1984 Nissan/ Datsun 2.4 (California)

[Big_Nachote]

Hey peeps, new to the 720 scene so I have a few questions. Currently have a 1984 King Cab 4x4 (2.4 motor). So I purchased this truck over a year ago, did not run when purchased (carburetor issues). After a year in the shop, i finally got it back running. I know a year is too long, that’s another story. Anyways the speedometer semi works.. starts at 35mph when idle so essentially zero. I’ve managed to drive past a speed radar and 70 mph on the speedometer equates to 35 mph in real speed. Is this a common issues or would a new speedometer cable fix this? This issue ties back into the carburetor issue. Truck runs fine inside city/ town limits but when on highway leaves me second guessing it. Feels extremely slow, even when going on the slow lane. I understand it does not pick up speed quickly but it feels like it doesn’t pick up speed past a certain point which makes me feel it’s unsafe to drive on the highway? Currently running a stock carburetor if that helps. 

[datzenmike]

Won't be the cable if reading 35 when stopped. The problem is in the gauge, you might take it apart and find the problem or just get one from an '83-'86.5 truck.

 

Sluggishness is hard to find a cause on a 720 as they are somewhat slow to begin with but it should reach highway speeds and well above. What did the shop do to it? What do you know about fixing your truck or does it always go back to the shop???

 

Check that the exhaust and the intake side plugs are both firing

Set valve lash 0.012" hot on both intake and exhaust

Ignition timing is 3 degrees BTDC in California

Compression of 150 or higher is good

 

The Z24 is notorious for blowing head gaskets every 100k. If you are always adding coolant or the exhaust is steamy when warmed up this might be the case. The preventative (before it happens) is to loosen one head bolt and tighten to 60 ft lbs. Then move to the next bolt. One at a time! On a cold engine and any order you like. Borrow a torque wrench and do it yourself.

[NC85ST]

Download a speedometer app to your phone and see how fast you’re really going. Depends a little bit on what you are used to driving as to how slow a 720 is. Also noticed that it’s a 4wd, slower still. Are you running oversized tires? 

[720_Jeff]

Stock tires were likely 215/75R15.

[Big_Nachote]

The shop only worked on rebuilding the carburetor and adjusting to getting it in running condition. Once they took it on they realized they weren’t as familiar with carbs as they thought they were(hence why it took a year to return). Unfortunately the truck went into the shop the moment I bought it since it didn’t run. I had it towed there. I’ve had truck in my possession maybe the last month and I personally have not done any work with it. I’m not a mechanic or anything close to it but with guidance or videos, I’m usually able to have an idea of what I’m attempting. 
 

Previous owner said it ran a Webber 32/36 before he took ownership (I currently have that webber but mechanics weren’t able to get that one going). Owner who I bought it from said he took webber off since it wouldn’t pass smog once he took ownership of it but that it previously ran good with the Webber before he bought it. 
 

Tires it currently has are LT235/75R15. 
 

Now that I have my truck back, I will have to keep an eye out on things you guys have mentioned and see if any of that helps or see if it leaks coolant, etc 

[datzenmike]

The lesson here is that you know just as much as those mechanics did. Better and cheaper to learn and do your own work.

 

215/75R15s are 27.7" diameter.

235/75R15s are 28.8" diameter.

 

With 235/75R15s on at 100 MPH you will be reading 96.18 MPH or roughly 4% faster than what you are reading. At 50 MPH you read 48 MPH. At 25 MPH you read 24 MPH

[bottomwatcher]

Not going past a certain speed is usually a clogged fuel filter. The truck just keeps getting slower and slower.

[Big_Nachote]

Sorry for the late reply. Hopefully I still get some feedback. I was able to top the 720 at 64 mph according to Waze App but realistically it was more of a consistent 60mph. I have re-torqued the head bolts to 60 ft lbs. The truck has a new fuel filter about a month old. 
 

I’ll have some free time tomorrow and looking to valve and adjust and possibly compression test.. 

 

On the valve adjustment.. do I only need to set intake and exhaust spark plugs to 0.012 or is it all of all them?

*Also what spark plug numbers are the ones associated to intake and exhaust?

[datzenmike]

Valve adjustment is for the valves and has nothing to do with spark plugs. Do you have a factory service manual? It will show you where and how to adjust them.

 

 

Z24 spark plugs are

 

Intake side...... NGK BPR6ES set to 0.31" to 0.35" gap

Exhaust side... NGK BPR5ES set to 0.31" to 0.35" gap

 

Top speed should be close to 80 MPH at least. There are several things to look at yet but get the valve clearances checked.

[Big_Nachote]

Sorry as mentioned earlier. I’m novice when it comes to mechanics but can get by.. I’ve seen videos on how to set valve adjustments and must have misunderstood.

but you previously mentioned to set valve lash to 0.012 hot on both “intake and exhaust”.. I guess this is the part confusing me..

what do you by setting valve lash to intake and exhaust? Do I not set valve lash to all?

