Terrible to no idle

[elfirebeasto]

I have done some searching around here and the net in general for about a week and a half. I have found a few things that describe, for the most part, what my problem is. They each have solutions, but not all are the same solutions. Here's my issue: Sometimes, when cold, the truck will idle at around 1500 rpm, but it sounds like total crap, barely able to keep itself alive. When warm, it has no idle what so ever. Anything below 2k is dead. When I'm driving, anything below 2k bucks and hops and feels like the power just isn't there. The problem wasn't as bad before my carb rebuild, but after it got very matter of fact on where it would run properly or wouldnt. The reason for the carb rebuild was to fix the idle issue, and maybe get better fuel economy.

 

Here's what I've learned: The anti-diesel solenoid doesn't click when unplugged with the ignition on, so bad solenoid...maybe. I also have a green wire running to my throttle valve switch that is disconnected inside the plastic carb electrical connector. I don't know what that controls and can't seem to locate info on it, but I'm sure it's not helping anything. I was planning on installing a jumper to correct that issue. I just replaced the couple remaining vacuum hoses on my system, and capped any openings I could find. That did seem to help some, allowing it to run down to 1500rpm, but sound like it wanted to die. Also, I may have a fuel over pressure problem...Is the fuel line supposed to sit at the dot in the fuel glass window? I adjusted the new float to factory specs when I installed it with the carb rebuild. Both before and after rebuild the fuel level was far above that dot (level not visible in glass). So which possible issue seems to be the most probable, or could it be a combination of all?

 

I'm not sure where to start...I need guidance! Thanks for the help!

[datzenmike]

Fuel leel should be at the dot.

 

Does your carb have a round connector with 4 or 5 wires or a small one with two???

[TENDRIL]

sounds like your running way to rich, until you get above 2k, where at that point there is way more air being sucked in and it starts to even out!! green wire elect. choke?

[ggzilla]

Start with the antidiesel solenoid. Unscrew it, pull the pintle & spring out, and screw it back in. That will let it idle.

When the solenoid is bad, you won't under under 1500-2000 RPM, but it will start and idle under the choke.

 

Once you get it running, then set the float level to the correct spot (on the site glass).

[elfirebeasto]

Fuel leel should be at the dot.

 

Does your carb have a round connector with 4 or 5 wires or a small one with two???

 

 

Large, with 4 or 5 wires I believe. 2 anti-diesel, 1 throttle switch, 1 choke heater and maybe one more.

 

Start with the antidiesel solenoid. Unscrew it, pull the pintle & spring out, and screw it back in. That will let it idle.

When the solenoid is bad, you won't under under 1500-2000 RPM, but it will start and idle under the choke.

 

Once you get it running, then set the float level to the correct spot (on the site glass).

Thats what I was thinking of doing with the solenoid. As for the fuel level, I guess I can bend the tab on the float well beyond the factory setting. I think I may have a clog on my fuel return. But I will check it out. When I owned the truck the first time, it ended up shoving fuel into the intake when ever the pump was running, as if that were the only escape for the fuel pressure. Thanks for your help guys. I appreciate it

[elfirebeasto]

sounds like your running way to rich, until you get above 2k, where at that point there is way more air being sucked in and it starts to even out!! green wire elect. choke?

I believe electric choke is blue on mine, or at least choke heater. The green wire goes to the throttle switch, which I guess depresses when the throttle is shut, closing the circuit.

[vabeach454]

Mine runs way better with the switch unplugged and only blue wire (Choke) hooked up. I will be switching to the WEBER 32/36 Kit soon.

[ggzilla]

when ever the pump was running

You can solve that problem by fitting a stock mechanical fuel pump. The datsun pump is high volume, and needs no regulator or return line. The stock fuel pump pressure is internally regulated, even if you have a plugged return it won't over pressure the carburetor.

[datsunaholic]

An '85 720 won't have anywhere to put a mechanical fuel pump. The Z24 engine doesn't have the hole machined out for it. All z24 720s from mid '83-on had stock electric pumps. And yes, the mechanical pump needed a return line, starting with the L20B in '75. The pump was a lot higher volume than the old L16/L18 pumps, and just slightly higher pressure than the floats can handle, particularly on old carbs with iffy floats and needle seats.

 

You want to get that return line cleared out.

[datzenmike]

By the sound of it you have the electronic feed back carb. Do you have an O2 sensor in the exhaust manifold?

 

 

Red is idle cut solenoid

Black is ground

L is the symbol for Blue for the electric choke

GW is Green/White stripe is the throttle switch that tells the computer ECU if you are at idle or not.

YB Yellow/Black stripe and White is for the air/fuel ratio solenoid.

