the dreaded hitachi, tuning

[willz]

was wondering if anyone could help me out.

 

rebuilt the stock hitachi downdraft for my L20b on my 78 620,

 

being young, dumb and full of... well..... dumb... I made the mistake of not paying attention to where my idle mixture needle was set and Its running a bit lean. which direction does this screw richen the mixture? the truck runs faily decently... but ive got some power loss/missing in the midrange rpm's and would liek to continue to fine tune the timing and fuel mixture, any help would be greatly appreciated

[willz]

also the auto choke I believe has had the spring tension changed... as in the spring doesnt seem to sit quite where it should and I was wondering if anyone had any pictures of how it should look on the inside as well as out. I have lined the notch on the cover up with the one on the carb and I still feel its not sitting in the right position. any measurements for the choke/butterfly would be awesome.

[ggzilla]

Hitachi is a good carburetor, don't be dreading on it.

 

When "rebuilding", set the idle mixture screw 2 turns out -- this is a rough setting at which the engine will run.

After installing, fully warm the engine, and turn the screw in and out until you get the best lean idle, where the engine runs the smoothest. Then turn it in (clockwise) until the engine starts to slow down just a touch. The engine must be fully warm to set this.

 

The automatic choke likewise must be set after installation. With engine cold, rotate the choke housing so that the butterfly closes 100% when the throttle is slightly opened. Back it off to where it just starts to open. Then rotate is just closed. Tighten it down. Warm up the engine 100% and verify that the butterfly is 100% open. Doesn't matter where the "marks" are, this is the correct way to do it. There are no measurements for this.

[datzenmike]

If you had the round black part of the choke heater off look inside it and be sure that the coiled spring connects to the little choke lever inside. If not, the choke butterfly won't close when cold.

[Rays74]

There are a few of us on here that know these carbs pretty well. Do the adjustments given above and let us know how you get on :)

[ggzilla]

Hitachi chokes can be silver or black. They both work the same, are same diameter, and are wired the same. One or two wire units are connected the same. Note the Hitachi symbols.

 

 

 

Center mark - WRONG (choke is not closed with carb/engine cold). Center mark is just an intial setting.

 

Correct for this carburetor for winter. Note that choke has fully closed with housing rotated this far.

It will vary by carb and choke heater -- and whether summer or winter

 

While checking the rotation, push the butterfly down and let it spring back. You want it where it will just fully close each time. If you turn it farther it may not open fully when warm.

 

ALSO IMPORTANT: Open the throttle a bit and check that the choke butterfly still closes all the way.

 

Tighten the choke housing screws (lightly, they are just tiny screws!), the warm the engine fully up, then ensure that the choke has opened 100%. Blip the throttle. If the choke is not 100% open (straight up and down) then the heater is not working correctly (may not be getting voltage, or may be worn out).

[ggzilla]

With engine FULLY warm, the choke must be fully open (butterfly plate must be straight up and down).

This is my other Datsun, where the center mark happens to be correct for summer.

 

 

When the engine is cold, if you rotate the choke housing clockwise and anti-clockwise, and IT DOESN'T MOVE THE BUTTERFLY, check to make sure it is installed right.

 

The Heater tang (in round part) must be installed clockwise of the Choke Butterfly lever (on carb)

 

You might be able to just look at the mark of the housing -- put the mark a bit clockwise in relation to the Lever

 

Double-check where the tang lines up in relation to the Mark when cold (some brands may be different).

 

 

After fitting the choke housing screws (slightly loose) rotate the housing anti-clockwise so that it closes the butterfly.

[datzenmike]

Good stuff.

[Silvester]

Some great information here. Ill be looking this up after i replace my bottom end.