Intermittent loss of power on climbs

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macklen
Posts: 25
Joined: Sat Dec 21, 2013 7:15 pm
Car: 1985 Nissan 720

Intermittent loss of power on climbs

Postby macklen » Sun Apr 10, 2016 3:18 pm

Hello everyone.
I have a problem that comes and goes on an otherwise decent running 720 with a Z24. Hopefully someone can shine some light on the matter.

At times, it seems to kinda choke off under acceleration, most noticeably on a long climb. It gradually loses power and then sputters and vibrates as if it was gonna stall, then I release the throttle pedal and it goes back to idling normal, but loses the momentum to finish the climb. I have detected the smell of unburned gas when I reach the top of the hill, and it appears to give crappier gas mileage on the days when the bug rears its ugly face. On even, flat terrain, it runs like a champ.

The first time this happened I replaced a few hoses that were cracked and the fuel filter and pump, and it got better for a while.
Another time, it ran crappy for a week, then it fixed itself :wtf2: just when I was on my way to borrow a timing light to check the timing. I decided not to fook with it for the time being. Ran great for about a year.

Then, last week, while fiddling under the hood to do absolutely nothing of consequence, I removed the air cleaner assembly and I must've somehow kicked the elusive bug awake, since it's been running crappy for the last few days.

I figured it was something right under the filter, so I cleaned the carb with a can of spray, checked hoses and connections again, adjusted the idle speed, turned mixture screw in both ways *(which apparently did nothing at all), but the truck is still suffering to make long climbs, and stalls sometimes. Again, if I release the throttle pedal it returns to idling fine, but then I'm stuck midway up the hill.

It has good spark plugs and wires, cap and rotor, new fuel filter and pump, and all the emissions hoses but the vacuum advance have been properly capped off and forgotten about.

I am saving to throw in a Weber carb, but it seems a shame to discard the stock one since the truck runs and idles great, except on those rare days when this issue shows up.

Any advice?? :gotme


Tokin
Posts: 6
Joined: Sun Nov 08, 2015 10:03 pm
Car: 84 720

Re: Intermittent loss of power on climbs

Postby Tokin » Thu Apr 14, 2016 7:16 pm

There is a fuel pump relay mounted on the inside firewall on the passenger side under the dash. Either replace it if you can find one or fold a little tin foil and slide it between the relay contacts. I had a friend who went thru this and went so far as to replace the fuel pump and was disappointed when it happened again. Then he learned of this relay..

macklen
Posts: 25
Joined: Sat Dec 21, 2013 7:15 pm
Car: 1985 Nissan 720

Re: Intermittent loss of power on climbs

Postby macklen » Wed Jul 20, 2016 3:06 pm

Deleted AB valve and plugged port. Problem seems to have gone away.

ibjman
Posts: 30
Joined: Tue May 12, 2015 5:36 pm
Car: 1986 720 King Cab Z24
Location: Phoenix

Re: Intermittent loss of power on climbs

Postby ibjman » Sun Aug 28, 2016 1:02 pm

I'm feeling dense here, but what is "AB" valve


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