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z20s carb


midtown720

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My truck is a 83 nissan 720 base model. Its very possible that l20 weber carb could fit. I just want to make it up hills better lol. I get very good gas mileage but I need more power. I can drive 65 down one side but I'm barely doing 45 by the time I'm at the top of the hill. It has very little pull up any incline.

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The Z20 in the 720 is also known as the Mileage Option engine. All Z20s are small two liter engines, only came with 5 speeds, they have a ridiculous 3.364 differential and the compression is 9 to one with a knock sensor and ignition retard (no kidding). This makes for good mileage but poor performance.

 

I don't think a weber is going to really give you what you want which is to go up a hill without down shifting and way more acceleration through all the gears. I say this because of that 3.364 differential. I would search the junk yards for a 720 with a 3.889 diff and swap it in. If it has a 5 speed, get the speedometer drive pinion as well and swap it into your transmission and the speedometer will still be accurate. Going from 3.364 to 3.889 is a 15.6% increase in engine RPM across the board in all gears.

 

Generally, an engine makes more power the higher it revs up. Your truck with 3.889 gears at the same speed as your old differential will be revved up 15% higher making more power and accelerating harder. Warn you now... gas mileage will suffer. 

 

A new weber (and I mean a new replacement one with everything needed including the gaskets, adapter, bolts, air filter and more) is almost $300. You should be able to get a rear diff for $50-$80... maybe less. $5 for gasket sealer and $15 for new GL-5 oil. I heartily recommend a gear change and later replace the carb if you like, but I'm sure the gears will surprise you.

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It's a 4.11 but it's a C-200. You need an H-190 it's in all the 2 wd trucks.

 

 

It should rev higher and stronger than that. Ask around or search a few 720 builds for info on checking your hoses and emissions equipment. The emissions equipment do not harm performance but if they are neglected or poorly looked after (loose or leaky hoses, disconnected things)  they can. Get everything working properly and you should see a difference.

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It will be a good project this weekend. I appreciate the help. Its my $700 dollar trash and work truck. I didnt like it at first but I couldn't think off getting rid of it now. I did some adjusting to the carb because the manifold was glowing hot after coming up a hill that's near my house. I read on line and it said it wad running lean?

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Bear with me for a minute.

 

Take both coil wires off and put a plug in the end, lay on a grounded surface and use the starter to crank the engine. Do you have spark on both coils??? If one is not sparking replace the first fuse on the far right of the fuse box and re-test..

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It will be a good project this weekend. I appreciate the help. Its my $700 dollar trash and work truck. I didnt like it at first but I couldn't think off getting rid of it now. I did some adjusting to the carb because the manifold was glowing hot after coming up a hill that's near my house. I read on line and it said it wad running lean?

If you floor something long enough, it's going to get the exhaust manifold hot, REALLY HOT!

I have a few Datsun diesels, I put an exhaust gas temperature(EGT) sensor in one of the non turbo engines I have, and drove it around for a while, up hills and such as I wanted to know the difference between turbo and non turbo engine exhaust gas temperatures(EGTs), what I found out was that even normal engines will get to 1400 degrees going up just a regular hill that one doesn't even need to downshift if floored long enough, now if the engine is small and doesn't have a lot of power, you will be floored, that is when the temps rise the fastest, and it takes less than a mile.

If you are over 1400 degrees for a long time, it can start to melt stuff, so if your exhaust manifold is glowing orange at night after going up your hill, maybe you should go up the hill slower, otherwise you are going to be shopping for an engine one of these days, I suspect you would like a Z24, they have grunt/torque.

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When I first noticed the hot manifold I then looked up different videos on what it could be I cane across some info on it being lean. I then adjusted the carb for a richer mixture and the glow has went away. I dont open the throttle fully on the hills because I'm afraid it will flood out even it hasn't since I've had it. It seems it responses better to 3/4 throttle better. Full throttle seemes it kinda holds back in a way.

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  • 2 weeks later...

The neg cable bolts to the intake near the thermostat. There may be a braided ground wire from the back valve cover bolt to the firewall.

 

As mentioned adjusting the mixture on the stock carb only alters the idle and couldn't have stopped the glowing manifold. Does your carb have a small round glass window on the front?

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I'm new to the forum and I can always find out what I need through a quick search but I can't find where I can get a weber carb for my z20s. I see webers for the z22 and z24 but not my motor. Do I need a l20 weber or are z24 okay? Thank for the help

 

Greetings.

 

I have a similar question. I  have a 720 ('83) with a Z20, acquired a few months ago. The truck has been doing what I need for it to do (28 mpg doing light hauling without many hills to climb), but it diesels on shutdown and has taken to idling at around 2100 rpm.

 

To make a long story short, after determining that the problem wasn't (just) aged and leaky vacuum lines, I bought a carb rebuild kit and following the Lugnutz excellent tutorial, began tearing it down.

 

This carb has been worked on before, and several small parts have gone missing. In particular,  the screw and brass cap for the throttle shafts is missing, and there are no rubber seals. Might explain the high idle. The anti-dieseling solenoid has a broken spring, and the needle looks very worn. Could explain the dieseling. The accelerator pump lever has no bushing, but it has been bent in such a way as to work okay anyhow. Etc.

 

Oh, and it turns out that the air cleaner is held on to the carb by a nut that isn't a wingnut and isn't quite the right size, and no bolts to the crank case cover...

 

So it seems that my options are to try a significantly more extensive repair, buy a rebuilt carb or buy a Weber. 

 

All things considered, repair is not my preferred option. I need a working truck more than I need a new hobby.

 

What are the pros and cons of a rebuilt vs. a Weber? Taking into consideration that I like good mileage and don't need more acceleration/hill-climbing power than I have now. What's a good source for a rebuilt? Is a Weber even an option? I've read that the carb on the Z20's of this vintage is the same as carb on the Z24's. But does that actually imply that a Weber replacement for a Z24 would work, or work well? It would be nice to step past the air cleaner issues, too...

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  • 2 weeks later...

...no, but you can get close by setting the crank to the compression stroke on #1 cylinder and carefully turn it clockwise up to the 3 degree timing mark on the scale. Have a spare spark plug in the #1 plug wire and well grounded and near the distributor. Loosen the distributor so it can be rotated. Turn the key on and rotate the distributor back and forth through it's advance-retard range. You should be able to hear the snap of the spark jumping the plug gap. Note at what position the distributor is facing when the sound occurs. Do this multiple times to narrow it down. Set the distributor there and tighten it down. It's not perfect but more than enough to get it running and drivable.

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