DCH-340 DCH340 Identification, Adjustment, Issues, etc.

[Cardinal Grammeter]

I've got two to choose from. 

 

Carb on left:

• has a spade terminal on the anti-dieseling solenoid
• wiring is routed to front of carb (602 has loom on firewall)
• better condition

Carb on the right:

• no spade terminal (all peg)
• torn accel pump boot
• busted fuel inlet nipple
• wiring not rounted to front
• poorer condition

I don't know if either carb works.

 

Here are the pics:

 

 

Edited January 24 by Cardinal Grammeter

[datzenmike]

 

Says L20B on the left carb so by elimination the right one is for the L18.

 

The right one also has the older style choke heater.

 

 

 

Spring missing on the L18 carb

 

 

The broken part is the banjo fitting. You'll see why when you remove it.

 

 

These carbs are basically the same. Larger jets in the larger displacement L20B carb and the other differences are mostly emission changes that happened every year. You can just swap parts to make a complete good one. If you go with the L20B carb don't forget to swap the L18 primary and secondary jets into it.

[Cardinal Grammeter]

Missed the "L20B" on the choke - I knew there was writing there but didn't pay enough attention to it.

 

Did the L20 use a two pegs and a spade connector?

 

Oh, the carb on right could be for an L16, right?  Also, it has an extra "tab" on the throttle linkage - perhaps for an automatic?

[datzenmike]

On the L20B carb...

The Red wire is for the idle cut solenoid.

The Blue wire is for the electric choke

The third wire is for the BCDD solenoid. It's the thing that looks like an idle cut solenoid but mounted to the BCDD, which is the round thing on the side of the carb with the small Black rubber plug

 

 

They do much the same thing but over the years bullet and spade connectors changed.

 

The 'tab' on the linkage is likely for a dash pot. Maybe for automatic. Could be for L16 or L18. Not an L20B carb it's too old. 

 

The front cover with the round 'bull's eye' glass is from a later L20B carb, or I should say I have never seen one on an L16/18

[Cardinal Grammeter]

I have a 3rd carb, but it is a basket case - all torn apart.  But it is perfectly clean.  It is not new because you can see some obvious wear on slotted screw heads where they weren't careful with the screwdriver.

 

QUESTION:  In these parts, there is a 1/2" thick phenolic spacer - I will use it but was it used on all 620's?

 

The electric choke cover is missing, but it does have the "non-glass" bowl cover. 

 

I'm tempted to swap throttle plates on the "right hand carb" since there is a lot of wear in the primary throttle plate shaft.

 

Too bad they didn't stamp the model number of these carbs.

 

I'm going to need some help with the vacuum hose connections since I have nothing to go by.  I've looked through the shop manual, and while they say "to carb" for instance, they really aren't specific.  I'm thinking this information would be a good new thread topic.  (And then there is the fuel tank evaporation system...)

[datzenmike]

I think that spacer is on all carbs. Certainly on L20Bs. It's to prevent heat transfer to the carb body. L20Bs run hot and the gas can boil right in the float chamber making hot day restarts difficult.

 

These were all DCH340 carbs only the internal jets and bleeds and things were different. Most parts will interchange on them including the earlier glass front cover with the later metal one with the round glass.

 

Every year the emissions equipment and numbers changed and 'stuff' was added and retired to meet the newer rates. Then there's the California emissions equipment and to some extent the automatic was slightly different from the manual. Some emissions equipment affected the intake side, some the exhaust side.

[banzai510(hainz)]

get a weber 32/26

sooner you do this the sooner you will be set FREE

[Cardinal Grammeter]

Yeah, I was thinking about that.  But I'm hooked on "unmolesting" this 620.  I'm now on a quest to... (gasp)... restore all the emissions controls.

 

I really wish I had an early L16 620.

[datzenmike]

The early L16s had a retard set of points, a flow guide valve, zero vacuum advance at idle, an air injection into the exhaust manifold, coolant warmed/cooled intake manifold, warmed air intake, hot idle commentator and a PCV valve. This was the extent of the emissions controls. L18 had this and an EGR valve

[Cardinal Grammeter]

Nothing searchable about DCH340 insulators.  After researching all the 620 variants, I'm going to start a new thread specifically for "DCH340 Insulators" for everything we know about them.