[datzenmike]

The valve clearance on the intake valves is 0.12"

The valve clearance on the exhaust valves is 0.012"

So set the valve lash on the intake and the exhaust valves to 0.012". All 8 of them.

[Big_Nachote]

Sorry still a bit confused and hopefully I am not coming off as a smart ass or jerk. But from the way I understand your last sentence paragraph.. 

 

“The valve clearance on the intake valves is 0.12"

“The valve clearance on the exhaust valves is 0.012"

*Doesn’t that make this sentence contradicting? - So set the valve lash on the intake and the exhaust valves to 0.012". All 8 of them.”

 

Really not trying to be a smart ass, what I’m asking is for a way to simple it down more or make it make sense to a novice please 

[datzenmike]

No no, it's just a misunderstanding. All valve clearances are 0.012". There are one intake and one exhaust valve per cylinder, 4 of each and 8 valves in total. All need to be adjusted to 0.012" clearance. This clearance assures that the valve fully closes and seals. The valves are cooled by heat transfer to the seats when closed so it's important they close fully.

[Mechano]

On 6/14/2023 at 11:51 PM, Big_Nachote said:

did not run when purchased (carburetor issues).

 

Some excellent advice has already been posted and most of the bases covered, but  there is another *potential* cause that should be considered considering the known history of the vehicle

 

When a catalytic convertor equipped vehicle has fueling issues, it can often overheat the catalyst, causing internal damage.

This is because running incorrect fuel mixtures can melt the internal honeycomb/matrix of the convertor which can obstruct exhaust flow

This can lead to lackluster performance under load like you are describing

 

A test of the manifold vacuum under load with a vacuum gauge might be a usefull diagnostic step ?

 

Just a thought from an old guy who got his ass kicked by this in the past

[datzenmike]

Ruling out the easy cheap stuff first. It's a good point.

 

Other lack luster performance...

 

Secondary not opening.

Exhaust side plugs not firing

Incorrect ignition timing.

 

[Big_Nachote]

I was finally able to do the valve adjustment. I also changed out all old spark plugs and installed new ones BRP6ES and BPR5ES. And the truck seems to be running a whole lot better now. I was able to reach 75mph and easily 70mph which is plenty for a highway speeds. 
i did notice when replacing the spark plugs that both spark plugs on cylinder 1 were almost closed (not anywhere near the .32 gap). So that’ll be something I’ll keep an eye on to see if they’re closing from malfunction or if previous owner didn’t gap correctly.

[datzenmike]

Perhaps an extended tip? Those would be wrong. Another cause of tip damage is a foreign object getting in there. Worse case is a piece of piston.

[Crashtd420]

On 6/27/2023 at 12:27 AM, datzenmike said:

Z24 spark plugs are

 

Intake side...... NGK BPR6ES set to 0.31" to 0.35" gap

Exhaust side... NGK BPR5ES set to 0.31" to 0.35" gap

 

 

16 hours ago, datzenmike said:

Perhaps an extended tip? Those would be wrong. 

This kind of contradicts the BPR recommendation... the P stand for projected tip so how could that be wrong.... plus wouldn't that happen to all cylinders if they were wrong....

 

[datzenmike]

P... oh yeah. Champion may be more projected? Also plugs aer at an angle to the piston, depends on the plug index it may be turned so the piston is on the far side of the ground strap.

[Big_Nachote]

Back with more issues guys. After changing spark plugs the truck ran fine for a few days. Hadn’t driven it much since then. During spark plug change, some of the old spark plug wires got damaged but were able to be put back on and seemed to work. I was bringing the truck home today from my parents house and stopped by AutoZone for electrical cleaner and was also going to change those old spark plug wires and when I came back out from the store the truck wouldn’t stay running anymore. It starts up but will not stay running unless I have my foot on the gas. Could these be a result from faulty spark plug wires? Any ideas or suggestions. AutoZone didn’t even offer to help by the way 

[datzenmike]

As you say you damaged them, yes probably the cause. Get NGK wires if possible. 

 

[Big_Nachote]

I don’t think the spark plugs were it. Just replaced them at AutoZone with NGK ones and still no luck 

[datzenmike]

That's why I said...

 

44 minutes ago, datzenmike said:

As you say you damaged them, yes probably the cause. Get NGK wires if possible. 

 

 

[Big_Nachote]

Sorry meant to say the spark plug wires. Just replaced the wires maybe about 10 minutes ago. Spark plugs were done about a week ago. 
 

[NC85ST]

It sounds like it has trash in the idle circuit of the carburetor. In your original post, you said that it hadn’t run in about a year and that it was having problems before that. So it’s possible that it hasn’t run in quite some time. If that’s the case, it’s possible there’s a lot of junk in the gas tank and some of that is getting past the fuel filter. You might end up having to take the tank out and cleaning it.