swapping to gravity fed petcock 81 kz650 & master cyl. rebuild kits?

my 81 KZ650 H1 has been quite the project and still is. i have cleaned the carbs several times and completely dissembled and reassembled them once to try to fix the leaky fuel rails. with the petcock it hadn't leaked until now. when i remove my tank it'll just drip out a tiny bit which at first i thought was just some left in the tube dripping out but upon further inspection i noticed if i sloshed the gas a little bit it would push little bits out. so i took the petcock apart to see the condition of the inside. the diaphragms seemed intact, no tears, not "bubbled" or anything like that but i did notice lots of lime buildup on the spout that seals being pushed by the spring and has an o-ring at the top. i cleaned it up and VERY slightly stretched the spring to give it a little more push. then when looking at the manual i realized the tube that is supposed to be on the top of the petcock is missing. i think the tube is what determines what petcock option to be on (ON or RES). would this tube missing cause this issue, is it crucial to have it? i didnt see the tube in the tank at all, and the last time i took the petcock off was when i got the bike a year ago in non running condition so i dont remember if it had one or not and i didnt know anything about it at all then so i wasnt sure how everything went together so i wouldnt have taken it off if it was on there. i guess the main question of this post is would it be worth getting a gravity fed on/off petcock or should i try to get the parts for the vacuum one? i may just go out and see if i can find it anywhere in the tank again. also i have been trying to figure out why my front brake has been getting soft and no fluid in the master cylinder well i just realized that the master cylinder is leaking. it's coming down the brake handle but when i come out from work ill notice break fluid has dripped down to the ground and some on the forks. (i clean the dripping every time and refill it when its low)but the master cylinder is dirty and ive only cleaned the reservoir out. ive read that these are notorious for leaking and requiring a rebuild just wondering if anyone has gotten a kit, if so if there is one better than others, cheaper than others, so on & so forth. or if these can be repaired without a full kit. thank you all!
EDIT: I leftout another issue, when i park the bike if i put it on the side kickstand gas drips from #2 carb area. i have only actually seen it drip from the tip of a float bowl screw but i know they are all tight and its not the gasket. all 4 carbs do have some yellow goop build up which is from the gas evaporating. there is no dripping from the other carbs just #2 area which i have bypassed the accelerator pump because it is hard to find the covers that were missing. if i put it on the middle kickstand it has no issues with dripping. i have set the float heights to 23mm well converted it to .9 in and set it to that. now when i did it, the manual doesnt show a very clear picture but it says it is measured from the mating surface so i dont know if that means actually in the area the float bowl sits in or just outside that area on the raised part. either way, if it is set on the inside part i still have it set a little low than its supposed to which would mean that if i set it any higher i would imagine the leaking would be worse. sorry i know explaining things without pictures is very difficult. let me know exactly what to take pictures of to help you understand what im saying! i will attempt to get pictures explaining this.

If the brass tube in the petcock is missing you are always in "Res" mode" at "On" Position.
Dripping fuel out of the carb bowel on the side stand is an leaking bowl gasket sign if the float bowl high set right.

I prefer a new set of carb bowl gaskets for your carb set, they have to be replaced after four decades!!!
Here some links:

www.motorradbay.de/z650b-yfcg-27r_1-gask...54a1dbed8fd604eadfdb
www.motorradbay.de/z650b-yfcg-27_1-gaske...54a1dbed8fd604eadfdb
www.motorradbay.de/kz650h-yfcg-37_17-gas...54a1dbed8fd604eadfdb

Some master cyl. rebuild kits

Single disk
z-fever.de/shop/product_info.php?info=p1...onsize-14x52mm-.html

Dual disk
z-fever.de/shop/product_info.php?info=p1...ze-15-8x62-7mm-.html

Fr brake master cylinder. I didn't read the topic post. hee. I don't think a piston kit is available for the KZ650-CSR. Although I haven't verified this, the 78 KZ650-B2 piston assy might could be used. The piston bore should be the same as the other piston parts are the same. If the piston doesn't fit right, you might be able to swap the rubber seals. see pics for comparison.

