Hi all. I'm trying to tune my carbs and it appears that when ever my engine idles low (about 1200) large bubbles form in the fuel filter. When I shut the engine off the fuel filter loses all prime and the gasoline drains out. Needless to say it is tough to start with a huge pocket of air in the lines and the idle dies around 1100. I replaced the lines about a month ago, cleaned out the gas tank and replaced the filter. Does anybody know what is causing the problem?

Sounds like a bad diaphram in the mechanical pump causing the leak down. My fuel filter never fills full even at high rpms, mine is before the mechanical pump.

I'll take a look. How can I fix that? Would I need to replace the whole pump?

Sorry, yep a new pump is the only way to fix a bad diaphram....

you can install a electric pump. Your car is wired for one. A great mod. is to install a fuel pump from a RX-7 . Just be sure that it is from one that is carberated and NOT injected. They will give all t he volume that any carb, set up can use period and the pressure is low but fine for the SUs. I have been using one for two years and it works great. $15.00 at the bone yard. No vapor lock either. Check your oil because if the diafram is blown it could be pumping gas into the crankcase. NOT GOOD

I don't think you have a fuel / pump problem.My Z has done that same thing forever.So does my '46 chevy truck with mech.pump.I can turn off my Z and within a very short time remove the fuel filter with little fuel loss.Hit the switch and its full (with the standard air bubble)in seconds.The carb bowls hold enough fuel to compensate for the moment of air is my guess.If mine sits for a month or so I have to crank it a little more.Once it starts I just bump the starter to crank it any time hot or cold.I can leave it overnight,over a weekend whatever it cranks up fast.Its just a month or more then its crank for about 6 seconds,Stop and put my seatbelt on.Crank for 6 seconds.Stop and put my windows down.Turn the key Vroooom!!

A couple of things. I "fixed" whatever the problem was. I guess the fuel filter just doesn't fill up all the way when the car is on. However there was still the matter of the large bubbles that were forming and the loss of pressure when I shut the engine off. I opened up the fuel pump and everything looked fine untill I looked at the rocker arm. There was about a quarter of an inched of crud between the rocker arm and the hing. After this was removed the pump worked fine and the low idle bubbles disappeared. Over all I'm very happy. Thanks guys.

Nice play on words, CHAOTIC Z

Rick.