Truck has around 150k miles. It started cutting out on me a few months ago around 40 mph or higher. The idle was acting strange, started fine but after a few minutes... idle goes crazy and truck dies. Hard to start after that but, once started it'll idle again and die again (unless driving and then just seems to cut out).

First thought it was the fuel pump (one of those generic pumps) and replaced with another and new filter. Still acted up and cutting out. Later found the accelerator pump was leaking by gas. Changed out but, still seems to be cutting out
around 40 mph or higher, also seems to not have any power. Idle and die issue has stopped with the change of the acc. pump.

Keep hearing a clicking noise from under the dash. Know about the relay but, doesn't seem to cause the truck to run
better or worse when it clicks. Seems to do after hitting a bump or going over railroad tracks.

Never rebuilt the carb., replaced head gasket twice. That's my story, owned the truck for 30 years and only drive to work about 7 miles each day to a chemical plant. Keep thinking about getting another vehicle but, can't. It's like a kid to me and has sentimental value and will probably keep until it's a pile of rust.

Thanks for any ideas.

Update, this weekend replaced rotor, distributor, spark plugs and wires. Also cleaned the pump relay and check the
solder joints. Put everything back together and still cuts out.

I think you may have a fuel starvation problem. I had this issue with my truck just over three years ago. Anything under 50km/h (30mph) was fine, but doing 60km/h (40mph) or higher and the truck would cut out.
Next time you drive the truck and it cuts out, pull over and check the level in the carb window, if there's not enough gas getting to the carburetor then the truck will cut out.

Likewise I replaced the fuel filter and the fuel pump, still no joy. Checked the relay, that was fine. In my case the issue was a partially-blocked fuel pipe, after taking an air compressor and blowing through the line a few times, the issue was fixed. I'd try doing this if you haven't already done so. ;-)

I have 84 nissan datsun 720 truck and having similar problems. When i start truck it idles crazy like bad miss and if i take foot off gas will die out before it got this bad was backfiring alot also. Use to after it died out it would take a while to start back running and it would run fine now its constant. Changed alot of relays and put new coils in pump and filter plugs distributor cap and wires the fuel pump relay and auto choke relay i changed also. Wierd thing is wheni start it at nite after weather cools down it runs like a new truck no bad idle or missn or backfiring runs perfect but when i start it during the day the hot weather is effecting it somehow i dont get it but it jist wont run. Anybody have a clue?

Ajack wrote:I have 84 nissan datsun 720 truck and having similar problems. When i start truck it idles crazy like bad miss and if i take foot off gas will die out before it got this bad was backfiring alot also. Use to after it died out it would take a while to start back running and it would run fine now its constant. Changed alot of relays and put new coils in pump and filter plugs distributor cap and wires the fuel pump relay and auto choke relay i changed also. Wierd thing is wheni start it at nite after weather cools down it runs like a new truck no bad idle or missn or backfiring runs perfect but when i start it during the day the hot weather is effecting it somehow i dont get it but it jist wont run. Anybody have a clue?

I had basically the same issues on my '86 720. Three main issues were vacuum leaks, badly adjusted choke and a dead ECM. I think in '84 they went over to computer-controlled carburetors in the 720. If that's the case on your truck, a dead engine computer won't be able to set the proper air/fuel ratio, and your carb will run full rich. If you keep your foot on the throttle the engine can suck some of that extra fuel down, but once you release it it becomes too much and the truck dies. Cool air is denser, which gives you more oxygen in the same space; so it might burn more easily with the extra fuel. Warm air isn't as dense, so can't burn properly with extra fuel in it.

it wont idle check the vacuums. cuts out check the fusable link at the + battery and all the vacuums. mine drove me nuts that's what fixed it