Hitachi SU tech pages
Try this site too. It's listed in the "Web Links" under Tech info.
I think you have made your decision, but I'll throw in my 2 cents anyways. I'd lean toward the SU's mainly because I don't like the 32/36 + adaptor plate+ stock manifold combo. I used to have this in my car. It worked ok.
Now I have twin 38mm Hitachi SU's. I seem to get a little more power from these. I'm also still trying to understand how, when and why they work. But they do work and I know they're not in tune. I haven't check to see if they are in sync for over a year and the damper on one doesn't feel as stiff as the other. Did i mention the homemade linkage with no way to adjust each carb without disconnecting them? How about the 34mpg?
So don't worry about these things not being perfectly in tune. You can mess up the adustments on a 32/36 just a bad as you can an SU(type) carb.
I think 2 38mm openings feeding air/fuel is better than a 32mm and a 36mm opening that gets necked down by the adaptor plate on a tiny stock intake.

Quote:By "stock" i mean a factory standard, unmolested engine. It matters not if it is an A12 or A14, so long as it has not been modified in any substantial way, then it qualifies as "stock"

The original carb was configured by the factory to give it's best all round performance. Changing the jetting just makes things worse in the majority of instances.
I'l go with Feral on the timing. The ignition will give it's best if you have a "dwell angle" meter with inbuilt tachometer, & a quality timing light. Set the dwell on the lower end of the specified range & recheck the timing after about 5,000k to make sure things are still where they should be.

AlphDoti
The hoses are most likely in the correct position.

The loss of power is most probably due to retarded spark.

Advance the spark to 12 degrees when cranking. If the engine makes a knocking sound under load in the high gears take it back 2 degrees then check it again.

Repeat this, retarding 2 degrees each time till the knocking noise cannot be heard at all at under load in high gears. This will give maximum power and also best economy.

DodgeMan said "If your engine is stock, then do not change the jet sizes away from stock sizes as these are a proven combination."

Which is stock engine? Mine is A12.

There are two vacuum tubes:
1). One runs from the air-cleaner housing to the inlet manifold.

2). Another runs from the ditributor vacuum advance unit to the side of the carburator.

Is this correct?

Yesterday I noticed that the car is so weak on high gears. Recently when I cleaned the carb, I just set the timing to produce spark on 0% when the crack is turned by hand. I do not know if the spark is produced at around 7 degrees on 600 rpm?
Could the lose of power due to retarded spark timing.

Your ideas great.

1). I am not sure if what I see is intantaneous squirt. Just wondering which direction the jet should be facing. Mine has the slanted side facing upwards (it's like a flute tube slashed diagonaly - you know what I mean). The fuel therefore, touches on the Venturi before dripping down.

2). The manifold Vacuum leak is possible because the openning is just around the loose (too free) shaft.

But why does it pick-up when I step on the accelerator SLOWLY?

Hi AlphDoti

Dodgeman pretty much covered it,I just want to add 2 things:

1- Make sure that you get instananious pump squirt opening the throttle SLOWLY,you should be able to see fuel almost dribbling out the pump Jet.

2-Make sure you havnt got manifold vacum at your vacuum advance on the distributor,
( It causes a similar symptom to what your describing)

AlphDoti
If your engine is stock, then do not change the jet sizes away from stock sizes as these are a proven combination.
The primary throttle shaft is the one that will wear the most as it is in use ALL the time, while the secondary is used only occasionally.
Contrary to what some may say, the original Hitachi carb is a good, proven design carb, & it is ideal when used in stock applications.

If you have a vacuum leak, it would mess with the idle more than anything else. If this leak was at the "manifold to head" gasket, the leak would affect one cylinder more than the others & may even show up as a missfire at idle. Vacuum leaks often whistle if they are in the carb area. Check the tightness of all manifold & carb bolts.

A worn throttle shaft may well have the effect that you describe. So will a faulty accelerator pump, which you have checked. If the primary shaft is badly worn, you have four options.
Live with it
Fit a good used base or carb.
Have the base reconditioned with new bushings & shaft.
Fit a new base assembly.
The last three are my recomendations.

