The 720 4x4 from Hell

[TotalPleb]

I recently made a reallllllllllllllly rushed decision to buy a high mileage, nearly rust free, not totally daily ready '85 720 4x4 with the carbed z24. Did I also mention that I have no knowledge of manual transmissions as far as operating them.....?

So, before my family rips my head off and shoves my shame down my throat..... I need some help.

 

It runs pretty poorly. I can tell the timing is off, the aftermarket carb doesn't have the electronic bits hooked up and runs rich, OMG the stuttering and backfiring are atrocious, and I'm pretty sure I wired the ignition wrong (although it ran better than when I bought it, so¯\_(ツ)_/¯).

I have a week-long layoff, so I have time to get it daily ready. I'm really in need of some wiring help, I might be a tooth off on timing, and I probably just need to do a crash course style carb clean on the extra stock carb that came with the truck.


I just bought my sorta dream truck, and I really don't want to have to post it up online as parts because I don goofed. Please help!

[datzenmike]

There's no reason to suspect the timing is off a tooth unless the drive spindle has been removed and put in wrong. The distributor can't be put back in in the wrong position. Get a timing light and do it right.

 

Check the firing order. There are 4 intake alternating with 4 exhaust plug wires on the cap. Very easy to get two out of place.

 

 

Check and set the valve lash on a HOT engine. 0.012" on all valves.

 

Need more info. Why would you need to wire the ignition? Why would it be apart?

 

You probably have a Weber 32/36 carb on it. If you have the stock carb that would be the best for it. Get it running and then swap the carb to the Weber.

 

As always, pictures really help, so post all you like.

[TotalPleb]

I'll post some detailed engine bay pics in the morning. The current carb is one of the cheap replacements you find on eBay.

I suspect something is really off because I lost power today and backfired, then anything more than a hair of throttle causes massive lurching like I was stomping the brake while accelerating. It even spit me out of first gear.

[TotalPleb]

The diagram you shared, I figured that all out in the first day. There are 2 in the center that I might have backward.

Idk.... oh yeah, it started itself when I turned it off and pulled the key. It turns off and ends with a rough shaking, but this time it actually fired up at that point.

[datzenmike]

The intake side and the exhaust side coil wires can be swapped. They fire at the same time so no difference really.

[TotalPleb]

I feel like I should list all of the issues so that the main problem can be diagnosed.

-The engine shakes at idle

-It backfires and occasionally loses power

-It stutters under driving load, mostly anything more than a light tap on the throttle

-It runs rich, smells like a go kart

-The blinkers work like there's a short, and turn signals work when they feel like it.

-It occasionally runs well, but then drives poorly.

-Low oil light on

-230,000 miles

-all of the electric bits from the stock carb are not on the eBay carb

---I'll add to this list as I remember.

[TotalPleb]

Welp, it was 1:30 a.m. and I had nothing to do, so I pulled the distributor cap.

May have found the source of a great deal of the issues.

 

Corroded, eroded, and dirty contacts. Replacement ordered.

[datzenmike]

Look ok, seen worse. Still, new ones eliminate them as the problem but it gets expensive throwing parts at a problem when it doesn't help.

 

 

Set the valve lash at 0.012" on all valves. Make sure engine is HOT. A tight valve can loose compression or leak intake vacuum.

Set timing to 3 BTDC with a timing light. Retarded ignition lacks power.

Check and remove any vacuum leaks from loose or cracked hoses. Make sure they are connected properly.

 

 

Backfire out the carb? Lean backfire can happen when cold if choke not set properly. Primary jet may be part blocked causing a lean backfire. Possibly spark jumping across bad wires. Check coil for cracks in the insulation.

 

Lurching on acceleration can be the carb float set too low.  Look at glass window on front of carb. Gas should be visible in the middle. Car is running out of gas.

 

Make sure all signal bulbs are good. The turn or emergency flashers are load dependent and need all bulbs working.

 

 

At 230K the engine

[TotalPleb]

I haven't been able to get to the site until now, kept have DNS server errors.

I replaced it because I went to pull it for cleaning and the rotor broke at the base. I'd rather have a fresh part at this point than try to mend that mess.

The carb on the truck was a Chinese knockoff with only one of the vacuum fittings and a missing fuel line, I just cannibalized parts off of it to repair the stock carb. The bad carb also was completely analog, with nothing in the way of sensors or even their mounts. Whoever installed it cut all of the corners possible, so now I'm replacing a ton of dry rotted vacuum lines that are all in the wrong places. (I'll take pictures in the morning so you get the idea of how annoying this mess is.)