[Cardinal Grammeter]

UPDATE - HUGE NEWS:

 

Starting to prep carb for install and due to some unforeseen problems, I revisited my "vast" collection of DCH340's.

 

You've seen the two "complete" carbs.

 

What you didn't see what the "basket case" carb and incomplete set of parts that went with it.

 

This all started when I ordered a carb kit on eBay that did not have the accel pump bellows(!)  I thought this was shocking since that exposed rubber piece is the first thing to fail - even before the pump!  So BEWARE!

 

The kit was for a 73-74 1.6, 1.8, 2.0 which of course makes no sense, but the airhorn and throttle plate gaskets were different - on both of the carbs in this thread, of which one says L20B on the automatic choke cover.  This forced me to closely look if I could mod the gaskets to use them (which was sort of academic since I would have to get a kit with the bellows.)

 

Then I started hitting the parts bag for the basket case carb.

 

Soon I realized this parts carb was different from the 2 I've posted here!  In fact, the airhorn and throttle gasket fit!

 

But here is the kicker:  in the parts bag, I found a small aluminum tag (about 1 x 1/4")  that would have been under probably an airhorn screw (just like Carter and most other carb manufacturers did) that said  "L18MT" and a "12" underneath!

 

Holey Mackerel Bat Man.... the parts carb is the carb for my truck.

 

Now some identification details, the early carb can easily be differentiated from the L20B carbs:

• Early has exposed, one of the large threaded slot head brass plugs on the top of the carb body - the airhorn does not cover it  (L20 does cover it)
  • 
• Early has very long (over 1") standoff on secondary throttle shaft for the vacuum secondary  (L20 is maybe 1/2")  This is because:
  • 
• Early secondary vacuum unit "protrudes" much more.  (L20 is "tucked" behind the B.C.D.D. unit)  In fact, the vacuum unit is pretty much not in the "shadow" of the B.C.D.D.  (see 1st pic)
• Early has the airhorn needle valve adjustment jet in the body but in later carb, has it in the airhorn along with the needle itself.  This is a big improvement because changing the airhorn gasket will effect the adjustment in the early version if there is a difference in gasket thickness.
• There are a number of differences with regard to holes, jets, gaskets that are different.  (at this time, I don't have anything written down but don't remember which "way the differences go" with regard to the carb types.)  You can see some differences on the original pics in Reply #1:
  • BOTTOM VIEW:  Can clearly see the 1/2" Vacuum standoff on the secondary throttle shaft
  • FUEL BOWL VIEW:  Differences between the 2 later model carbs;  The RH carb has a "larger, blockier" feature on the RHS of the airhorn.  If you look closely, there are a number of differences in the airhorns.

So it looks like I'm going to resurrect the parts carb but what is really nice about it, the airhorn, body, and throttle base are like new!  I don't know how they got that carb so clean.

 

And I will have the "coveted" correct carb tag to boot!

 

(Yes, I know pics would be monumental, but having to host them really takes the wind out of my sails....  But seriously, I believe this is very useful and critical information, and if I host them on whatever, eventually they will come down and the information will be lost.  Wonder if Google hosts pics?  I don't think they do.  But Google could be counted on psychotically hoarding every scrap of information they can get their nerdy hands on.)

[LenRobertson]

I'm going to mention something that I personally would consider in choosing between two Hitachi 340s. Looking at your fifth picture (looking straight down at the top of the two carbs), I'm going to refer to what my '79 200SX FSM calls the "Small venturi" (each of the primary and secondary carb throats has one. You can only see the one on the secondary side due to the choke butterfly on the the primary side). This is the small round tube-like thing suspended down the carb bore - above the throttle butterfly and below the choke butterfly on the primary throat. Your two carbs seem to show the two different mounting types for the venturi. The RH carb has the venturi mounted on an arm from one side that is held into the carb body by two screws. This page: http://www.carburetorfactory.com/expvw29.htmlshows the latter style small venturi holder (#69 and #74).

