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Need help/suggestions with 720 truck! Engine won't stop turning over when turned off!!


Tspite

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I have a 1985 Nissan 720 king cab ST (Auto). 106 k miles, Engine has been doing some weird things after driving a bit and after its warmed up, parked and I turn the ignition off it starts sputtering, at first we thought it was a timing issue or an electrical problem, but everything else seems to be functioning.

 

Here is where it gets really weird.. We did a test and when it started acting up we unplugged the coils with the battery hooked up, and again with the battery unplugged as well (Just did it to see what happened).. It just acts like it still wants to start is the best way I can explain it, like its wanting to keep on going, only it stalling out in the process.. 

 

It never stalls or over heats in traffic, but it does lack alot of power. Very smooth truck, we plan on doing a compression check but I want to see what you guys think or if any of you have experienced this. 

 

 

 

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Might have an overly rich idle mixture contributing to the problem, and/or too fast idle, and timing can make it worse.  Basically, do a tune-up.  You can also try a Seafoam treatment to help clean out carbon build-up.  You get the engine fully warmed up and slowly pour (trickle) Seafoam down the carb with the engine running...about 1/3 the bottle, then put the rest in your gas tank (the less gas in the tank, the higher the concentration obviously).

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Do you have the stock carb? You should be hearing the click of your anti-dieseling solenoid. Sounds like its working, but I'd take it off and clean it and the hole it goes into, just to be sure its not sticking open or something. Usually helps overall to do a carb rebuild. Also, check your timing and make sure it is not very far advanced.

 

Oh and check your fuses. On my older-model 720, the choke and the anti-dieseling solenoid are on the same circuit, so if you have a burnt fuse it would not open the choke fully or operate the solenoid. Either of those could cause dieseling.

 

Good luck.

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Is this truck normally driven on a regular basis? So if yes, then it just started happening? Or did you just get the truck? Did you do anything to the truck before this started happening?

 

Sounds like carbon buildup to me, which could be exacerbated by a rich mixture. The rich mixture could be a dirty carb.

 

We used to do what we called an "engine douche" where we would remove the air cleaner and rev the motor to about 3000 to 4000 rpms and then pump water from a garden hose down the primary venturi of the carb while running. It totally works, but I probably wouldn't try that any more. Ignorance is bliss...

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arizonajones: Yes its the stock carb, I bought it from a previous owner a few months ago, the driveshaft was broke. Got that fixed,and now going to engine. my plan is to A. Get a compression check because I'm pretty sure the head gasket is bad too.. 2nd: check timing, carb does need a rebuild but I might just get a weber.

 

Another thing I noticed is a buzzing sound coming from the passenger side when I have the accessory on, as I also can hear the fuel pump turn on. Is that normal? Sound's like a relay

And on my carb the electric choke flap is wide open, Normal?

 

Just wanting to get this truck squared away for daily use, I think it's worth saving in my opinion. After so I want to get onto my S30. 

 

Much appreciated for the input guys!

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  • 2 weeks later...

It's not normal.

 

 

arizonajones: Yes its the stock carb, I bought it from a previous owner a few months ago, the driveshaft was broke. Got that fixed,and now going to engine. my plan is to A. Get a compression check because I'm pretty sure the head gasket is bad too.. 2nd: check timing, carb does need a rebuild but I might just get a weber.

 

Another thing I noticed is a buzzing sound coming from the passenger side when I have the accessory on, as I also can hear the fuel pump turn on. Is that normal? Sound's like a relay

And on my carb the electric choke flap is wide open, Normal?

 

Just wanting to get this truck squared away for daily use, I think it's worth saving in my opinion. After so I want to get onto my S30. 

 

Much appreciated for the input guys!

 

That's the choke heater relay and it does that when your charging system is not right. To have the choke heater on and working you need the alternator charging. Low output will cause the relay to buzz. When it's low or failed, the relay will click on and off quickly and buzz. If the choke heater isn't working your electric choke will not warm up and shut off fully. If the choke stays part on it will run rich and carbon up, leading to dieseling and run on. Another symptom of the choke not shutting off is the fast idle circuit will also be on to help speed up the warm up process.

 

When warmed up the choke plate should be open like this...

 

carb720shouldlooklikethisLarge.jpg

 

... not closed or part closed like this...

 

carb720notlikethisLarge.jpg

 

Has your alternator been replaced recently? Something electrical is wrong with it.

 

Your gas mileage is likely very poor now too right?

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