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Weber DGV to Hitachi and A/C


josh817

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Getting tired of my balls dripping sweat in the heat. It's time to graduate. I'd like to know about the involvement of putting a '78 Hitachi carb onto my truck.

 

I'm hearing that the Hitachi for that year was a little bigger than a 32/36 (bought mine from someone who had it on a 1200), hopefully some better performance.

 

I have a '71 521 with an L20B and a L16 intake manifold. I rewired the car which is why I am asking what all is involved. I know there is an electric choke, BCDD valve, anti-dieseling valve, and possibly a fast idle.

 

If at all possible I would like to:

  • remove anti-dieseling valve (looks easy enough to remove needle or plug hole)
  • go to manual choke
  • improve fuel economy with BCDD valve? I try not to engine brake currently because I know at high RPM and a closed throttle plate I'm blowing out a lot of unburned fuel. In my 240z with triple Webers and no PCV setup it would shoot flames out the back and stink.
  • Utilize the fast idle solenoid for A/C

 

So I know at bare minimum if I can't rid the electric choke I can hook up a switched 12v easy. For the BCDD valve do I have to use the tranny/gas pedal switches?

 

 

As for A/C I am thinking about piecing a system together. I don't know how much hoses cost but everything here should be around $600-700.

http://www.summitracing.com/parts/vta-672001vhy/overview/

 

http://www.summitracing.com/parts/fss-58551/overview/

 

Driers and condensors are cheap, less than $150 total. My DGV has been dead reliable (but slow and best economy has been 20-25mpg) so worst case scenario I grab an idle solenoid and hook it to the AC clutch. I have a good looking Hitachi on the shelf though and I would like to try it one weekend if it doesn't require too many changes.

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It is worth reading the "Dime Quarterly" articles on Hitachi and Weber carbs http://dimequarterly.blogspot.com/p/back-issues-ordering.html  Go to Volume 1, Issue 3 and Volume 2, Issue 1. I haven't read these in awhile, but as I recall, the author said there isn't a huge difference between the Hitachi 340 and the Weber 32/36. How clean a particular carb might be is probably the most important thing.

 

If you go with the Hitachi, I would recommend hooking up the anti-dieseling solenoid. I don't have mine hooked up and it diesels like mad whenever the engine is turned off if at normal operating temp. In hot Texas summers it isn't going to be any better. One of these days I'll get tired enough of killing the engine with the clutch and run a switched 12V wire to the solenoid. If you want the solenoid to not work, unscrew it and remove the needle and spring, then reinstall the solenoid. If the needle and spring are installed and you don't have 12V to it, it kills fuel to the idle circuit.

 

I like electric chokes myself. If clean and adjusted right they work fine and it is one less thing to mess with. But manual chokes work fine too. I'd spend the time needed to convert to a manual choke in working on the AC project, since that is going to be somewhat involved.

 

The BCDD is a mystery to me. I can't recall if I have mine unhooked or have a vacuum line to it or what. It never seemed worth the trouble to remove it and fab a blanking plate. It always seemed easier to leave it on the carb and just ignore it One advantage of a Weber is it doesn't have a BCDD hanging off the side.

 

I'm all in favor of adding AC, considering where you live. I don't know what you are using for a radiator and fan, but adding AC will add a load to your cooling system, so you may need to go to an aluminum radiator and an electric engine fan. You need room in front of the radiator for the AC condenser and room for the electric fan if the stock belt driven fan isn't enough to do the job. If you drive in traffic a lot an electric fan may be more necessary. I would have a good quality temp gauge installed to monitor engine temp if you try going with stock radiator and fan.

 

Len

 

 

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Good point on the antidieseling solenoid, I read something similar to what you said. When I wire up my cars and add new things I make sure I don't put myself into a failure mode. Requiring 12v to get to a working solenoid seems that way... Broken connection or a solenoid that doesn't function one day can make you late for a meeting or strand you. Now that I see how easy it operates though I wouldn't mind hooking it up, especially if it is necesary.

 

How long does the choke stay on when heating? I currently don't have manifold heat so I know in the winter I have to run the choke forever but in the summer I don't use the choke at all.

 

The BCDD valve has me confused as well. I know when you're off throttle and coasting, I take that as engine braking, it lets air bleed into the manifold. My initial thought was this is good because that tremendous vacuum will typically suck a lot of fuel from your idle circuit and smell like gas or blow flames out the back. Basically it guzzles gas. It did that on my 240Z so I constantly popped it out of gear. At the same time I didn't have a PCV line to my manifold on the 240 like I do on the truck. I don't notice the stink on the truck like I did the 240 so I don't know if the truck guzzle gas just as much when engine braking or if that vacuum is relieved by drawing from the crankcase.

 

The thing with the BCDD valve is that in the description they also say they introduce fuel and by introducing air and fuel this somehow reduces emissions. I'm probably wrong to assume that reduced emissions = better fuel economy in this situation (engine braking). In some descriptions they say after '78 the tranny switches aren't needed to switch the valve off or something. That's where I get confused.

 

 

Lastly and more importantly. My truck is slow as bricks. I have a stock rebuilt L20B. I feel like its the carb and if its easy to switch to a Hitachi then I would like to try. I have a connection block on the firewall for all switched 12v sources, another for constant 12v, another for grounds. It's easy to run a line from the terminal to the choke or anti dieseling solenoid.

 

One thing is certain though... my DGV has NEVER failed me. Always starts, never had a problem with anything on it. Needs to stay that way as this vehicle is my daily.