 

The LH carb has the venturi mounted on a bar that goes from one side of the carb throat to the other. See here:

http://www.fuelpumpsusa.com/AUTOPARTS_PICTURES/beck%20arnley/162-9553/beck%20arnley_162-9553_2.jpgThe circled area on the right of the exploded view shows the venturi holder that fits clear across the carb throat. You can see on one end of the holder is a tiny O-ring and on the other end is a "Spacer". From outside the carb body is a setscrew that bears against the spacer and holds the spacer and venturi holder into the carb - in theory. I've now had two Hitachis with the spacer missing and the venturi holder loose in the carb throat. I assume when the spacer goes missing it goes through the engine, although I suppose it could have been lost in a previous rebuild. With a missing spacer and a loose venturi  holder, I don't imagine the O-ring seals very well, so the gas coming through that passage may not be going where it is supposed to.

 

Anyway, given the choice of carbs with the two different style venturi holders, I would choose the one held by two screws into the carb body (the one on the RH in your pic). Maybe there is something inferior about the carbs with this style ventri mount. If so I would love to know.

 

If you have the style with the spacer and set screw in from the side of the body it may be just fine, but be sure to check that the spacers are in place on both primary and secondary sides and the venturi holder is in there really tight. The set screws are staked into the carb body and I'm not sure how easy they might be to turn to tighten or to loosen if you want to remove the venturi  holder to replace the tiny O-rings. I also wonder if the carb body is soaked in carb cleaner if this hurts the O-rings and they should be replaced. So if anyone has any comments on all this Hitachi trivia, please post.

 

Len

[Cardinal Grammeter]

Thanks Len!

 

I got a L20 carb kit and was wondering what the o-rings were for!  And I'll bet the two venturi styles are associated with the two airhorn gaskets that come with the L20 carb kit.  Definitely would choose the Old School screw mounts.  However, I'm using my 3rd "basket case" carb since it definitely is NOT a L20 carb and most likely an actual L18.

 

TIP:  Jet Stamping numeral "1" looks like a "7"  (who could have seen that one coming!)

 

In further trying to confirm I have an bone fide L18 carb (have a L18MT tag in its parts bag), I scoured all the carb jet part numbers and discovered I have the proper #100/#170 used by the L18.  However, the power valve is a #43 instead of the #41 called for.

 

NOTE:  I have 2 power valves loose, a #43 and #47.  The #43 is the bigger hole!  Go figure.  It could be like Carter that some of the numbers stamped on jets have NO relationship to the orifice size - they are more of a part number.  I'm going to use the smaller one since I think I have (1) L18 and (2) L20 carbs - well, I KNOW for certain the 2 in the pics are both L20's - the short vacuum standoff and "hiding behind the BCDD" is a dead giveaway of the L20.

 

What is really unexpected is that with all the number/replaceable emulsion tubes, bleeds, and jets, the power valve vacuum threshold is set by the spring on the long plunger protruding down from the airhorn that is not replaceable.  (I suspect that the spring in the power valve has no contribution because although different in my two samples, they are puny compared to the plunger spring.  But that plunger spring cannot be changed.  You can't get the foot off and to remove the plunger/piston assembly, you have to remove a staked in disc from the air horn - definitely NOT something you casually do. 

 

EUREKA - ANSWER:  The #47 is actually a #41.  The "barb" on the top of the "1" character is highly exaggerated on the Power Valve.  They do the same thing on the jets, but the "barb" which highly misleading is less pronounced than the PV.

 

I also extracted Power Valve and Jet #'s for all 4 variants of the carb in the online parts manual:

 

                L16 early   |------L16 late--------|     L18      |---------L20------------| 

                                                            NOTE:  (65) denotes # in picture

Power Valve:      #50(65);                   #53(64);   #41(62);             #40, #43-CAL(64)
 

Main Jet (pri):  #112(57);  #97.5-7211, #98-7212(57);  #100(55);  #99, #101-CAL, #108-CAN(56)

Main Jet (sec):  #155(58);                  #170(58);  #170(56);                     #160(57)
 

Slow Jet (pri):   #48(59);                   #48(59);   #45(57):                      #48(58)

Slow Jet (sec):  #180(60);                   #90(60);   #90(58);                     #100(59)

[Cardinal Grammeter]

Regarding carb specs and tuning, the Datsun 1200 crowd is where its at!

 

Tuning

 

And from there they have carb specs.  On one page, they have every single consecutive jet # and its factory part number.

