Topic: 750 K4 Petcock

[JeffK]

Guys, I had a thread on here last week telling a story of how I left my gas on and gas filled the crankcase. Turns out I did not leave the gas on. My petcock leaks. I bought this Petcock off the internet (it was a cheap one).

So now I have one old petcock and one new petcock. Both leak in the same exact way. They both dribble about a drop every five second out the nipple on the left.

I am assuming I bought a cheap petcock and I got what I paid for. Can any of you drop any wisdom on me about this? Do I buy a new one again? If so, what kind is a sure thing? Do I rebuild the original? Can you successfully rebuild one?

Thanks for the help guys,

Jeff

[bryanj]

Did you fit new washers under the heads of the retaining screws as if they leak gas bypasses the on off bit

[69cb750]

I am assuming I bought a cheap petcock and I got what I paid for.

That's the way it usually works.
Honda makes high quality parts, if you want good parts buy oem parts.

[Bodi]

There are two types of petcock valve, a cone type and a flat plate type. Easy to tell apart, the cone shaped housing gives that type away.
Probably you have the flat plate model. There's a cover plate with two screws or "rivet" things holding it down. Drill off the "rivet" heads if it has those, unscrew the screws if it has screws. The lever part and a serpentine spring will come out, underneath is a rubber disk part with 4 holes: one is on a keying pin, one goes to the hose nipples, one goes to the "on" inlet tube, last goes to the reserve inlet.
To renovate, check the rubber disk for wear. There are (were?) slightly raised rings around the holes, if worn to flat the disk is not too good anymore. Some are reversible so you can flip it and get a virgin surface. They are available on ebay and such as replacement parts but I don't think Honda ever sold them separately.
The lever part is pretty much flat except for fuel channels, these line up with the rubber disk holes to let fuel flow from tank to nipples.
Polishing (lapping, really) the surface flat and smooth helps a lot. Just some metal polish on a flat plate (Solvol is excellent) will shine and flatten the surface.  I have seen badly corroded ones on bikes left years outside, this is probably unrepairable.
With needlenose pliers, make the spring bends higher for more tension.
Lube the friction areas with whatever lube you like, I use Dow 111 silicon o-ring lube for that kind of thing.

If you drilled off the "rivet" heads: these are obviously not rivets, just peened over teats in the housing. Get a 4-40 tap drill and tap and two round head 4-40 screws, - stainless is good, brass is not good as electrochemical corrosion will attack them. Drill straight through the case using the first drill mark as a centre to align the drill. Tap all the way through: use some lube (tapping fluid, WD40, 3 in 1, whatever you have). The metal is super easy to tap but be careful not to snap the tap off: 4-40 taps are quite delicate.
Clean the case and blow out the holes. Reassemble with lube. Use a bit of antiseize on even SS screws.
It should turn much smoother and not leak.

The cone type is totally different except for the cover screws. Not much can be done to revive a really worn out one, a bit more tension on the spring plus careful cleaning - particularly the bore and plastic valving cone - and adding some lube may stop any leakage. It has for me anyway. Reassembly is trickier - the valving cone has to be keyed correctly to the lever - but it isn't rocket surgery.

[ekpent]

Did you fit new washers under the heads of the retaining screws as if they leak gas bypasses the on off bit

+1 On what Bryon said. I fixed a petcock leak on one of my last project 750 bikes by just replacing those two fiber washers under the screw heads. Definitely put those on the list. I found some at an Ace Hardware that worked though they were black and not the Honda red/orange color.
 Another leak source for a K4 is the 4 holes rubber gasket that sits behind the tap handle. Edges around the holes get worn down/rubber gets old.

[JeffK]

Guys, I read all your helpful replies and I decided to open up the new petcock and check it out. The 4-hole rubber washer was all screwed up in the hole (see pic below). I took it out and it was indeed reversible so I turned it over, reassembled and now it is not leaking (on the bench) at all. I think I may have solved this one.

BTW - I put some vaseline on the face of the 4-hole washer per a suggestion above to avoid that issue in the future.

Thanks everyone,

Jeff

[HondaMan]

Guys, I read all your helpful replies and I decided to open up the new petcock and check it out. The 4-hole rubber washer was all screwed up in the hole (see pic below). I took it out and it was indeed reversible so I turned it over, reassembled and now it is not leaking (on the bench) at all. I think I may have solved this one.

BTW - I put some vaseline on the face of the 4-hole washer per a suggestion above to avoid that issue in the future.

Thanks everyone,

Jeff

This often happens over time when the petcock is not frequently operated. The face of the rubber dries out and sticks to the lever-valve face, and then when it finally gets turned it distorts the face of it, time after time, until it leaks. This seal is available from Honda: I suggest using theirs as I have recently suffered several aftermarket ones that were not as thick as they should be, so they leak...