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Discussion Starter #1
I've been thinking about swapping my stock carb. 1985 720 4x4 with Z24. I've heard good about both the stock and Weber and wanted to gauge some current opinions. What do y'all have (stock, Weber, etc.), how long have you had it, has it impacted your power, fuel economy, etc. Any info would be a huge help. There's a K646 kit online for $300 even, includes a genuine electric choke Redline Weber, adapter plate, linkage kit, and air filter. Also thinking about an MSD ignition box. Any comments on that as well would be appreciated!
 

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NF Mod/Nissan Master Tech
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I'm a retired Nissan Master Tech and I started in Nissan in '86, so I'm been around a few of these engines. The stock Hitachi is a good carburetor and most of the problems that people have with them is because they aren't familiar with them. A lot of people and mechanics grew up working on Rochester's and Holley's, etc., but they Hitachi's are a little bit different. You don't mention if you are having any problems with it or not or if you are looking to upgrade the performance. If it's working well, leave it alone and save your money. If the factory carb is working well, there is no other carb that is going to make it run any better. The same goes for the ignition box. The factory system, as you know, already has a dual ignition system with 8-spark plugs and two coils; do you really think it needs any more spark than that? The Japanese know what they were doing when the built their engine backs then. The NAP-Z engines were really interesting in their design for their time. The NAP-Z engine was developed with Hitachi and was designed to facilitate a lot of EGR flow but still have good fuel mileage and power and it also has a Hemi-head. They were also durable. Occasionally, you might run into one with a blown head gasket between adjacent cylinders or run into one with an intake gasket leak, but they were about as solid as any engine around in its day. Unless you are going to full-bore, performance makeover, there's really no sense to go with anything else but stock parts.
 

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Discussion Starter #3
Awesome info! Much appreciated! A few questions if you don't mind.

I bought the truck a few months back, and the previous owner told me he had the carb and head rebuilt. At first it wasn't running the greatest (I assumed potential carb problem), but by doing a standard tune-up (plugs, wires, filters, fluids) it was improved. Is there a way to tell if it's an aftermarket carb or an original Hitachi? I honestly haven't looked.

In terms of fuel economy, I have been a bit disappointed. I'be heard some people getting up to 30 mpg on the Z24, but I average around 17-18 with regular gas (87), even less with premium (93), which is what I have to run or the engine pings/detonates. Do you have any advice on increasing fuel economy? Would removing all the emissions stuff help, in either performance or economy? If so, what needs to stay and what needs to be removed/plugged?
 

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Sup Mod keeping the peace
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The emission requirements of the state where the vehicle is registered determines how much leeway you have in removing emission related components. If the emission requirements are very lax, then you can remove the CAT or install a high flow CAT which might help; also disabling the EGR and installing a free flow muffler might help.
 

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NF Mod/Nissan Master Tech
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I'd leave the emission stuff alone, personally, especially the EGR and especially if you are "pinging" on regular gas. In fact, you may want to make sure the EGR is working just for that reason! There's no reason to replace the converter unless it's restricted; an exhaust back-pressure tester can tell you that, but you would likely feel a loss of power while you're driving if that's the case. It's still not a bad idea to have the back-pressure tested because if the cylinder head was rebuilt, it may have had a blown head gasket and the coolant could have ruined the converter. "Pinging" usually occurs when the timing is too far advanced or the combustion temperatures are too hot, which could be due to insufficient EGR, compression too high or mixture too lean. A compression test wouldn't be a bad idea to make sure they didn't shave too much off the head or got the timing a tooth off on the engine. Also, check your ignition timing and if you have the 8-spark plug engine, which I'm pretty sure you do, the timing light lead goes on the intake-side, #1 spark plug (not the exhaust side). Usually if the original Hitachi carb is on the engine, it'll have the original air cleaner on it, as it won't fit the webber carb. It'll also have a round, glass "window" on the side of the carb to check the float level; if the float is correctly adjusted, you will see the fuel level in the fuel bowl in the middle of the window. Hitachi carbs also typically have the Hitachi emblem on the top of the carb.
6091
 

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NF Mod/Nissan Master Tech
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BTW, if you need a factory service manual to help you, go to the "service manual" section at NICO Club's site and go to the "Datsun manuals" section. Look for "720." They have an online manual of the 1982 720 truck, which is close enough to the '85 manual for most purposes.
 
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