 

These guys are serious (!)

[LenRobertson]

Thanks for posting the link to the 1200 site. I always think of them as just being for smaller Datsun engines like the A14 and A15, but they have a lot of good information that applies to the L series.

 

You probably have seen the Dime Quarterly two part carb series, but I'll post the link anyway for anyone who may not know about it. http://dimequarterly.blogspot.com/p/back-issues-ordering.htmlVolume 1, Issue 3 and Volume 2, Issue 1 have the downdraft articles.

 

This page from the 1200 site: http://datsun1200.com/modules/mediawiki/index.php?title=Hitachi_DCH340under "Airflow" shows two different specs for venturis for DCH 340s for L18 or L20. Probably not enough difference in size to tell much in performance, but may be another way to ID different carbs.

 

Len

[Cardinal Grammeter]

Trying to assemble a correct carb from a "pile of bones," I feel like a paleontologist.,,

 

Found the fast idle adjusting screw linkage was severely mangled.  The correct one then allows the fast idle cam overtravel stop to work properly.  It is amazing how people have butchered various systems for whatever purposes.

 

Right now I'm dealing with the banjo fuel fitting.

 

My two L20 carbs have a larger diameter banjo as the basket case one.

 

I have carb kits for both early and late carbs and they use the same needle/seat assembly, but the two banjo types have different IDs.

 

The large bore banjo clears the fuel filter but is sloppy because the bore is so big - it doesn't come close to centering under the bolt. 

 

The small bore fits neatly on the needle/seat assembly.  However, the fuel filter now sits too high because it sits on top of the bottom id flange of the banjo.  So if the small bore banjo is correct, then there is a "shortie" fuel filter I do not have.

 

But that still does not answer the question why the big bore banjo is so sloppy when installed.

 

NOTE:  both the big and small bore banjo have the same diameter fuel nipple so why are there two bore sizes?

 

Edited January 24 by Cardinal Grammeter

[Cardinal Grammeter]

UPDATE:

 

EUREKA - ANSWER:  Power Valve selection:

 

The #47 is actually a #41 and the correct one. 

 

The "barb" on the top of the "1" character is highly exaggerated on the Power Valve.  They do the same thing on the jets, but the "barb" which highly misleading is less pronounced than the PV.

[LenRobertson]

All this carb discussion reinforces my belief that no professional mechanic in his right mind would ever try to overhaul a customer's Hitachi. No way of knowing if the carb on the vehicle is a replacement from a different year or how many bent or missing pieces or stripped threads there are. Even ordering the correct carb kit can be challenging if you can't ID the carb exactly. However, we amateur mechanics who have all the time in the world are free to dick around with old worn out carbs as much as we can stand (before going crazy).

 

On the subject of carb ID, I had a 340 outside this morning looking at something and I saw the elusive numbers etched into the carb body! I knew I had seen them before on other carbs but could find them on this one - until the light was just right. These are not stamped into the body, they are done in some sort of "ghost writing" that may be visible on a new carb but ten to disappear with age. I looked on another 340 and couldn't find any numbers. I suspect over use of carb cleaner eats them away. Anyway, look around the corner from the RH end of the float bowl cover. They are etched on the flat surface of the outside end of the float chamber, and very well be difficult to see unless the surface is clean and the lighting is just right. On this particular carb, I can make out DCH 340 43A 6501H; at least I think that is what I'm seeing. Somewhere recently I saw a chart of different Hitachi models with these more complete numbers, but can't find it this morning.

 

The power valve from this carb is a #43. Primary main jet is a #99, and I can't read the number on the secondary jet.

 

Len

 

 

[Cardinal Grammeter]

Rebuilding a carb can be daunting.  But if it is an AFB, a blind incompetent monkey could do it.

 

As far as the DCH-340 goes,   I now know a lot about them.  And could do what's taken hours to learn,  now in minutes.  But only because I've actually held the different parts in my hand.  Try and figure out what the right spring is!  There is NO information in the parts manual to help identification.  Even the accel pump ball, weight, and spring at the nozzle end is all over the place.  One of the carbs had a spring installed over an emulsion tube that fits way down in the hole!

