720 starts but won't idle

[Broke down meow]

I've had my Nissan 720 for about 3 years now, over 250k miles, and have only had a problem with the alternator and starter and a head gasket leak. Just the other day, it began to sputter down the road and whenever I wasn't pressing on the gas pedal, the engine would die. It starts just fine but it won't idle. I checked the fuel pump with a jumper cable and made sure fuel is making it to the carb. Could it be something to do with the choke? The choke flap is completely open whether the engine is running or not.

[]2eDeYe]

Most likely the idle solenoid got disconnected or is no longer functioning correctly. 

 

 

Edit: sounds like you choke is also out of adjustment, being wide open though it would not affect the idle unless the motor is cold. 

[Broke down meow]

How would I check the solenoid?

 

Other than turning the key back and forth.

[]2eDeYe]

It's been a while, but there should be a wire leading to it on the carb. It should have +12v with the ignition on. 

 

You can remove the solenoid and test it by applying +12v to the plug and grounding the body, the actuator will move in or out and should move the other way when you remove power. 

[datzenmike]

Z24s are notorious for blowing the head gasket a 100K intervals. This usually causes sudden very poor running and no idle.

 

 

One or two wing nuts holding the air filter on??? This determines if you have a carb or EFI.

 

1/ One is carb. Two possibilities here. Regular carb and electronic feedback. Look at the electrical plug on the back two wires? Or 6 wires on a large round plug??

 

2/ Look on engine tag... pass side inner fender below hood hinge. ENGINE Z24 (carb) or Z24i??? (EFI)  EFI was available April '85 and there will be two wing nuts and there wouldn't be an idle cut.

[]2eDeYe]

Totally did not think of EFI :lol: 

[Broke down meow]

Definitely not an EFI. And there's two wires coming off the solenoid and they go to a connector with six wires on it

[Broke down meow]

So, I took that solenoid off and removed the pin and spring and it idles just fine now!!! In theory, would I be able to keep running it like this? Or do I need to replace the solenoid?

[]2eDeYe]

I would replace the solenoid to keep the system working correctly. 

[Broke down meow]

Do you know if it'll run until I can get a new solenoid?

Like a week or so?

[]2eDeYe]

Probably, but it will probably run real rich. 

[LenRobertson]

I ran my L20b 510 for years without a needle in the idle cut solenoid. I never noticed any problem with it running rich but maybe I missed something. It was a Hitachi 340 carb and there may be something different on the newer 720 carbs. The main problem is without a working idle cut, when you turn off the key the engine is apt to want to keep running for quite a few seconds depending on how hot it is. This is rather annoying but you can kill it by stepping on the brake and letting out the clutch with it in gear. Or floor the gas pedal as you turn the key off.

 

You should screw the solenoid back in the hole after removing the needle and spring.

 

Len

[datzenmike]

Did it click when the ignition cycled on off on off on off??? Can or did you check for the 12 volts when key is on. If the power isn't there, a new one won't help, in fact the old one may be fine..

[Broke down meow]

I am trying to take a multimeter to the solenoid but how would I test it? It looks like there's no way to remove the wires to test the leads

[datzenmike]

Definitely not an EFI. And there's two wires coming off the solenoid and they go to a connector with six wires on it

 

 

So, I took that solenoid off and removed the pin and spring and it idles just fine now!!! In theory, would I be able to keep running it like this? Or do I need to replace the solenoid?

 

 

 

Idle cut solenoid....

 

Unplug the 6 wire connector. Test the Red/Yellow stripe wire for 12 volts when the key is turned to ON. Beside it is a Yellow wire that should be grounded. The carb side is a Red wire becoming Red/Yellow on the harness side. The ground return is the Black wire becoming Yellow on the harness side.

 

Carb side Red........ Red/Yellow engine side.... should have 12 volts with key on

Carb side Black..... Yellow engine side............. should be grounded.

 

This plug and the short wires are known to be a problem. The wires do not flex because they are too short. They tend to break inside the insulation from pulling the air filter off and on. Expect to find it works intermittently if connected and you wiggle the wires around.

[BearForceOne]

I'm experiencing nearly identical problems. 
Rebuilt my 1985 Z24's carburetor and noticed the anti dieseling (I assume the same part as the idle) solenoid was missing it's needle and spring. For about a week after it being rebuilt It ran as perfectly as I've ever seen. Just yesterday though the idle became really rough like it was before the rebuild, and taking it out for a drive it would stall any time I wasn't babying the throttle. Also the exhaust sounds like there's a compression leak (sort of a shuh noise) though I adjusted the valves about a month ago to fix a misfire. I screwed with the idle adjust screw and fuel adjustment screw enough that it does idle now though rather high, and it's back to running very rich. 
I did notice in the carb rebuild the wires to the solenoid were not only twisted heavily but the insulation was breaking apart and falling off. Should I try to find another carburetor for it's solenoid or what can be done with the needle/spring missing as it is now?

[datzenmike]

I'm experiencing nearly identical problems. 

Rebuilt my 1985 Z24's carburetor and noticed the anti dieseling (I assume the same part as the idle) solenoid was missing it's needle and spring. For about a week after it being rebuilt It ran as perfectly as I've ever seen. Just yesterday though the idle became really rough like it was before the rebuild, and taking it out for a drive it would stall any time I wasn't babying the throttle. Also the exhaust sounds like there's a compression leak (sort of a shuh noise) though I adjusted the valves about a month ago to fix a misfire. I screwed with the idle adjust screw and fuel adjustment screw enough that it does idle now though rather high, and it's back to running very rich. 

I did notice in the carb rebuild the wires to the solenoid were not only twisted heavily but the insulation was breaking apart and falling off. Should I try to find another carburetor for it's solenoid or what can be done with the needle/spring missing as it is now?

 

 

Z24s are well known for blowing their head gaskets and they lack power and have a strange exhaust sound. Check you valve clearances again in case you closed one too tight. Set them hot at 0.014".

 

A compression test may show two adjacent cylinders low if blown between them.