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MikelB

My Nissan 720

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I have an almost perfect Nissan 720 pickup with a z24 engine in it, 4x4 five speed. It only has 40,000 original miles on it and over all is in pretty good shape after sitting parked in a field for 20 plus years. 

The one problem I'm having is that it doesn't seem to have very much power or speed. I live in Montana where the speed limit is 80mph and i drive back in forth from here to Portland, Oregon a couple times a year and its frustrating when my top speed is 65mph. Im wondering if there is anything I can do to get more power and speed? 

Im very new to working on vehicles and so please be as descriptive as possible, Id appreciate it very much. 

I should also mention that I have a brand new weber carburetor in it along with a new radiator.   

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It's suspicious that anyone would park a 40K truck in a field. There must be some reason? perhaps the lack of power?

 

Off the top of my head... check for spark on both the intake and the exhaust sides. Not at the coil but on one of their plug wires. If one side is missing this will give poor performance and crappy mileage. You should get up into the 20s with a 4x4.

 

Just pull a plug wire off and stick an old plug (any plug even a lawnmower) in the end and lay on a grounded surface. Turn engine over with starter.

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So I was told these trucks have a lot of wiring issues would that be something to do with it? I will check for spark, I don't know if that will be it cause I get really good milage. But definitely worth checking. 

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Electrical is pretty good but being over 40, previous owners tend to add things like CB, stereo, fog lights and take short cuts fixing things. Keep in mind that this is an older vehicle that wasn't that fast or powerful to begin with. What is your mileage? Good would be 22-24. Mixed is about 17 and under, again for a 4x4.

 

Good mileage is a good indication of engine condition. Lack of top end is troubling. Where did you get the Weber from as there are fake knock-offs from China. A 32/36 should wake the Z24 up. At 40K it's well over due for a tune up and if you haven't done one you never know what or when it was last done.

 

Valve lash is 0.012" in and Ex on a hot engine.

Timing 3 degrees BTDC + - 2 degrees

 

All differentials, (GL-5) transfer case and the transmission fluids (GL-4) are due for replacement at 30K intervals.

 

Engine oils are constantly being re-formulated and the zinc (ZDDP) levels dropped to about half what they used to be. This is because all engines today don't need it on their roller rocker cams and the zinc messes the new catalytic converters. To err on the side of caution I recommend a light weight diesel engine oil like Shell Rotella T4 or Chevron Dello 400. I'm running 15W40 but it's warmer here and I only drive in the summer. You can also get ZDDP additive packages for your usual oil or pretty much anything marked 'Racing oil' like (but not restricted to) Valvoline VR-1. I would not recommend a synthetic as this is totally over priced for protection that is never going to be needed and synthetic tends to leak past old gaskets and seals. I would urge you to look up the ZDDP controversy as it relates to older 'flat tappet' type engines like ours, become informed, and make your own decision. 

 

I suspect this cam lobe wear is a result of today's lower ZDDP levels...

AlI8XOe.jpg

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65mph is probably it and still get good mileage, if you want to go faster your going to have to put your foot deep into the pedal and your mileage is going to drop/suffer.

It is a 4wd so the gearing is not likely freeway oriented, and the Z24 is not a revving type of engine, and I am not sure if it is possible to put better more freeway friendly gearing in it as you have 2 gearsets in it(front/rear) and they need to match, there are others on here that know more about that stuff.

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What wayno said. If the mileage is good... call it good. With 4.11 gears and in 5th you're  at 3,000 RPMs. Peak torque is @ 2,800 so good right there. 

 

 

It should go faster that 65 though. Are you saying that when floored it won't go over 65??? That wouldn't be right.

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Don't think the mileage in my 84 720 4x4  is too hot, but I do know the carb needs to be replaced, leaking at butterfly shaft ends. But I do get 100kph in fourth at around 3800 rpm and there is still 5th gear.

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Fuel filter is #1 issue for not reaching full speed. Truck sat will need frequent changes for a while. Good news is filters are cheap and easy to change 

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Yeah, part blocked filter will limit top speeds possibly float level set too low also. A part blocked filter will also cause the engine to quit climbing steep hills at a lower speed and top speed would be lower on windy days.

 

19 minutes ago, weldingrod said:

 But I do get 100kph in fourth at around 3800 rpm and there is still 5th gear.

 

Tach should be reading  3,250 in 4th at 100k. Based on the '85 4x4  4.11 diff and 25.5" diameter 195/75R14 tires.

 

If tach is correct then your speedometer is out and should be reading 70MPH or 112.6 KPH

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Ive replaced the fuel filter once when I first started driving the truck about 8 months ago. 

I have a brand new Weber Carb. . . And paid a professional to tune it up.

I replaced all the liquids in the truck when I first got it. 

I do have an exhaust leak, i'm replacing all the exhaust this week and will do the fuel filter while i'm at it and see what happens. 

Can I post picture on here somehow? 

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20 years of sitting plus modern Ethanol that is actually really effective at cleaning the whole system, that filter will clog frequently. I change mine annually on a clean running truck. These are nothing like modern vehicles with check engine lights and codes. They need constant maintenance of fluids and filters, cheap and reliable if you put in the effort on maintenance otherwise you will have frequent breakdowns and disappointment.

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Just keep up the regular maintenance and you're ok. Datsuns are quite forgiving. If your Datsun lets you down there's one thing that you can do that you can't on newer cars. 95% of the time with just a few tools (what Datsun owner drives without some?) and a piece of wire you can fix it and at least limp home. The other 5% of the time you 100% know what's wrong. Try that with a new car that you can't even check the transmission oil on...

 

 

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I have an all new exhaust system and seems to have helped a lot, fuel filter will be next as soon as it stops snowing here 

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My next concern with the truck is that the steering column makes a squeaking noise,  I don't know for sure that it's the steering column but I don't know what else it could be. I tried putting a dry lubricant on it to see if it was just plastic rubbing together but that didn't seem to help at all. Do you guys have any other suggestions? 

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I am going to sleep now I will check back tomorrow evening.

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