 

EDIT:  Coming from the AFB world where "emulsion tube" is never uttered, I am absolutely amazed that every single jet, bleed, and tube is replaceable and #'d.  I mean we're talking about multiple emulsions tubes - not just one per bbl.  And I thought Webers were sophisticated.

 

I really do feel like a paleontologist!  :confused:

 

Your carb is interesting.  According to the parts manual the #99 Main is a non-CA, but you #43 Power Valve is a CA.

 

The CA emissions carbs have larger jet #'s and assuming that a larger # is a larger orifice, they were trying to eliminate NOx which is what SMOG was all about (if I remember correctly.)  So they richened the carbs up.  Of course what they did with timing, who can say.  The end result was CA emissioned cars ran crappier.

 

I sort of solved my fuel fitting problem but now I am either missing or have misplaced (I could have sworn I had both types in my hand) the fuel nipple support bracket.  The <L20 carbs used a "shorter" bracket since the bracket screw is closer to the needle/seat fitting. 

 

I remember distinctly trying to install one that didn't fit properly and then I had two of them loose - one was crimped over the fuel nipple and had to be spread (the other one didn't.)  So now I'm cleaning up all my work areas trying to find the, hopefully misplaced one.  I swear I had both brackets in my hands and compared them.

 

I could cut up a "long" one but could not bear to ruin a part for these carbs - I've just seen too much of that.

 

I could make one, albeit would be a simpler design.

 

I'm kind of caught up in "restoring" my L18 carb and would actually like to go through and check all the parts in the two L20 donors I have, get all the missing/ruined pieces, and rebuild them.  While a fun project of scrounging and scrutinizing, I so don't have the time!

 

I've encounter The Carburetor Factory a lot in my searches and am going to call them and see just what parts they have.

 

It appears that there was a Nissan rebuild kit (its in the parts manual) that was quite extensive.  Or so it seems.  The picture identifies a lot of parts, many with "A", "B", etc. but there is no parts list.  So it's not clear what is in the kit.  Of course it is a OEM kit and probably very NLA.

 

Eventually I will post all the pics I've taken (many) on Photobucket, and make some entries on my build thread.

[LenRobertson]

Looking at my notes for the last 340 I tore apart, I see two air bleeds (#100 on the secondary side and a #48 on the primary side) have a small coil spring on top of them, then a plug on top of the spring. I was curious about the purpose of the springs, but I may never know. Lots of mysteries in life I guess.

 

Another thing I'll mention for the benefit of anyone following this thread and trying to tame a Hitachi - it is worthwhile to use blue Loctite on the screws holding the cast iron carb base to the main body. I'd read that recommendation, but didn't do it on the carb on my 510. Sure enough, the car started running poorly and it took awhile to figure out those screws had loosened up. I also didn't bolt the air cleaner to the brace from the intake manifold. Leaving those two bolts out lets the weight of the air cleaner leverage the upper part of the carb and loosen the screws that hold the carb base to the body. So next time I'll know to do it right. Loctite and air cleaner brace for me.

 

The 340 I'm running on my 510 now doesn't have that bracket to support the fuel inlet nipple. I've run it that way for quite awhile, but it probably isn't a good idea. I need to dig through my parts and see if I can find one that fits. It would be a bad place for a gas leak if the banjo bolt did loosen.

 

I've located four spare Hitachis in my collection, but I think I may have more I can't find. It sounds kind of ridiculous to have that many extra carbs, until you have missing pieces on a carb you are trying to rebuild. Then you can't have too many to scrounge from.

 

Len

[Cardinal Grammeter]

STATUS UPDATE:

 

I went with the big bore banjo fuel fitting with the plastic strainer. 

 

The plastic has a larger OD than the thin aluminum top and bottom banded strainer.  The plastic is very snug on the needle/seat fitting and obviously seals there.  The aluminum is loose diametrically but protrudes in height so that when the banjo is tightened down, it crushes this strainer thus forming the seal.

 

So that leaves the fuel fitting nipple support bracket (officially called the:

 

13

PLATE-STOPPING

 

16137-N0910

 

 

As I said, I recall having two in my hand that were different.  I thought it was Long -v- Short. 

 

Turns out I have two variants of the Long #13.

• The difference is related to the shape of the airhorn:  large -v- small cutout where the #13 engages.
• The screw is located in the same place in both.
• The major difference between these two L20 parts is that one carb has the old style screw in booster venturies while the other has he weird o-ring style.