A blocked intermediate circuit will also give you "off idle" problems. This can be checked by simply screwing the idle speed screw progressively open.[not the idle mixture screw] What happens is that as the throttle slowly opens, & the rpm's rise, the idle circuit can no longer supply enough fuel, & the airflow is not yet enough to start to draw fuel from the main metering circuit.

There is a small orifice, just up from the idle port, just above the throttle plate when it is closed, & it starts to feed fuel once the throttle is open a little bit. This fills in the gap between idle speed fuel needs, & the time when the airflow is enough to draw fuel from the main metering circuit. If this intermediate circuit is blocked, the engine will lean out as you screw the idle speed adjustment in. & the engine will stumble. It may even stall. The accelerator pump will have no role to play when the throttle is opened as slowly as this, so it will not mask the symptoms.

Make sure that the engine is properly tuned, & all the idle settings are right on the money BEFORE doing this simple test. Also make absolutely sure that the fuel LEVEL is correct in the float bowl by inspecting the little window in the carb while the engine is idling. It should be in the middle of the window, level with the little dot marked in the glass. If it is not correct, then fix it before proceding further.

If this intermediate circuit is the problem, then pull the carb down & blow compressed air in the reverse direction through the port to clear it.

I hope this is of some help.
Chris

Lately my 1200 Datsun pickup 1993 has been hestitating and slightly jerking when I accelerate.
It happens both when the car is cold and warm and in the beginning of the acceleration.
Even when I change gear and start to accelerate!
There is a serious lack of power and it is so annoying... sometimes the engine stalls.

I recently changed my plugs, oil, and air/fule filters, battery etc...
Imagine, joining a High-Way and want to accelerate before the approaching cars arrive, there it goes duf duf, hesitate!

I have read many articles on this problem and they say the culprits are:

1). A light stumble only when accelerating from idle could possibly be caused by the idle adjusting screw,
being turned in too far. or

2). The accelerator pump circuit. http://www.theautoist.com/weber_carb.htm or

3). Acceleration hesitation is caused by Vacuum leaks.

Point (1) cannot be my problem, because I have adjusted idling and it's good.

Point (2) might not be the problem. But it is a potential. When I opened up the carb last week-end I made sure the Accelerator Jet squirts a fine spray into the throttle.

I have cleaned my carb many times making sure there is no blockage. One time I put bigger jets (two times bigger that what are there).
The problem disappeared but fuel consumption doubled, and the exhaust pipe turned black. The link above discourages
people from putting bigger jets to cure hesitation.

Could it be Vacuum leak? I suspect this because I realised that the Primary Throttle Shaft has too much free play.
On the contrary, the Secondary Shaft is tighter. Can this be re-built?

What do you guys suggest? I am feeling so bad about this problem.
I do not want to buy another carb if this can be solved.

It is a Hitachi carburator.

By jingoes

I didnt realise there ws soo much to it..
Well the throttle inkkage looks ok to me, but im not an expert on them. I am thinking that I will get them done by the pros and tuned by them as well.
I will be doing a pics session this break (next week) and i will get them up so that you guys can ave a captn cook...

On the top of each carb is a large, wavy edged, serated, or knurled knob. If you unscrew this by hand, you will be able to pull it out. It has a rod on the underside with a brass collar. This thing is a crude form of shock absorber & stops the internal piston, which is suspended on air pressure on one side, & partial vacuum on the other side, from bouncing up & down when driving. It also regulates the speed at which the piston rises when you hit the "power pedal".

Some blokes reckon it's the hot setup to leave it out, or at least run no oil at all. This is a total falsehood. Oils of difering viscosity are used to fine tune the opening rate & auto trans oil is often the recomended oil, but i used engine oil. This is a heavier viscosity & slowed the opening rate. The trade off is that my maximum possible acceleration was less than optimal, but i got great cruising characteristics & fabulous mileage.

L18_B110
The cam in my engine is described as a "Light Sports Grind" but no actual specs were forthcoming when i bought it from Repco in about 1983. I pushed the idle up to about 900 or 950 rpm & low speed characteristics were "quite acceptable" Like everything else, it's all a matter of balance, & i built my engine for my particular type of driving. It worked a treat for me & my particular application..