Petcock Replacement for a '76 KZ750

Hi all,

long time, no post. but 'tis the season.

i've got leaky carbs (if the bike sits on it's side-stand over night with the petcock turned to off, i get a small (but significant) pool of gas under the bike.) if i shake the bike side to side a bit, a good little amount of gas comes out the overflow but eventually stops. this leaking doesn't occur with the bike running.

my theory:

1.) from my readings in the archive, leaving your bike on a side stand (center stand was ripped off before i got the bike) you should expect some overflow of gas. ok.

2.) i believe my petcock doesn't work at all. it's just an "always on" petcock now. (this is from previous observations.)

do these two things together sound like a reasonable explanation for the small pool?


my solution:

replace the petcock and see if that takes care of it.

can anyone recommend a replacement petcock for a 76 KZ750? Z1 doesn't seem to have too many options for dual-output screw-in ones.

Thanks As Usual Guys/Gals!

mind2find wrote:

...1.) from my readings in the archive, leaving your bike on a side stand (center stand was ripped off before i got the bike) you should expect some overflow of gas. ok.

2.) i believe my petcock doesn't work at all. it's just an "always on" petcock now. (this is from previous observations.)

............

my solution:

replace the petcock and see if that takes care of it.

can anyone recommend a replacement petcock for a 76 KZ750? Z1 doesn't seem to have too many options for dual-output screw-in ones.

I leave my bike on the sidestand quite a lot. I've not had this problem.
How much do you "shake" it side-to-side? Violently?

Looks like you have a petcock problem like you said. First, your petcock, is kinda' rare, but many from earlier z1's can be used as replacements. But forget that for now. Instead of getting a petcock as a first step, why not get the few-dollar petcock rebuild kit? Our petcocks come off easily, come apart easily, and can be cleaned easily and replace the o-rings (the "kit" is basically 4 o-rings).

I have 3 petcocks for the 750 twin (I keep a spare) and all were cleaned this year with rebuild kits. Now they work perfectly, and they were not good before.

Give it a try. And once you get used to turning the petcock off, maybe all the other problems will go away...

welp, that was one thing i forgot to mention. i did "rebuild" it, which seems like an excessive term as far as 4 piece petcocks, but anyway, i replaced the filter, rubber washer, o-rings, etc.

i guess i might do good to just drain the gas and pull it apart again. see if i didn't XXXX it up somehow. although i seem to remember realizing there was really only one way to put the darn thing together again so i don't feel like it's my fault.

(just as a question, i couldn't put a suction valve on this tank, could i? with two outputs?) frankly, i don't even know if those exist or what would prevent me from being able to put on on my bike.

thanks for the help!

oh, and would this (unfortunately priced) petcock work by your (Z1) calculations?

www.z1enterprises.com/detail.aspx?ID=28

Oh, and you just have to wag the bike back and forth and the gas dribbles out of the overflow outlets.

So here's part of my confusion on this one. The service manual doesn't even list the individual ports on my carbs. I've numbered them here.

1. is what I thought were the overflow valves (hence the tubing) but are they, uh, vacuum valves? ones that Don't need tubes all the time?

2. is where the gas is leaking out after sitting for a while and then rocking the bike. let me guess... overflow valves that i should have tubes on?



crack the mystery kz'ers!!

Post edited by: mind2find, at: 2007/05/04 22:56

mind2find wrote:

...

Yep, the #2 are overflow from the float bowl area. The fact that you are getting fuel out of them means something is wrong. That over flow is at a pretty high spot, so your floats are not working properly for some reason. It could be that they are adjusted wrong, it could be that they have functionally failed (common with age), it could be that they are gummed up or covered in crud, etc.

On another note, I noticed a couple other things in your pic, and thought I'd give you a couple tips:

Get new filters - there are filters with brass elements that filter better than those screen ones. You can get them for about a buck or two each at any bike shop. Change them every year, or at every oil change if your tank it really rusty.

Route your fuel lines the other way round - run the line that comes off the rear-facing petcock outlet over to the right carb. Route the one that faces to the right, over to the left carb. This may sound crazy, but it actually works perfect, and gives you more room to hide the filters and everything underneath.