I took the stock carb apart partially and cleaned the main parts of it, swapped out the bad parts with the Chinese parts, and placed it on the intake with a new gasket. I only went that far because I need to set up the new vacuum lines. I replaced the short bit of the fuel line before the carb because it was done for. That's my progress as of tonight.

I found out while I was inspecting the wiring situation that there is a vc gasket bolt missing, and it has caused a considerable leak. On the subject of leaks, the transfer case and possibly the rear diff have steady, slow leaks as well.

I'll check the lights and do some further testing when the carb is installed because the fuel pump is wired to the ignition and turns on when the key is turned.

I have to replace the vcg now, so I'll check the timing along with the valve lash when that part of the project comes along. I've never done either before, so this will be a definite first for me. This truck is a lot of firsts for me, but it's not my first pain in the @$$.

[datzenmike]

The metal fuel line next to the carb has a return line attached. Do not replace this. Fuel hoses you can replace.

[TotalPleb]

This thing?

(Stole from the interwebs)

 

That's one of the lines that the eBay carb was missing.

[TotalPleb]

I'm slowly realizing that this truck has been poorly treated and I'm definitely in up to my neck in maintenance/repairs...

 

edit: Ugh, this is a headache. I did not know what I was getting into. My mistake, but I'm not abandoning it. Time to work up some determination and power through as much of this as I can to get it back on the road.

Thank you, datzenmike, for staying with me so far. Your advice hasn't fallen on deaf ears, this truck will see another 230k miles.

[datzenmike]

 

 

The metal line besides the word 'starts' that goes down under the intake.

[datzenmike]

The missing hose is a vent for the fuel bowl. It's probably for a California carb. The fumes are collected by the charcoal canister beside the rad.

[TotalPleb]

My fuel was coming in through the line by the word start and the rubber bit there needed replacing. I need a repair manual like yesterday, this is so confusing right now.

[datzenmike]

You're doing fine.

[TotalPleb]

https://twitter.com/GrambleShmou/status/1015028946587570177

 

The video above will help a little with what point I'm at now.

[TotalPleb]

I have a feeling that the carb is from a truck with more emissions regulations than this truck has, or maybe my truck was in the process of a vacuum line delete.

 

I don't have the 2 ports coming off of the intake like the truck in the NICO vacuum line guide, so that info is proving sort-of irrelevant.

 

Here's a pic of the intake.

[TotalPleb]

Put the chinese carb back in. Got it to idle well and accept throttle taps, but putting it into gear was a terrible idea because it stalled out and hasn't started without choke since.

I'm closing in on having to go back to work, and I'm not really ready to ride the local bus route.

[datzenmike]

You don't have your location listed in your profile. If  north of Mexico it should have almost all the stuff in the NICO picture. Maybe someone deleted them.

 

Put in gear it stalled tells me you have an automatic. For good idle in gear, you need a good stable high intake vacuum. Any vacuum leak will screw this up. Make sure that electric heater plate under the carb has good gaskets and the bolts are tight.

 

Do you have an EGR valve on the rear of the intake? Has it been blocked off? Maybe the gasket is leaking.

 

 

Above all check/set the valve lash and time the ignition advance to 3 degrees before top dead center (BTDC) These two will really affect the idle quality.

[TotalPleb]

No, it's manual. I put it in first and it didn't like that.

[TotalPleb]

I set the valve lash and now have a decent idle at neutral. It's still bogging down with throttle input, so I might have a leak at the carb. I'll have to do some inspecting, but I'm getting close to a running, driving 720.

[TotalPleb]

So, it idles and accepts throttle input, but it's not letting me drive more than 40 yards without stalling out and acting like it doesn't have gas.

At this point, I have to pull the manual choke and find the spot it won't stall out in to limp it back to my house.

[datzenmike]

Fuel filter replaced?

[TotalPleb]

Fuel filter was dirty, but I sourced out the problem.

There was a kink in the fuel line with the pump was installed. I should have figured this out earlier when the carb took a while to fill up.

 

Here's how I figured it out;

I was fumbling around with the engine compartment fuel filter. Cleaned it out, blew some air through for good measure, then reinstalled it.

Turn the ignition to "ON" so the pump will kick in and replenish the fuel I had dumped out.... nothing. I can plainly hear the pump running, but it sounds forced.
Give the fuel pump a check to see it laying on the fuel line. Prop it up with a zip tie and BOOM, fuel pressure. Now it starts, runs, and drives with very little backfiring, and I even raced the engine a few times and it held through the revs and didn't backfire like it was.