So I'm pretty sure I'm missing that part.

 

I do have the proper Short

11 LEVER-LOCK   16138-A0110 L16   -   1

which locks the banjo restraining bolt.

 

EDIT:  I was out looking at making something quick and dirty and realized there is another variation in this L18 carb:  The horizontal surface this support braket lays on is at the C/L of the fuel nipple.  This means the bracket has to have a jog bent into it.  The other brakets (L20's) can be fabbed from a piece of angle.  This bracket is not so simple, it has an angle and a jog bent into it.  In fact, I found what I think is the correct part.  Note that it does not have notch that engages the airhorn feature.  (NOTE:  I definitely did not have this bracket!  So at least I'm not losing my mind... at least totally) [i've burned so much time on this project, I might as well make a decent replica.]

 

IGNORE THE YELLOW ARROW:

 

 

So is it worth installing the support?  worth scrounging the correct one?  worth making something that simply works?

 

For now, get the carb on the engine and get this thing fired up!   ....oh.... have to do something about the missing EGR tube....

[Cardinal Grammeter]

I made one out of a weird, dead soft stainless.  It was about 1/2 the thickness of the above pic, but considering people run these carbs w/o the bracket, it should be good enough.  Definitely works when tightening and loosening the banjo.  W/o the support, and loosening, the needle/seat comes loose - you have to react the nut torque at the banjo.

 

 

So the carb is DONE.

 

I still have to do something with the EGR tube before I can fire it up.

Edited January 24 by Cardinal Grammeter

[Cardinal Grammeter]

Yeah, I saw that spring on top of one of my air bleeds too.  It is short, maybe 1/4" tall and just 2-3 turns - quite a stiff little spring.

 

My theory was that it was mistakenly put there since there is a spring over the accel pump nozzle "weight" which is over the ball.

 

In the parts diagram, there is no such spring.

 

NO CLUE on this one BUT I did have the notion that the jet tube that was down in the hole (it was an emulsion tube/jet) was possibly not tight, so could it have come loose and the spring was a stop gap method to keep it at least lightly seated?

 

Regarding the accel pump nozzle stuff, there are two versions:  big weight above ball and small weight with very long weak/fragile spring with many turns and a threaded plug that has a locating pin for the spring.  But that is about it for a spring "down in a hole" under a plug.

 

Again, too bad can't post pics directly... you'd think that Google would gladly offer forums a decent pic storage space considering that PhotoBucket is unlimited.

[Cardinal Grammeter]

Just noticed (Duh!) that there are Kits A, B, and C. 

• A is gaskets
• B is screws (appears to be ALL the screws)
• C is e-clips, washers, and other stuff

Wonder if they are still available?  (too bad all the Nissan dealer web sites use the service which does not show discontinued parts - you see a price and it means nothing.)

[Cardinal Grammeter]

...

 

Another thing I'll mention for the benefit of anyone following this thread and trying to tame a Hitachi - it is worthwhile to use blue Loctite on the screws holding the cast iron carb base to the main body. I'd read that recommendation, but didn't do it on the carb on my 510. Sure enough, the car started running poorly and it took awhile to figure out those screws had loosened up. I also didn't bolt the air cleaner to the brace from the intake manifold. Leaving those two bolts out lets the weight of the air cleaner leverage the upper part of the carb and loosen the screws that hold the carb base to the body. So next time I'll know to do it right. Loctite and air cleaner brace for me.

 

The 340 I'm running on my 510 now doesn't have that bracket to support the fuel inlet nipple. I've run it that way for quite awhile, but it probably isn't a good idea. I need to dig through my parts and see if I can find one that fits. It would be a bad place for a gas leak if the banjo bolt did loosen.

 

I've located four spare Hitachis in my collection, but I think I may have more I can't find. It sounds kind of ridiculous to have that many extra carbs, until you have missing pieces on a carb you are trying to rebuild. Then you can't have too many to scrounge from.

 

Len

 

I was wondering if you had a "normal" base gasket or the really thick one used in the L20?  I could easily see that thick one working loose.  Its approx 1/8" thick and made out of some hard composite material - not totally solid but pretty hard.