Topic: petcock woes

[Midlife750]

The petcock on my 76 CB750 seems to leak in any position.. the problem is I can't figure out which direction is off. The face plate of the petcock is so rusted, you can't see on, off and res. Which is which?  Is it possible to do some sort of "fix" to this problem, aside from replacing the whole thing? This constant flow of gas leads to a constant slow drip at the overflow tubes. Had the carbs off three times now and everything is good.. float level, needle and seat is clear.. what gives? Finally what would be a good base starting point for initial running. I have the pilot jets turned 1 1/2 turns out.... still no go... help!! Summer is almost gone... 

[chrometank]

On my 76 the OFF position is towards the front tire,ON is down and RES is towards the back..undo the two small screws on the face plate and take off the locking ring and fuel tap and you will find the rubber washer with 4 holes.Replace.
cheers

[dusterdude]

my k1 is the same way.

[Midlife750]

Thanks for the tips! I reckon I'll end up trying to make something out of gasket mtl. So.... the long paddle/lever handle points to the front for OFF, straight down for ON, and points to the back for RES?... As for the pilot screws.. how about running them out 1/2 turn (from my base setting of 1 1/2 turns out)  at a time till it runs? Beginning to wonder if it will be on the road this year..

Thanks for the input!

[Buffo]

My pilot screws are turned out so far I forgot how many turns they have. are you sure you are getting fuel from the slow jet?

well some deal with air i guess. my k8 deals in fuel. pilot screws that is.

Don

[Dennis]

Thanks for the tips! I reckon I'll end up trying to make something out of gasket mtl. .....  Beginning to wonder if it will be on the road this year..

I would not bother trying to make that disc from gasket material. For starters it's probably 2.5 to 3 mm thick. It's molded not stamped. I think that it is still available from Honda. A lot easier and more reliable than homemade. (And those who know me, know that I am not one to go directly to the dealer for most supplies!)

[TwoTired]

This constant flow of gas leads to a constant slow drip at the overflow tubes. Had the carbs off three times now and everything is good.. float level, needle and seat is clear.. what gives?

Did you check the stand pipe in carbs bowls for cracks?

Cheers,

[Midlife750]

update... The bowl leakage has seemed to stop.  The pilot screws are out 2.5 turns and it is getting better, I also bottomed out the slides and raised the main idle screw to get it to at least idle and rev a bit.... it still is quite a bit out from where it needs to be. I suppose I'll have to wait till the guy with the mercury sticks stops by again to finalise it. He did complain before about the newer style carbs... Would switching to the older, round top style carbs be a better choice? As for the gasket, I'll give the local Honda dealer a call on monday... maybe it would be better to stop by in person and get the "deer in the headlights" look from the kid behind the counter when I mention this part is for a 1976 CB750F... **LOL***! Thanks for the tips! 

Cheers!, Mike

[Dennis]

update...  As for the gasket, I'll give the local Honda dealer a call on monday... maybe it would be better to stop by in person and get the "deer in the headlights" look from the kid behind the counter when I mention this part is for a 1976 CB750F... **LOL***! Thanks for the tips! 

Cheers!, Mike

Just realized that you have the "F" or F1 whatever you want to call it. If you have the original tank, the petcock is a different style and does not have that packing with the 4 holes (for which I was just about to give you the part number).
The petcock for the F1 tank is 16950-341-671 usually about $70 +. Individual parts don't seem to be available from the parts list which I have. There are two subassemblies available. They are the "strainer set" which is the upper section and the plastic cone 16951-341-671 about $25 and the body set which is the entire remainder of the valve including the body at about $51 (16952-341-671). If you can't get the individual components, just disassemble it and replace the rubber stuff with o-rings that you will have to match up at the counter in some seal house, plumbing supply or bearing shop.
Good luck, it's going to be a pain.

[jtb]

I have been through my original petcock, (77 CB750 F2) a used petcock that I bought, and finally bought a NOS petcock off of ebay.  The NOS petcock solved my problem. 

I read somewhere on the site that you can drill out the rivets that hold the plate on the F style petcocks, make a new 4 hole gasket, and re-mount the plate with sheet metal screws.  It's a great idea, if you can find some sheet rubber thick enough. I got an old inner tube from a trailer tire at the tire store, but it wasn't thick enough.  Martha was about to kick the MOST beautiful F2 out of the garage because of the gas smell, when the NOS petcock came available.  It was expensive, but it was worth it.  My leak was from the body of the petcock, not from the carbs.

So, I am going about 60 mph down the highway earlier tonight, when a 28 year old wire breaks.    You can't win.

John

[Dennis]

The '76 is an F1, no rivets, 2 screws in the plate. I have a '75 F1. That's the way it's shown in the parts books and that's the way it is on the bike. I also found a '76 F1 for a friend, his is that way also.
Apparently a different petcock than the F2. I have no idea what other differences there might be. As I mentioned above those parts are available from Honda. We just bought the strainer set from a local dealer this week!!

[Midlife750]

Thanks for the info to all that responded, and thanks Dennis for clearing up yet another long time question I had... So I now know it is an F1, as the petcock indeed has two screws on the front. Way back when I first got the bike, I took it apart and cleaned out some sludge that looked like orange jelly.... As I recall it was not in the best condition, especially the cone shaped piece with the 2 holes in it. I'll have to get with the local Honda dealer to find these parts. I suppose if I end up being unable to fix it and have to get a different tank, then the seat will have to be changed to suit the new tank? I've heard the seats and tanks are different.

Thanks for your input!
Mike

[vames]

The 75-76 F1 petcock has a cone-shaped plastic valve that turns in a cone-shaped bore in the petcock body to let various holes line up. No rubber pieces. Mine leaked in all positions, so I took it apart and found varnish built up on the plastic cone and in the bore it turns in. Cleaned them both by going over very very lightly with really high grit sand paper. (rolled the paper into a cone shape to get it in the bore). Rubbed some grease on the pieces them and put it back together (have to make sure that the cone is in the right position since it can be 180-degrees off if you do it wrong - you can see if you did it right after you put it together by blowing through the gas intakes and moving it to different positons). Cost: $0. Works perfectly.

[Dennis]

Mike,
You might want to take a look at that "strainer set" I mentioned above. If I had realized what was included (didn't have the parts list at the time) I woud have purchased that for my bike rather than the used fleabay petcock that I bought. As I mentioned it includes the fuel pick up with the nylon sock (that's the strainer I guess) the rubber gasket and o-ring that go up top and the plastic cone. That should take care of a leaky petcock unless something is broken. You should be OK with that unless the tank is really bad. If the tank is sound but still rusty or dirty, you can always clean and seal it, just don't use "KREEME".