Pickup sputters uphill

[Ejack]

Hey all! I have a 1984 Nissan 720 KC 4x4 pickup. When I go up hills (heavy load) my truck sputters and stumbles like it's running out of fuel. Not quite sure what's going on because I just did a major tune up. New gas tank, fuel pump, fuel filter, carburator (Weber), cap and rotor, plugs and wires. My thought is to adjust the fuel ratio screw or the carburator float level. Any ideas before I start tinkering are appreciated!

 

Picture of plug attached.

[datzenmike]

A new Weber??? Was it running alright before? or was this carb put on with all the new parts?

 

 

 

Confirm that all the wires go to the correct plugs.

 

 

 

Do you have this distributor? Has three wires in a harness with a separate wire with it's own plastic plug?

 

 

 

 

 

[Charlie69]

Does your Weber connect to the same steel fuel line as the stock carb did that comes up between the manifold and the head?

 

 

https://forums.nicoclub.com/how-to-put-a-weber-32-36-on-that-shaggin-waggon-t566083.html

[Ejack]

13 hours ago, datzenmike said:

A new Weber??? Was it running alright before? or was this carb put on with all the new parts?

 

 

 

Confirm that all the wires go to the correct plugs.

 

 

 

Do you have this distributor? Has three wires in a harness with a separate wire with it's own plastic plug?

 

 

 

 

 

Brand new Weber. All the new parts were put on at the same time as the truck sat for 10 years. The truck actually runs really good and pulls good. It just has this intermittent issue under really heavy load. Wires are correct, and yes that is my distributor. Haven't replaced the distributor with a new one.

[Ejack]

13 hours ago, Charlie69 said:

Does your Weber connect to the same steel fuel line as the stock carb did that comes up between the manifold and the head?

 

 

https://forums.nicoclub.com/how-to-put-a-weber-32-36-on-that-shaggin-waggon-t566083.html

Yep! Same steel line.

[datzenmike]

10 minutes ago, Ejack said:

 Haven't replaced the distributor with a new one.

 

Lord, don't do that!!! The factory one is way better than anything you can buy. The best way to replace things is one at a time so you know what part has caused a change in running.

 

Runs well except under extreme load is likely the carb running short of gas. Float may be too low or pump not delivering.

 

There is a fuel filter on the twist off bottom of the electric pump, and a magnet on the cap.

 

Pull the fuel hose off and direct into a suitable container. You should get about 1.4 liters per minute with the electric pump on.

[Madkaw]

Also haven’t mentioned coils . Make sure their connections are good . That’s the ideal scenario for a bad coil to shows it face . Spark isn’t able to jump the gap for a weak charge . 
Double check for vacuum leaks with those damn Weber adapters . 

[datzenmike]

Under load the Z24 has a vacuum switch that turns off the exhaust side coil. This is why I posted the distributor picture.

 

Unplug the single wire and the distributor is forced to fire both coils all the time. If it clears up then maybe the intake coil. Don't go buying coils, this is just a fact finding exercise right now.

[Ejack]

4 hours ago, Madkaw said:

Also haven’t mentioned coils . Make sure their connections are good . That’s the ideal scenario for a bad coil to shows it face . Spark isn’t able to jump the gap for a weak charge . 
Double check for vacuum leaks with those damn Weber adapters . 

The coils are also new. Forgot to mention those. No vacuum leaks that I can hear, but I will however spray some carb cleaner around the adapter just to be sure.

[datzenmike]

I'm a firm believer in not fixing something that is not broken.  Do you still have the old ones? Never throw away parts.

[Madkaw]

How many turns out on the idle jet? Is that a 32/36 carb? 
Looks like a typical spark burn of a rich idle and lean loading. These carbs are stupid lean at moderate and heavy loading unless you turn out the idle jet 2 turns . 
Lean condition might give more of a popping than a studder. 

[Ejack]

On 3/21/2020 at 12:21 PM, datzenmike said:

Pull the fuel hose off and direct into a suitable container. You should get about 1.4 liters per minute with the electric pump on

Just did this test. I'm only getting 1 litre per minute with the engine not running (12v). The fuel pump I have is the Autobest F4329 (brand new)

[datzenmike]

Volume seems ok, after all you are not going to need a liter of gas a minute when driving.

