My 240z has been the most reliable car that I've owned for years......until yesterday. Took it out for a drive and it ran great as usual. Stopped at the local c-store for an energy drink, fired up the car, and it had almost no power at all (had to limp it home). When trying to accelerate, the car would crawl to 3,000 rpm and then begin backfiring through the exhaust. At idle, it stumbles around 400-500 rpm, then dies. My question is this: I want to know where to start trouble-shooting. Are these symptoms more represenatative of a fuel system issue or an ignition issue?

Any suggestions that you may have would be greatly apreciated. By the way, it is a 1970 240z in mechanically stock configuration with SU carbs and stock ignition system.

Thanks,

Mike

Sounds like an ignition problem to me. I'd suggest to check your timing first, and confirm your spark plug wires are all connected properly. The fact that it was backfiring through the exhaust tells me that the engine was getting fuel, it just wasn't combusting until it was out in the hot exhaust pipe. I recently ran into an issue with my vacuum advance failing which caused timing problems. Other things to check will be your points, rotor, and distributor cap. Best of luck!

Thanks, Jarvo. I will start with the points, rotor, and distributor cap. I know that the wires all connected correctly. Is there a way to troubleshoot the vacuum advance?

Mike

You can pull the distributor cap off, and then pull the vacuum advance hose off of the front carb. Suck on the hose & look for the breaker plate within the distributor to move. Also, if when you 'suck' the vacuum should hold. If it doesn't then the diaphragm inside is shot.

Does anyone else have any opinions/thoughts on the question of whether I likely have a fuel problem or ignition problem? (I always get second opinions from my doctor even if he just diagnosed a common cold:)

Thanks again, Jarvo, for the vacuum advance troubleshoot technique. I just hope that I can find a replacement unit should mine turn out to be defective.

Mike

2nd opinion: ignition.

Look at your plugs too,

Thanks for the second opinion, Blue. Technically, it's a third opinion, as the ignition is what I originally suspected. However, a neighbor of mine who has forgotten more about old school cars than I'll ever learn, was convinced that my problem was one of a fuel issue. Perhaps I'm not quite as mechanically-challenged as I thought I was:)

Having said that, diagnosing is one thing......fixing the problem could be a different story altogether. Will proceed with checking the points, plugs, cap, rotor, wires, vacuum advance, and timing and see where it goes from there. Thanks again to you and jarvo.

Mike

4th opinion:

Ignition, though if after checking the cheap and easy and not solving the problem, I'd check the cheap and easy fuel supply side. If still no satisfaction, I'd take a deeper look at the ignition side.

Your symptoms sound awfully similar to ones I had when I installed what proved to be a dying vacuum advance pulled at the junk yard. Pull the hose, plug it and see what happens. You'll feel a little down on power, but if the misfiring stops, the vacuum advance was the problem.

Chris

5th opinion- ignition

Check everything for tightness- plug wires, wire leads

Check the cap for cracks

Look at your points- you might have lost a contact pad

Check for a big vacuum leak also

Check fuel filter for clogging

Opinion 6. Fuel--- I once had a car that was sucking debris onto the fuel pickup in the tank.

When the engine was shut off the debris would drop off, allowing the engine to start again till it happened next time.

This was not a Zed by the way, but an old English car.

Also water in the gas can cause all sorts of weird running. Same old car!!! I poured some methylated spirits in the tank, and it was supposed to mix with the water

and flush it through, which it eventually did.

Edited September 20, 201212 yr by olzed

Advance Mechanism Roller Bearings INSIDE the distributor and below the points plate.

When you suck on the Advance Diaphragm tube, look at the points plate and note the travel action.

Is it smooth in and out with little or no hesitation?

Does it take a small amount of vacuum to actuate?

When you release it does it spring back or just sit there?

Any of these answered as NO point to that plate.

There are some ball bearings imbeded in the plastic "feet" below the plate. When they get coroded they can stick in the plastic and not roll. They can also break out of the plastic cup and just be rolling around in the bottom part of the dizzy.

Before you start replacing other items, check this as it's the easiest of them all.

FWIW

E