 

 

 

 

All this stuff has to be connected and working. Info from the throttle switch and the O2 sensor goes to the ECU which adjusts the air fuel ratio by adjusting the air/fuel ratio solenoid. While the choke is on and the engine cold, this is in open loop mode. Once warned up it goes into closed loop with feedback from the O2 sensor to keep the air/fuel ratio within programed limits. If there is a fault the system defaults to an over rich condition so the truck can be driven... (presumably to get it fixed)

 

It is a well known problem that Nissan used wires that are too short on this round connector and constant flexing breaks the wire inside the insulation.

[vabeach454]

It is a well known problem that Nissan used wires that are too short on this round connector and constant flexing breaks the wire inside the insulation.

 

 

Why even mess around with a 25+ year old carb... When you can buy a new Better One for cheap?

 

 

http://www.ebay.com/itm/130674168186?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

[ggzilla]

Yes, why mess with an old pickup when you can buy a new better one for cheap? Because we at Ratsun are recyclers not consumers.

[elfirebeasto]

Yes, why mess with an old pickup when you can buy a new better one for cheap? Because we at Ratsun are recyclers not consumers.

 

And because I can't afford $265 for a new webber. I can barely afford a new idle cut solenoid at $50+. In a house of 5, I'm the only one working @$10.50/hr. Broke as a joke. So, I'm kind of stuck trying to fix things on junkyard parts and left over scraps from other peoples vehicles.

 

I haven't tried to fix this whole thing yet. I've been busy trying to get a home business off the ground while keeping to the kids' appointments and work, plus the random family things that come up. Sheila is my DD, so I can't put her on the back burner. I may be doin it in the dark tomorrow. 6 hour round trip to get my son to the doc tomorrow.

[elfirebeasto]

By the sound of it you have the electronic feed back carb. Do you have an O2 sensor in the exhaust manifold?

 

GW is Green/White stripe is the throttle switch that tells the computer ECU if you are at idle or not.

 

I do indeed have an O2 sensor. and as far as the green/white wire, inside the connector, the pin on that wire (on the carb side) is messed up, and doesn't seat into the receiver on the truck side of the connector. I may install a jumper and see if that helps. And I have yet to actually go remove the needle from inside the idle cut solenoid.

[ggzilla]

When your engine won't idle, always check the idle-cut solenoid first. You don't have to replace it, your engine don't need one to run well. Removing the pintle will fix it.

 

It's a 5-minute job. And will either fix the idle problem or won't.

[elfirebeasto]

Roger, gg, I wil have to get out there and do that. I keep meaning to, but damned if something doesn't come up right when I'm about to do it.

[radracer]

"It will either fix the problem or it wont." lol

 

thats the kind of common sense, "go get it done" attitude that is making this place my fav datsun owners site very quickly.

 

I like it here :D

 

 

(though I AM going to be getting that webber carb before my project is done :P )

[elfirebeasto]

I pulled it and the engine decided it needed to idle at 3k. I then cleaned the hole, and shoved it back in, now it slowly climbs to 3k. I did notice, though, that the choke being opened or closed didn't change the idle...maybe when I put the carb back together, I didn't get the secondary side aligned properly and its binding slightly open. Any thoughts?

[ggzilla]

Possible. Yes, next I would check the throttle blades, make sure both are closing all the way (when choke is open)

[ggzilla]

don't give up

[ggzilla]

It's got to be something simple. Maybe an air bleed is loose. Use a flat screwdriver, don't get them too tight, just make sure they aren't loose .You can see them on the top of the carb with the air cleaner removed.

[elfirebeasto]

Do you have a picture of the air bleeds? I think I know what you are talking about but id rather be certain

[ggzilla]

Just see if any screw is loose thats on the top of the carb.. Air bleeds have a straight slot, not philips. As long as you don't overtighten you can't break anything. Just use finger and thumb on the screwdriver to make sure they are not loose.

[elfirebeasto]

Will do

[ggzilla]

Anyone who has seen my posts knows that my carb is screwing me around...I thought I had finally found the real reason for my high idle. I thought there was just too much air getting into my engine. Well, I sealed the base, I checked vacuum lines the best I know how, and I fixed the throttle plate on my secondary which used to stay cracked open slightly because I misaligned it when I did the rebuild. I even checked the anti idle solenoid. The only thing I can think of that is left is to put a jumper across the throttle switch to make sure the circuit is working, as the plug is messed up and doesnt allow the pin for the switch to make contact inside the connector. I do know that my fuel is flowing just too high. No matter how I set the float, it just keeps pumping into the bowl. I think the newer pumps are too high pressure or something. Its had these issues before the rebuild. I kinda thought rebuilding would fix some of the problems. Is there something simple I'm overlooking or maybe I'm just over thinking this? I need my truck back. Please help

 

Thanks,

Brandon

 

Previously you said it idled around 1500 rpm. Have you fixed that, and now is idling around 800 rpm where it belongs?

 

Here are the previous suggestions:

* Fuel level should be at the dot

* get that return line cleared out

* ensure that carburetor top screws & jets are not loose (the visible ones on the top of carburetor)

 

What are your results from these suggestions?