...1981 KZ650-H1. 43020-1027. Used & missing a seal. ..... NOS piston>> imgur.com/QFR4NJU


...1978 KZ650-B2. 43020-1026. photo from Z1Enterprises.com. not sure if they still have the piston assy.

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Just a thought, but perhaps source a front master cylinder from a different make and model bike? I see it done for other old bikes. There's a number of newer bikes out there with regular handlebars now, that are cable clutch and master cylinder equipped, and may be great donor candidates. At the least, you'd no longer have to deal with obsoleted rebuild kits for the master cyclinder either.

If the stock handlebars have been changed or you plan to do so, then a modern master cylinder is a very good option. I'll suggest one from a Honda CBR500R. It's small w a silver brake lever & should fit good with superbike bars or any other low handlebars & has a mirror orifice. The stock m/c will be at an angle with low handlebars & can be a tight fit.

Basic criteria: 7/8" bars. mount angle. single disk piston bore (1/2" or 12.5mm). mirror orifice. you can use the old brake light wires & splice terminal pins in place of the switch. or fab a new br light wire harness. very easy as it's just 2 wires from the headlight bucket to the m/c.

Manual fuel valve. the 81 650-CSR should have 34mm bolt hole spacing. EB seller = custom-moto-pro. Made in USA?
EB search = Yamaha Raptor fuel valve or fuel cock. good prices & Made in Japan.
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I will look around to see if any buddy's have a m/c laying around. For the leaking, I noticed that after sitting for a while Itll run rough until I sit on it and hold it upright. Not too bad but still noticable. Is it just the fuel being on one side of the carb bowls? A friend suggested maybe i could keep everything petcock wise just put in an inline shut off is this recommended? I looked around inside my tank and found this plastic filter was tucked in a corner eventually with shaking the tank I got it out is this what was missing?

No eBay APP ID and/or Cert ID defined in Kunena configurationThat isn't the stock petcock filter screen. It should be oblong shaped & should fit into or cover both holes. Similar to this one.
note: the 51023-1375 petcock should be 44m, so it won't fit the 81 650-CSR which is 34mm.

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The screen on your petcock appears to be from a different model bike, and there should be 2 screens – one for each fuel port in the petcock. Early KZ650 petcocks had those screens, but the early petcocks were manual not vacuum actuated, so if your petcock has a vacuum port it is not the early type.

The picture below shows the petcock and screens that were supplied on the 1977 KZ650 manual petcocks. Notice that one screen sits on a brass pipe. That brass pipe attaches to the petcock fuel port that is used when the petcock is in the normal run position. That brass pipe prevents fuel near the bottom of the tank from flowing from the tank when the petcock is in the normal position. Notice the other screen sits down lower right on the petcock casting. That screen is attached to the reserve fuel port in the petcock. When you run out of fuel with the petcock in the normal run position, which draws fuel through the brass pipe, you turn the petcock handle to reserve. Doing that causes fuel to be drawn through the fuel port that has no brass pipe, and that lets the fuel below the top of the brass pipe to be used. That fuel below the top of the brass pipe is the reserve fuel.

The photo of your petcock does not show a brass tube. Instead, it shows the one filter sitting right on the petcock casting and the other filter missing. Without the brass tube I see no possible way for your petcock to provide a reserve amount of fuel. To me it looks like someone has fiddled with your petcock and may have ruined it. If your petcock does not have the brass “reserve” tube I would replace the petcock with a new one. Ed

Thank you! Are there any good replacements for the kz? I'll look on eBay when I get time

From a reply above that also has info for an alternate Fr br master cylinder:

Manual fuel valve. the 81 650-CSR should have 34mm bolt hole spacing. EB seller = custom-moto-pro. Made in USA?
EB search = Yamaha Raptor fuel valve or fuel cock. good prices & Made in Japan.

Whatever fuel valve seems right, be sure to verify the bolt-hole spacing.

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