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How to fix Stock Hitachi Carb


DatDoug

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First take off big huge ugly-ass air cleaner & throw away. Unbolt stock carb undo linkage, fuel line & wiring. Throw carb as far as you can into bushes, lake, trash, basically whatevr is around you. Bolt on Weber carb. hook-up fuel line, linkage, wiring & vaccum line. Your done!

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Yes, DatDoug, throw that Hitachi carb with worn out, air sucking throttle shaft bores in the woods, or sell it to an unsuspecting dummie like stevensonDNL so he can try to get it working on his truck with unadjustable, erratic idle, until he takes it off and throws it in the woods. Maybe then stevensonDNL will come to his senses and fork out the cash for a Weber 32/36. But seriously, why hasn't anybody come up with a kit to ream out the bores and install bushings in the Hitachi throttle bodies? You can buy bushing kits for Rochester Quadrajet and other carbs. I don't regret buying those two Hitachis from you DatDoug, as I've been having alot of fun learning how they work (and don't work) when they get worn out.

 

Dan

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You guys.

 

Nothing wrong with the Hitachi carbs. They work great. However you would act up too if you were 35-40 years old and had traveled 100+ thousand miles. Assuming in that time some PO hasn't swapped some other model carb (or parts) on or botched a re-build. By then things are worn out that a re-build kit may not fix, assuming someone does the job right. So yeah throwing it away is often the only course. The original Hitachi was balanced to give good mileage and performance while remaining within the emission levels of that year.

 

If the Weber had been on the car that long and you put a new Hitachi on you'd be throwing the Weber away.

 

 

If you had a brand new Weber and a brand new Hitachi and compared them the difference would not be that great. The Weber flows more air so will perform slightly better than the Hitachi I agree.

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I agree the stock Hitachi are pretty good carbs. Just like any carb, given clean air, and clean gas, without water in it, they work very good for a very long time.

It is a much more sophisticated carb that the Weber, more sophisticated than the Quadrajets, or Carter carbs.

Because of its sophistication, it is harder to diagnose, and to get to run properly. Webers are easy to tune, because they are fairly simple.

 

Now for the availability of throttle shaft repair bushings. There are probably 20 or 30 domestic carbs needing them for every one Datsun carb, and how many people would actually repair them? It is not good business sense to try to sell something with such a limited market.

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That's the way I felt too when I replace my Hitachi with a Weber. It has been completely trouble free so far. But, I always suspected that a comparable Hitachi (in new condition) would get better mileage. Has anyone ever tested this to see which one generally gets better mileage? I've heard a few people say the weber does better, but I don't know if they had anything to back it up.

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It would be really hard to compare the mileage, because one of the critical adjustments is the float level. Adjust the Hitachi float a little too high, and the Weber just might get better mileage.

I believe Carbs get blamed of a lot of issues, that are caused by other engine conditions. Valves good? Ignition good? Rings good?

You have to check all the other stuff before you start tweaking the carb.

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I believe Carbs get blamed of a lot of issues, that are caused by other engine conditions. Valves good? Ignition good? Rings good?

You have to check all the other stuff before you start tweaking the carb.

That's for sure. Generally, you mess with the carb -AFTER- you've verified everything else is correct.

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  • 3 weeks later...

the\ stock hitachi does its job but not very well mine literally fell apart from the linkage pushing on it and i had a huge vacume leak with that being said this write up is justified think about it where are you going to get a brand new stock hitachi? your not you can get a weber brand new all day long not to mention the much simpler (and superior) design i seriously want to know what possesed the engineers at hitachi to think a vacume secondary was a good idea the diaphram ripped and it was all done i cant stand hitachis if i got a brand new one that would be different but since its impossible weber all the way

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Vacuum secondaries do not open until the engine RPM is high enough to pull enough air through the carb to atomize and vaporize the fuel going into the engine. This is a much more precise way to measure fuel.

Mechanical secondaries can be opened immediately, at engine idle, and this often creates a lean bog, that is just covered up by dumping extra gas down into the manifold. This is why many 4 barrel Holley carbs are set up as double pumpers.

The requirements to accurately control engine fuel demands was greatly impacted by emission laws that started to be implemented around the time Datsuns were getting popular, and in the 1970's, Gas prices were going up dramatically, and this really helped to create a demand for small cars, that had good performance, and got good gas mileage.

Almost every V8 car and truck that had a four barrel carb from the factory had a vacuum operated secondary of some type.

At the time Datsun was putting two barrel carbs with secondaries on it, most American manufactures of cars were just using a single barrel carb on their four and six cylinder engines.

 

There is a lot of validity to your argument that it is hard to find a stock Datsun carb that does not have 40 years of wear on it. I am pretty sure Weber also makes vacuum secondary carbs.

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First take off big huge ugly-ass air cleaner & throw away. Unbolt stock carb undo linkage, fuel line & wiring. Throw carb as far as you can into bushes, lake, trash, basically whatevr is around you. Bolt on Weber carb. hook-up fuel line, linkage, wiring & vaccum line. Your done!

 

What about remove intake, install cannons with dual 44 mikuni's and air horns? :D Bet you can guess where my tax check is going!! :P

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the stock Hitachi does its job and very well, until it finally wears out. It is much better than the Weber 32/36, more sophisticated fuel metering results in better fuel economy and better emissions while maintaining driveability.

 

The Weber 32/36 is a good carb too, just not quite as good as the old Hitachis. Weber 32/36 is bigger, so it's not a perfect comparison.