 

 

 

PS: For what it's worth my truck had an old York compressor with a condenser in front of the radiator. There is a ton of space in the grill area. I had the under dash unit and tore it out (sold in broken pieces for $100) before I knew it was actually worth something, the vents atleast. This Vintage Air unit is similar, the AC and heat are separate. Only on this one the vents will be under the glove box instead of routing down the dash towards the driver side. This won't bother me.

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If you go with the Hitachi, you can always remove the needle and spring from the anti-dieseling solenoid and see if your engine diesels. But I would be more inclined to hook the solenoid up to switched 12V so it is working and keep in mind if the solenoid ever fails, then you can remove the needle and spring. It might be worth checking to be sure your carb still has the needle and spring in there. Someone may have already yanked them out.

 

I don't know the actual time for the auto choke to come off. If it is set right, I think it is about when the engine starts to get warm. That is another thing you can hook up and see if it works okay for you. If not, then you could go with a manual choke.

 

I looked at my BCDD and both the electric wire and vacuum post are unhooked. The engine runs and idles fine, but maybe it would somehow be better with the BCDD functioning. I suspect it won't make any noticeable difference in mileage or performance, but can't say for sure since mine has never been hooked up.

 

Unless there is something really wrong with your 32/36 Weber (and there may be. You may need to clean it and put in a carb kit), I suspect you won't see much performance gain from going with a Hitachi. For performance, either a 38/38 Weber or SUs is usually the drug of choice, but involves $$$. Make sure everything else is good - ignition timing, valves adjusted, new NKG plugs. Is your exhaust fairly free-flow? Small diameter pipe will put a drag on performance.

 

York compressors are great, although bulky and heavy. If you still have the York bracket it would make for an easy install. I don't know if it would be easy to modify the York bracket for a rotary compressor. It might be easier to build one from scratch. I don't know when Nissan started with rotary compressors on L-series engines. My '79 200SX still has a York. The Z20/Z22 blocks from the early '80s are supposed to be close to the same as L-series blocks, but I don't know if the bolt holes are in the same location on both blocks. If they are you might find  a rotary compressor bracket from an '80s Nissan that would fit your L block. I looked at a Z20 engine I have in my pile of parts and it looks like there are holes on the driver's side of the block which may be for a compressor mount.

 

If the under-dash unit doesn't direct the airflow enough to the driver's side of the cab, you can do a home made air deflector to redirect the cold air. But that may stick out too far if anybody ever rides with you.

 

If you do add AC to your truck, consider taking lots of pics and doing a project thread. It would be good info for everyone else.

 

Len

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The question I have is the Hitachi being from a 1200 is it jets capable of powering a L20B?

 

I would locate a carburetor off an L20B to start with.

 

As far as the electric choke and anti dieseling solenoid I would keep them they and be run from the same wire.

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My mistake, the Weber DGV I bought was from a user on here and he had it on a 1200 or 1300, whatever the 521 had before the 1600.

 

 

I have the Hitachi from the L16 as well as the L20B.

 

The York compressor bracket I don't think will work as it mounted like a lawnmower engine with the bolts on the bottom.. The compressor I linked is an Sanden SD508 which apparently is super common and looks similar to the 280Z rotary compressor. I'm sure I can steal the gear from a 280ZX.

 

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If your Weber was on a smaller engine, it is worth taking the top off and looking at what jets it has. At least I think the Weber jets have numbers on them and you can tell what they are without removing them. The DQ articles I linked to should tell you about what jets work well with a stock L20b. Also worth looking at the numbers stamped into the side of the carb base to be sure it is a 32/36 and not a smaller Weber. Finally be sure the carb linkage is adjusted so the primary and secondary butterflies fully open when the gas pedal is floored. You can check this with the engine turned off.

 

The stock L16 Hitachi was a 328 which is smaller than a 32/36 Weber. The '78 Hitachi you mentioned would be a 340 which is more or less the same size as a 32/36.

 

The Weber will be on an adapter plate to fit the Datsun intake manifold. After you remove the adapter so the Hitachi will fit, you need to install the correct thread and length studs to bolt down the Hitachi. Another reason to stick with the Weber unless there is something seriously wrong  with it.

 

It seems possible a 280Z or ZX AC compressor bracket might fit an L20b block. Hopefully without much modification. Do you have a dual belt crank shaft pulley on your L20b? Maybe all L20b crank pulleys were dual sheave.

 

You likely know this but I'll mention it anyway - When you get your AC system all plumbed together, it will need to be hooked up to a vacuum pump and vacuumed out. If you don't have access to a pump, you may need to take it to an AC service shop and have them vacuum and add the Freon (or whatever it is called now. Since "real" Freon was banned there have been a few different names on the market. R134 may be thing now, or maybe it is obsolete too). But being in Texas you probably know lots about the care and feeding of AC.

 

Len

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Thanks for all the info. I had made all these revisions when I first built the truck. L16 manifold, had the adapter plate, put in new studs.

 

From what I am told they utilize the mounts on the drivers side of the block. I do have a double row pulley, I have access to plenty of tools so installation won't be a problem as long as all my ducks are in a row so I can bang it out over a Fri-Sun which is why I am asking now so I can prepare. The only thing I can't do is the vacuum and charge A/C, or crimp hoses. I can put everything in and then go have a shop make hoses and juice her up. I have to check my stash of goodies to see if I still have the idler for the belt but again.... 280Z

 

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So the good news is that I found a belt tensioner in my stash. I can pick up 280 AC mounts on ebay pretty cheap or check the junk yard. Looks like this idler mounted on the front cover by the distributor. I kind of want one of these adjusters for my alternator...

 

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