Use a better fuel line! The stuff your using looks pretty stressed and thin. I use the GoodYear stuff I get from AutoZone.

If you *do* use the GoodYear, fueline, little brass-element filters, and route them the way I mention above, then you can use this info:

Cut it into pieces like this:
For the line to the left carb: Piece A is 9" (can be longer), and connects to the right-facing petcock port, crossing the engine in front of the throttle cables, over the right carb and back toward the left. Fuel filter connects to Piece A and should be about 1" of exposed filter. Piece B is 4" (can be slightly longer) and connects the to the fuel filter and to the left carb.
For the line to the right carb: Piece C is 8" (should not be longer, infact should be about 7 1/2" or less) and connect to the rear-facing petcock port. It continues behind the left carb toward the rear of the engine compartment, where it connects to the fuel filter. Piece D is 2" and connects from the fuel filter to the carb.
In summary:
L: Petcock -> 9" -> Filter -> 4" -> Carb
R: Petcock -> 7 1/2" -> Filter -> 2" -> Carb

Bique,

Big thanks!

#1 I'm assuming that even if the petcock has failed completely (I believe it has) the floats should still be preventing that spillage.

#2 New filters it is. Hopefully ones with a lower profile.

#3 I did have trouble getting that tubing on. Glad to hear a recommendation for another kind.

#4 I'm SO glad for the recommendation of the new line routing. That has bothered me ever since and is something that would have been caught and yanked by accident eventually. Plus it was just plain ugly.

This is why I love this board. :laugh: :silly: :lol:

mind2find wrote:

#1 ...even if the petcock has failed completely... the floats should still be preventing that spillage.

#2 New filters it is. Hopefully ones with a lower profile.

#3...a recommendation for another kind.

#1 Yes, the floats do their best. With a perfect seal, they pretty much do stop any excess from the petcock, but over time, it can still seep through in reality...

#2 The filters I get (from z1enterprises.com) are only 1" long of exposed surface once in the hoses

#3 I went and checked - the stuff I get is: GoodYear Fuel Line Hose and Emission Control Hose, 1/4" x 24", part # 65122... and if you use the lengths I described in the previous post, you will use almost exactly the 24"

#4 Glad to help. I recorded all those lengths for my own benefit, never thought anyone else would need it...

A quick check on testing my float level. Can I run water through these guys so I don't have to put them back on the bike to test if I got the float level right?

The service manual is very vague about how to adjust the tang so I modified it a small bit to close the valves a bit sooner.

Does testing them off the bike sound like a kosher idea? Just trying to save time. :S

mind2find wrote:

A quick check on testing my float level. Can I run water through these guys so I don't have to put them back on the bike to test if I got the float level right?

The service manual is very vague about how to adjust the tang so I modified it a small bit to close the valves a bit sooner.

Does testing them off the bike sound like a kosher idea? Just trying to save time. :S

It's a great idea to test them off the bike. You probably should test them a final time once back on the bike to be sure though.

I wouldn't go guessing about the floats though. Don't adjust them unless your measurements tell you to!

Water? I don't know. Believe it or not, I never thought of it...

Timely thread...I just dug my 750B out of mothballs, installed NOS tank, tail seat, chain guard, covers, and assorted rubber bits. I even rebuilt the petcock! I put in a new battery, tried to fire it up and the gas came gushing out of the overflow tubes! It looks like I'll be pulling the carbs to check out why the floats are sticking. I might as well install the filters and re-route the fuel line why I'm at it.

Post edited by: macattak, at: 2007/05/19 22:33

Gee whiz, is *everyone* working on their 750 twin carbs today? I just did the float adjustment this afternoon, using Steell's inverted method - seems to have works great. Nice not to have to check, remove, bend, put on, check, etc. That story is here

Biquetoast - that is an interesting idea on the line routing. I despise the way mine look, though I know the filters I am using are too freakin' long. I need to go over to Z1 and get some of those button jobs. Hmmm... I need a clutch lever too....

Great stuff on this board!