[Ejack]

Checked voltage to the pump for good measure. A steady 11.4v going to unplug the distributor wire and go for a hard drive

[Ejack]

Just got back. It took a solid 30 mins of driving for the issue to finally pop up. Unplugging the distributor seems to have no effect. I did notice that before I was having the issue, the idle is normal (800-1000 RPM). Once I got back to my driveway the lowest idle I could get was 1200 RPM, AND when I just barely touch the idle, the truck revs up to 4k RPM then comes back down... that's new. Perhaps when the truck gets warm enough after enough sustained driving, something expands and causes a vacuum leak?

[datzenmike]

I don't know Weber. Is the choke on at all, even partly. This would partly engage the fast idle cam. Is the throttle cable too tight? Is the secondary barrel closed tight?

 

 

Before I forget... have you adjusted the valve clearances?

[Madkaw]

Have checked for vacuum leaks yet? Those adapters are leaks waiting to happen . I used Loctite on all the studs and sealer on the gaskets . 
You haven’t mentioned the settings on the carb

[Ejack]

2 hours ago, Madkaw said:

Have checked for vacuum leaks yet? Those adapters are leaks waiting to happen . I used Loctite on all the studs and sealer on the gaskets . 
You haven’t mentioned the settings on the carb

No leaks. Also, I have not touched the carb settings except for the idle speed screw. I figure Weber knows their carbs better than I. The reason I am hesitant to start fiddling with the settings is because the truck runs great at idle and for 30 mins of driving! It's only after everything gets warmed up that my issue arises.

[banzai510(hainz)]

Your choke flap is maybe still closed or partialy closed

webers are simple and ez

if runs for half hr ok either it’s a choke flap adjustment issue 

however I’m not a 720 z series expert as they have lots of emission tubes

Edited March 23, 2020 by banzai510(hainz)

[Charlie69]

That is the correct way to get gas to the Weber.  I am curious does your rubber line make a loop to connect the rubber line to the Weber from the steel pipe?  I will take some pictures of my Weber To see if maybe you have a vacuum Line wrong.  I do not use the A &B valves on the inner passenger fender.  I do use a cat and oxygen sensor.  I also use the EGR.  I have to emission test my 86 kin cab every 2 years here in Phoenix.

 

The gas cap also should seal and is not a venting gas cap.

Edited May 14, 2020 by Charlie69

[datzenmike]

Good one Charlie! Maybe the loop in the fuel line is kinked????

[Charlie69]

I have seen many people install a Weber DGEV with a loop in the line Because the position of the steel line and the position of the Weber inlet conflict and in order to not kink the rubber hose you have to loop the fuel line.  I use a round shanked Phillips screw driver that just fits in the steel line and then support the pipe on the side I am going to bend it with my fingers to help not kink the steel pipe.  I go real easy adjusting the pipe position a little at a time and checking with the hose to see if the hose will go on with out kinking.  Also do not insert the screw drive past the "Y" as you will not be able to bend the line at or be low the "Y".  I usually take about 10 or so tries before I get the pipe in a position I can connect the short piece of rubber fuel line.  It is easiest to use the low pressure fuel line for carbs not the fuel injected fuel line that most parts store people will sell you.  The quality of the help in parts stores really sucks these days as they are fore the most part younger people that first do not know carburetion and also if it is not on the computer they are not capable of using a paper parts catalog.

 

I will post pictures in a little while of how my line is fitted.

[Madkaw]

Good point about a collapsing rubber hose. Makes sense that it gets hot and then the rubber gets soft and collapses. 

[Ejack]

Thanks for all the suggestions on this issue. I finally found out that it was a clogged fuel filter. Pretty embarrassing but in my defense, it was only 6 months old with a brand new fuel tank. I have a feeling the new tank had debris in it from the manufacturer which caused my filter to clog prematurely. I hope someone can learn from my frustration. Don't rule out new(ish) parts!

[Draker]

Not as embarrassing as just being out of gas. 🙂

 

Glad it was something simple.