fuel supply

ok ive got a 1976 kz900A. just purchased recently and did a lot of work ot it. i replaced the intake manifolds, fuel filters, cleaned the gas tank, cleaned the carbs and replaced the carb top and bowl gaskets, checked and adjusted the valves, installed dyna S ignition, replaced the spark plugs, and replaced the petcock. it runs pretty good when it runs but sometimes it dies. i found that i wasnt getting good flow of gas to my carbs. so i pulled the lines off my petcock and with it in the on position it would not flow continuously. so i took it off and blew it out. then it flowed continuously. when i put lines back on it still seamed like it wasnt flowing well. so i blew compressed air through the vents on the carb bodies. as soon as i did that the gas started flowing fine and i didnt have any trouble. that was yesterday. now today the same thing happened. so i blew compressed air through the vent and the gas started flowing. any one ever experience this before?

Might be crud in fuel tank clogging the petcock pick-up tubes inside the tank. The air pressure might be temporarily clearing the clog and then the crud settles back down around the pick-up tubes.

Suggest removing petcock and cleaning the pick-up tubes. Would also flush out the fuel tank to remove any grit, dirt, etc. suspended in the fuel.

Test by running line from petcock to a container and allowing fuel to run from the tank and keep running until you're sure its all clear.

i cleaned the tank twice with phosphoric acid. the inside is pretty clean. probably a little junk in there but not enough to clog the petcock. i removed the petcock yesterday and blew it out. the filters looked brand new still. i just replaced it. all the fuel coming from the petcock is clear. could the fuel tank vent cause this? ill have to try it with the tank open.

Hmmm...carbs or tank not vented properly?:whistle:

Seem to recall reading sometime ago where someone had connected the carb air vent nipples to each other with a single piece of hose. Which of course defeats the purpose. Just being sure that's not the case in this instance.

New from the showroom, each vent nipple has it's own hose running to underneath the seat.

The carb bowls need to be vented AND the tank needs to be vented. Your bowls vent via the brass fittings located in the center inside of the #2 and #4 carb bodies. They cross connect with the #1 and #3 carb bodies via the short black hoses which join the vent passageways for the carb pairs. Make sure the vents are NOT obstructed. Try running the bike with no vent tubes or connections. If the tank isn't vented (which sounds more likely in this case), then try opening the gas cap and running the bike. If this solves the problem, you will need to rebuild your gas cap or replace it as that is where the tank vents.