Yup, this is why I was asking earlier about the source of the leak.

mystic_1

[JBMorse]

I have less experience with this than others who've already replied, but my guess is that you are simply over tightening the screws that hold the petcock onto the tank.  The OEM washers in there are soft and if you over-torque them, or squish them too much, you'll distort them so that they won't seal. 
My petcock had a drip from the tube even when turned off.  I tried rubber o-rings and they just deteriorated.  I finally brought myself to spend multiple $s on the OEM washers and it didn't leak again.....until I returned from my 10k mile trip this summer, but I'll probably try replacing those washers again to fix it.

[mycb750k6]

Well in my original post I thought I'd said my final attempt was to install a spanking new NOS petcock which meant new screws, new fiber washers, new screen, new everything so I don't think parts are the problem. I think I wasn't tightening the screws enough because (1) I'm weak and (2) this thread seems to suggest that's the area where they leak. Anyway I've done nothing to fix it because of a back flare-up but when that's done torturing me I'm going to either tighten more with the socket head stainless bolts I bought and/or get some O-rings and compress those under a brass or fiber washer as Johnie suggested. I just haven't been able to get to it but I hoping all this good info in this thread has pointed to the crux of the problem and that is fuel leaking past the fiber washers and screw heads for whatever reason and into the petcock body and out the tubes. Is that about right? It's simply a matter of good screws, washers and proper tightening.