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i swear the dch or dhc340 what ever the 340 hitachi is was faster on my l20b than my weber. not to mention a hell of alot quieter sounding with that big'ol air cleaner.

 

stupid fucking weber air cleaner housings pit and rust after a year or 2. not easy to find the old school aluminum ones.

 

lets not mention that you have to drill your carb mounting holes over 1/4 inch to fit it on the adapter which is supposed to be a direct bolt on. i know nobody knows what i'm talking about on that one for some reason.

 

yeah i bitch and then have webers on both my 521's :fu:

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  • 5 years later...

So I know this thread is 5 years old but it seems fitting to ask here. What wears out on a hitichi? I've been having the same problem with mine for the past year that it won't send any fuel through the idel circuit. I hear the anti dieseling solenoid open and close, rebiult the thing 2 times, cleaned every hole, messed with the mixture screw, and the b.c.d.d. (I think) valve setting and it still won't idle lower then 1600. It's on an l20b that sat for years. I've replaced all the vacuum lines and I know there are no leaks. I can't switch to a weber because I live in California and my 510 is a 78 so it gets smoged. Any ideas on what it could be? And where I can get a new old stock?

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Dirt, or dried up gasoline sludge somewhere can mess up the Hitachi carb.  There are a lot of places stuff can hide in one.  Passages can have more than one hole in and out in the carb body, so that may appear clean, but are not.

 

Having said that, the most common cause of a high idle speed is a vacuum leak.  

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i swear the dch or dhc340 what ever the 340 hitachi is was faster on my l20b than my weber. not to mention a hell of alot quieter sounding with that big'ol air cleaner.

Yes, DCH340 from L20B is larger than Weber 32/36. But if from L18 is just about same size.

 

If you jet the DCH to run as rich as the Weber, it will fly.

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Did you flip it over?

Don't know if you're making a joke or not. But Ya I soaked the thing and used about 5 cans of cleaner. I don't know where the leak would be. It won't run without fuel coming out of the primary. I tried a trick some chevy guy tought me of reving the engine up to 4k then suffocating it with a rag to clean out anything and it didn't do anything
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What leak? Idle passage not letting fuel into engine is not caused by a leak. And if no idle fuel the engine won't idle (run below ~1500 rpm).

 

Fix the blocked idle passage or replace the carb. I'd start with removing the anti-diesel valve and cleaning the passage there. Make sure fluid will go through. Then remove carb and and idle mixture screw and back-spray through the idle hole. If there is a right shape chunk of rust in the passage, you'll never clear it out. It happens sometimes.

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"I've never had an overrated Weber 32/36 run as good as a rebuilt Hitachi."

Bullshit-detector.jpg

You must have never tuned a Weber or adjusted timing once you put it on or you installed it improperly. My Hitachi was rebuilt (not by me but an old Datsun mechanic), and it ran like crap, especially when cold OR hot! Flooding at lights, backfired, wouldn't stay running in cold, Idled up and down, dieseled EVERY time I turned the truck off, etc. My Weber runs so smoothly, I swear it runs like a modern computer controlled fuel injected vehicle... no matter what the weather, makes more power and low end torque, AND gets better fuel mileage. Shitachi carbs suck! Not to mention they are a pain to tune and get parts for. Weber is so much easier to tune and rebuild AND parts are not only easy to find, but cheaper as well. Hitachi has a bad reputation because they deserve it. And these comments about somehow the CFM being more on the stock carb is insanity! And it sure as hell is not 230 or 270 CFM. The stock Hitachi is larger than that! It is minimum of 300, maximum of 330. With the Outlaw 38 being 380CFM. That is like going to the racetrack and convincing people to switch back to the factory (whatever) instead of the big CFM Holley carbs they are running! And a Weber does not "run rich" either. Forget California's weirdness, but they still have to be FEDERAL emissions compliant. But if you TRIED to get a Hitachi to run rich to beat the Weber, it would just run awful because that is not what it is designed to do. It is designed to be compliant for emission and fuel requirements for whatever year the vehicle was made, plus perform decent enough to keep the customers happy. It is not a designated performance carb like the Weber.

 

With that being said, I think Mike hit the nail on the head about replacing something old and worn out with something new. Mine was worn out to the point of no rebuilding was going to help. I went with an old junkyard (Genuine and old school) Weber and rebuilt it, jetted and tuned it to what I wanted so far as performance with the exhaust and air intake modifications I was making. But I am not running the silly stacked adapter plates but rather a 1.5" custom spacer from Trans Dapt. I am also not running the tiny Weber air filter, I am running a 10" round air cleaner to take advantage of the stock hood vents. I also ported and polished the intake manifold. All that work and extra parts and I still came out a lot cheaper than the kit from Redline I did my research and homework. I had even considered a Holley (not 5200) two barrel and custom intake manifold, yes it can be done! Even a Holley four barrel can be done. The L and Z series four cylinder four bangers have roots in circle track racing so nothing is impossible, if you have the money and resources. Heck, Ford's 2.3 Pinto motors and Toyota's 22RE is still being used.

 

 

With all that being said, I "fixed" my Shitachi carb like the OP said... Put on the Weber 32/36, then played golf with the Hitachi using a sledgehammer as a driver! To me that is the ONLY way to properly fix one! Junk it and replace it with a Weber or Mikuni. Besides, the Weber looks 100% better!

 

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