I have a 74 260 that will start and run great for about a half hour then it will start sounding like its on 5 cylinders, after it sits for awhile it fires right up and goes great again for about half hour,then all over again.. Does anybody know what is happening, im very frustrated.. It has the original flat top carbs.

I'm guessing this is an ignition issue. Start by checking out the plug wires for shorts (best done at night). replace as necessary. Also, check out the distributor cap for cracks. Arcing can occur due to cracks or carbon traces on the inside of the cap. If traces are evident, clean the cap and try again. If cracked, replace it. Another source could be a bad coil whose output gets weaker the hotter it becomes. When the problem occurs, feel the coil to see how hot it's getting. If it's too hot to touch, replace it.

Also, it wouldn't hurt to take a look at your plugs and see what's going on inside the cylinders. Do a search on the web for how to read the plugs. It takes a fairly trained eye to make a reliable diagnosis but there are some basics you can look for.

I'd also like to ask, what kind of shape is the gas-tank in?

If there's a lot of sediment floating around in there it could all be getting sucked up by the pump, and after a certain period of time making nice little clogs, keeping an adequate fuel supply from ever reaching the carbs.

I'm inclined to agree with Enigma and would lean more towards the coil being the problem.

Adam,

I wonder if it could be the condensor breaking down. What do you think ??.

Rick.

:devious: :devious:

Are the spark plugs new? I had a 4-Runner with a broken plug insulator, it worked 92% of the time, and had an intermittent miss. I pulled the spark plugs and they looked OK (I was looking at the business end, not the insulator) and put them back in. It cost $150 for the sealership tech to tell me what I missed!!!

I wonder if it could be the condensor breaking down. What do you think ??.

I belive all 260Zs have electronic (breaker-less) dizzys so there shouldn't be any condensor. My understanding is that these are used to prevent the burning of ignition points.

Hey there Adam,

Sorry mate, but my 260 has a condensor (capacitor), and missing of the engine after a period of running can indicate a faulty condensor.

Rick.

:devious: :devious:

I agree with kdmatt, try the fuel tank first then the coil. Same thing happened in my 76 ran around in circles for two months. Got fed up and dropped the tank. I didn't have the cash to have pro cleaned so I got out as much junk as I could and rerouted the fuel feed line to my drain plug hole. I went through about four fram g3 filters before I got all the junk out. Car runs like a champ. You can test this by jacking up drivers side, shake the hell out the back of car let set for five minutes. While leaving the fuel cap on, remove drain plug and drain into a clear container, if you have junk in there you'll see it right away. Then it's up to you how you go from there. Good Luck! I hope you get it figured out cuz a Z that sits, well that's just not right. Dan

Sorry mate, but my 260 has a condensor (capacitor), and missing of the engine after a period of running can indicate a faulty condensor.

Rick, I don't want to hijack the original topic but I must appologize, I was caught thinking American market only again. Did your 260Z come with a mechanical distributor from the factory?