So i just got a 240z last week, always loved them now finally a chance to own one. i have been doing very well fixing her up but one thing has me stumped. When the car is running the carbs both appear to work fine, but once the engine is shut off, the front carb begins to pour out fuel from the opening where the air filter would normally go, this continues for a good 15 to 30 seconds after the engine is shut off. any ideas???

Im assuming origional carbs and engine.

What type of fuel pump.Does it still have the fuel return line which leaks excess fuel back to the tank? Might be a leaky float valve in the carb or float level set wrong.

Edited September 30, 201014 yr by olzed

I'm betting money on the incorrect float setting - just a warning - before you start with the float adjustment - read and research - also go ahead a purchase a min of 4 float bowl gaskets from your local Nissan dealer or Z Therapy - trust me, you'll need them!

I had a float bowl needle valve stick open and it leaked while the car was running. I was lucky it didn't burn the car up.

My money is on a stuck float valve.

Sometimes you can unstick the float valve by tapping the float bowl with something like a screwdriver handle. If that gives no results, then you probably need to get into the float bowl, remove the valve and make sure it's clean and working (blow compressed air through it). And while you're in there, you might as well make sure the float is set properly.

Man, that's a stumper. Hard to imagine that with only 3+psi fuel pressure that there would be enough residual pressure, after shut off, to overfill the floatbowl enough to run out the mouth of the carb.

You are new to the car, right? First thing I'd do is to look into what's there in the way of fuel pump/s. Assuming it's a 240 there should be a mechanical pump on the side of the head and there may be an electric pump back by the tank. Sum total output should not exceed like 3+ psi.

Let us know what you find. And do not assume the previous owner/s played by the rules.

Yes, listen to Bruce.

I've heard he knows a 'little' bit about carbs.

Sounds like both a stuck valve AND something causing overpressure like an over-pressured electric fuel pump or clogged return line or boiling fuel.

Fuel 'pouring' out for 15-30 seconds seems a little extreme.

Checking the float valve is something you should do if you decide to open her up. But also the float itself has a seam around it and eventually that seam begins to take on fuel and no adjustment will cure the problem. Get a rebuild kit from Z-Therapy or any other supplier and also look into getting some replaacement GROSE JETS. If you are going to open it up you might as well set your mind at ease with a complete service. The kit should come with a guage to porperly set the float height as well. Also look at an exploded view of the carbs.

Shouldn't the grose jets (float valves) be changed in pairs? I suggest looking at both carbs. Once you see how easy it is to set the front, you'll see that it's worth the effort to check the rear.

I thought they quit making the Grose jets for a number of years, did they just start making them again? I am excited they are available again and will order some immediately!

We have not been able to get Grose Jets for about 8 years.