Fuel Delivery Problem - Tank to Carb Fuel Rail

Hello again everyone,

Made some progress yesterday, Removed cone filters - (surprise surprise) and was able to get the bike started 82 KZ 750 LTD 4.

I sprayed some carb cleaner in without any air filter setup and the bike seemed to run on all four cylinders and sounded good. So I then bypassed the tank, petcokc, filter, and ran a waterbottle with gas in it and a vacuum line in it to the hose that plugs into the carb rail in the middle of the carbs
Rail: [ ] [} I [ ] [ ]

Started up and seemed fine. When I turn the petcock it seems that it doesn't make a difference as it is stuck open. I see that some people rebuild it and some replace it. I was thinking of putting a manual valve in:

www.amazon.com/gp/product/B0018U234W/ref...&smid=A2KDF402UD3HTO

and use this filter as the one I have currently is pretty small and gets junked up pretty quick as I have a ton of rust in the tank.

www.amazon.com/gp/product/B01DMWT8NC/ref...&smid=A1CP71A0ML4NK8

This bike will only be used for commuting maybe 15 miles each way morning and night so 30 miles a day so I don't mind cleaning the fuel filter every weekend or so.

Just looking for advice to see if I need to replace petcock, i'm already over budget and would like to get running sooner then later. I have been looking for a replacement tank and am down to use something else but has not come up yet.

Thanks for reading and any advice you guys have, excited to almost be there.

With engine running, vacuum petcock is supposed to allow fuel flow in any position.

Good Fortune!

Thanks for the response Patton, The petcock has fuel flow out of it when the tank is out of the bike and in the bike but off from any position of the petcock. The line coming from Carb 1 that goes to the smaller port on the petcock did have fuel in it when I got the bike and since then it does not. I thought I read somewhere that it was a fuel overflow but that seems wrong, seems to be a vacuum port then to start the siphoning?

Thanks,

The smaller port on a vacuum operated petcock is for a vacuum hose from the carb which supplies vacuum to the petcock when the engine is running. Which is supposed to allow fuel flow in ON or RES positions of the petcock when vacuum is being supplied (engine running). When the engine isn't running, a vacuum operated petcock is not supposed to allow fuel flow in ON or RES positions of the petcock.

The PRI position of a vacuum petcock is supposed to always allow fuel flow from the petcock, with or without any vacuum being supplied to the petcock.

At carb end of the vacuum hose, the hose will attach to either a dedicated vacuum nipple on one of the carbs or to a sync nipples on one of the carb holders.

The vacuum hose should not have any fuel in it. Fuel may enter the vacuum hose from a malfunctioning vacuum petcock due to dirt or crud inside the petcock or due to damaged part or parts inside the petcock (such as a damaged diaphragm).

If the vacuum petcock is malfunctioning, the petcock may sometimes be restored to serviceable condition by disassembly and cleaning, and perhaps installing a petcock repair kit which includes a new rubber diaphragm and hopefully a new o'ring and spring. If more than cleaning is required, I believe Z1 Enterprises carries the repair kits.

Good Fortune!

This link includes a downloadable service manual
Click here > mbsween.bike-night.com/kz750l3/index.html
Then scroll down to and click on "The Bible" which will download the FSM.
See page 43 and page 149 for the fuel tap (aka petcock) information, disassembly, diagrams, etc.

Good Fortune!