Hi, so sometimes when I turn off the engine in my 1973 240z, it rattles and hisses for a few seconds after I remove the key and all around doesn't sound good. It doesn't do it all the time, but its starting to worry me. Does anybody know whats wrong? Thanks! Oh, and its a 1973 240z runnning an l28 with flattop carbs.

Research engine dieseling or run-on. Could be a few things like excessive carbon deposits or engine overheating, for example. I'd check your coolant first and flush it if it hasn't been done in a long time.

I think you will find that those flattop emission carbs are the least desirable carb you can run. Replace with round top S.U.s from a 72 and burn premium fuel.

Here's a video of a 260Z with a horrible case of run-on.

Yoshi.......An L28 with flat-tops? That's a first......very rare! Bruce Palmer where are you? I agree with Dobber.

It's a 73 with a 280Z engine but has the stock 73 intake setup....

When I bought my car it came with an l28 but retained the flattop carbs from the 1973 year my car was made (1973 240z).

Edited February 2, 201114 yr by sblake01

I've heard that run-on can be caused by too much advance......try retarding your timing. See if that helps.

Thanks guys for all the help so far! and I am pretty sure it kept the flattops due to the carbs being the stock intake setup. I would like to replace them eventually, but I doubt thats the problem, beyond the butterfly valve not closing all the way. I will try to adjust the timing as soon as I can get a hold of a timing gun. New development though, as I was driving today the engine just started to cut out and when the engine did cut back in, there was no power at all. Are these two problems related, like would this new problem also be caused by bad timing? Thank you everyone so much so far!

Yoshi.......An L28 with flat-tops? That's a first......very rare! Bruce Palmer where are you? I agree with Dobber.

OT: Wow your dad's cars are wonderful!

Related to this topic: I have 72 240z and its having the same symptoms. Banging, rattling and hissing after shutdown. In my case the engine is overheating..There is either air in the system or bad head gasket?

Yoshi......Just loosen the 10 mm nut on the base of the distributor.....start the car then twist the distributor counter clockwise a small amount.....see if that helps.Timing can be set by listening to the engine to find it" s smoothest idle.Make sure the engine is fully warmed up when doing this.Good Luck.

Engine run-on can be a symptom of overheating, at least cars that are running way to hot will run-on.