Hitachi DCH340 Carburetors: All Physically Interchangeable?

[Cardinal Grammeter]

I want to put my 74 620 L18 4-speed back to original with a DCH340 carb. 

 

There are many suffixes, do I need to get the precise one for it to fit properly?

 

or are the suffixes related to jetting and tuning?

 

I have the 73 and 74 Datsun Pickup Service Manuals and here are the listed suffixes:

 

1973 Models:
 

-1 L18 610 auto

-2 L18 610 man

-6 L16 510 auto

-7 L16 510 man

-8 L16 620 auto

-9 L16 620 man

 

1974 Models:

 

-10 710 man

-11 710 auto

-12 620 man

-13 620 auto

 

Notice that the lower suffix is the auto in 73 but the manual in 74 (!)

 

Mine is a 74 620 man so I would need the DCH340-12 but could I use any of the other ones?  The thing I really want to avoid is a version which would not connect to the throttle cable, air cleaner, etc. properly.

 

Thanks in advance,

Tom

[ggzilla]

Yes they are all physically interchangeable.

 

But emissions vary.

But throttle linkage can vary.

[datzenmike]

Truck L18 carbs on your list are cable operated. 510/610/710 are all linkage. Later L20B S10 (200sx) and A10 (later 510s) are cable. If using a truck or later car L20B carb the jet's would likely need to be changed to fit the smaller displacement L18.

[Cardinal Grammeter]

So are there just two physical types:  cable and linkage operated?

 

What about choke?  Are they all electric?

 

I'm assuming all 340 air cleaners are interchangeable?

[datzenmike]

Some L16s were man choke but L18 and L20B were all electric. With enough parts, linkage could be swapped to cable operated I imagine.

[Cardinal Grammeter]

I've been trying to find a good close up pic of the linkage at the carb installed - worst comes to worst and I could fab the the carb linkage.

 

Ironically, I'm interested in economy and what they have now is a 1-bbl with plastic cable tie connecting the carb linkage to the throttle cable that only gets about 50% throttle plate opening when gas pedal is floored!

 

I believe I did see some 340's which may have had different air horns:  some tall and some virtually flush with the carb.  For the stock aircleaner - or at least the ones that were in the bed when I bot this truck - look like they clamp onto the tall cylindrical type.  But need to check this more carefully...

[Cardinal Grammeter]

I also confirmed that some 340's have no extended airhorns like the Datsuns.  For these carbs, the OE air cleaner has nothing to clamp onto.

[Cardinal Grammeter]

Do all DCH340's have the same fittings on them such as fuel, water, vacuum, emissions, etc.

 

Do California variants have anything different?

 

I also need to find some kind of schematic that shows how the carb is plumbed since I have nothing to go by - mine was completely stripped.

[DanielC]

If you have a choice, I would get a DCH340-12, my second choice would be a DCH340-9, if they are the manual transmission versions.

The pickup version of the carb will have the cable throttle bell crank. or pulley.

Car versions have a twisting mechanical linkage. 

Automatic versions of the carb may have a dashpot, that will slow the return of the throttle to idle, that could be a problem when shifting.

[ggzilla]

Yes, there are variations with differing emissions features. Even in the same year, as many as six variations were specified.

 

Do all DCH340's have the same fittings on them such as fuel, water, vacuum, emissions, etc.

 

Do California variants have anything different?

Yes, CAL versions differ in some years and models.

[Cardinal Grammeter]

Well, I got one from a 1977 620 L20B coming from CA so it will be at least a week before I get it.

 

It will be a joy to get that plywood 1-bbl off :o)

 

Need to get a vacuum hose schematic or pics.  (I'll wade through the shop manual again.  There is a cutaway pic of everything that is very busy and nearly impossible to make out, but I think everything may be shown.  Will have to get the magnifying glass out.

[LenRobertson]

I don't think these Dime Quarterly articles will specifically answer your questions, but you still may find something of interest if you are messing with Hitachis. Especially if you need to rebuild one. Look at Volume 1, Issue 3 and Volume 2 Issue 1 here: http://dimequarterly.blogspot.com/p/back-issues-ordering.html

There is some information on different jet sizes that you may need depending on which Hitachi you can find.

 

Len

[LenRobertson]

There are a whole lot of dead links on this page: http://www.davidcmurphy.com/olddat/620tech.htm

but the link for the 1974 620 Factory Service Manual seems to be working. The download is 435 pages, so I didn't wait to see what was there, but usually the FSM has really detailed diagrams of vacuum lines and wiring and so forth.

 

Len

[Cardinal Grammeter]

LenRobertson,

 

THANK YOU SO MUCH for those dimequarterly references.  I skimmed both parts of the carb tuning article and was believe Part 2 may have the best discussion of emulsion tubes that I have run across.

 

Since I have been a Paton Supercharged Studebaker guy my entire life, I've always been trying to figure out ways to improve fueling of the blow through carburetor.  And its all Secondary Air Bleeds and Emulsion tubes.

 

SAB are pretty simple, but the ET is the Final Frontier of carb tuning in my opinion.

 

And a comment about the Hitachi:  Just seeing that it has replaceable SAB jets puts it in the league of Webers which shames the Holley and Carter carbs of the Muscle Car Era.

 

NOTE:  You should see the emulsion tubes in AFB carb Studebaker used on their supercharged engines.  After I read Part 2, I'll tell you what they did!  What is interesting is that with a centrifugal supercharger, change in boost is the square of change in rpm.  This means change in fuel flow must be the same square relationship with rpm.  The kicker of all this is that the simple venturi and Bernoulli's Principle is just such a square relationship (think stagnation pressure "rho v squared") but the normally aspirated carb has all kinds of embellishments to make it a linear flowing device instead of a square flowing.  The SAB is the first step in that domestication.  So I will be VERY interested to study Part 2 :o)

 

Thanks so much AGAIN,

Tom

[LenRobertson]

Good to hear you found the DQ articles useful. I need to reread them myself. I remember them being quite interesting. I don't know if different size jets for the Hitachi 340 are available from Nissan. Possibly the DQ articles indicate where to get jets.

 

I've been a Stude fan for many years. When I got out of high school and attempted college for the first time I drove my brother's 4-door 6-cylinder Stude (Commander?). I think it was about a '54, but it had been wrecked and the grill was gone, so I don't have much of memory of what it looked like. I should have saved that car from going to the wrecking yard when my brother decided to get rid of it.

 

There is a local shop here in town that specializes in Studebaker restorations. I'll have to ask him if he ever gets any supercharged cars. I suspect they are pretty uncommon models. I know he has had a couple of Avantis, but I can't recall if there was a blower option for those or not. I've even considered looking for an early '50s Stude as a project, but Datsuns keep me busy and are way cheaper to mess around with.

 

Len

[ggzilla]

Nissan sold jets five years ago but they may not have them any longer. I would get a parts carb, and drill the jets out slightly. Keep the original jets in case it runs better with them.