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Topic: Carb
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superc_1
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 bullet Topic: Carb
    Posted: 30 January 2007 at 4:47pm
Now that I've got my engine fixed I need to ask about the carb. I put a new hitachci on it (remanufactured) and I was wondering is there a good or a bad way to lean the carb out? I want to get the best gas milage out the carb. The truck is just my daily driver, and I say that with a warm heart. Any suggestion would be great. P.S. I have been turning the idle screw down half a turn everyday I'm hoping this will get me better milage without harming performance (what little power they have in the first place). The carb box said it was tuned for best result at the factory with a wet flow test , but since all the smog stuff is gone I think the carb will need adjusting.
77 yellow king cab
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datsunaholic
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 bullet Posted: 30 January 2007 at 5:15pm
The idle screw doesn't do anything off idle- the entire idle circuit is essentially disabled when the throttle opens. The ONLY way to lean out the Hitachi is to change the main jets. FINDING new jets may be problematic.

You don't want to go too lean. You'll burn holes in the piston crowns.

I got 35MPG out of my '76 KC, but only with the following:

NEW Weber that's jetted for a 1.4L B210
L18 engine
280ZX ('82) tall-overdrive 5-speed
A "Light" foot
Narrow, tall rear tires (205/75R14s)

The Weber improved things a little, as the original carb was pretty much shot. The 5-speed made a massive difference from the original 4-speed- around a 50% gain in freeway mileage (I'd been getting around 25MPG). City type driving didn't change at all.
'64 320
'68 520
'72 521 V6
'74,75,79 620s
'76,78 4X4
'76 KC
'72 510 Wgn
'78 B210
'78,81 510 Wgn
2X '78 510 Coupes
'83 720 KC

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lynchfourtwenty
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 bullet Posted: 30 January 2007 at 5:18pm
does anyone have a working carb they want to get rid of, my buddys 76' could sure use it.. the things been sitting for like 2 years now cause of a bad carb, lame excuse if ya ask me, but i told him i'd try to find one for him so he can drive it
77' 620, weber, header, A87 head 2" exhaust. Tahoe Wheels with Kuhmo tires, More upgrades this summer
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superc_1
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 bullet Posted: 30 January 2007 at 5:33pm
I don't think I'll change the jets. I saw a guy use a mananer? Basically a water column to set a carb? Is this a good way? Also, are most datsun pretty cold natured? Mine runs pretty rough til it warms up or could I have the idle screw down to far?
77 yellow king cab
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lynchfourtwenty
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 bullet Posted: 30 January 2007 at 5:53pm
sounds like a datsun to me
77' 620, weber, header, A87 head 2" exhaust. Tahoe Wheels with Kuhmo tires, More upgrades this summer
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lynchfourtwenty
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 bullet Posted: 30 January 2007 at 5:55pm
But make sure u dont take the idle screw down too far, change your fuel filter, run some Chevron 92oct, also check the choke.. not sure if u can adjust the stock carb ones or not but just incase..
77' 620, weber, header, A87 head 2" exhaust. Tahoe Wheels with Kuhmo tires, More upgrades this summer
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datsunaholic
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 bullet Posted: 30 January 2007 at 5:58pm
There are 2 idle speed screws- the "Main" idle speed screw and the "Cold" idle screw. Then there are the choke adjustment and the mixture screw.

The Main idle speed screw and the mixture screw ONLY have effect when the engine is at true idle and at full operating temperature. So these should only be adjested then.

The fast idle (cold idle) screw is factory set, and contacts the fast idle cam on the carb linkage - it COULD be set too low, causing rough idle.

Or, the choke is opening too soon, which in cold weather causes overly low idle as well as a too-lean condition when cold (should be rich at start-up).

They are cold blooded, though. Most of mine when cold start up around 1500RPM and drop to idle within 3 minutes. Some drop too soon and the engine isn't warm enough yet.

I've never used any fancy equipment to set a carb. Just ears, eyes, and nose.
'64 320
'68 520
'72 521 V6
'74,75,79 620s
'76,78 4X4
'76 KC
'72 510 Wgn
'78 B210
'78,81 510 Wgn
2X '78 510 Coupes
'83 720 KC

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nismopu
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Joined: 10 December 2006
Posts: 47
 bullet Posted: 30 January 2007 at 6:15pm
Ok well I wish you were around here to help me with mine, I just put a carb rebuild kit in it and now its worse! The problems before was that one of the main body screws kept backing out and I had tried everything to keep it in there except a set screw. I knew I should take it off and check things out anyway, so I bought a carb rebuild kit in hopes of getting better performance out of it. Well the only good thing that came out of it is that the secondary's kick in all the time and it seems to be getting better mileage. The bad thing is trying to keep it running at stops(hot or cold) and bogging off the line. I believe I set the float height incorrectly as this seems why it bogs right off the start and I have to burn the clutch like mad to keep from stalling out. I also think I got my choke (lean/rich) thing bacvk where its supposed to be since I didnt take it off the shaft in the first place. Anyway, anything else I should look at maybe?
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lynchfourtwenty
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 bullet Posted: 30 January 2007 at 6:25pm
i think holic pretty much covered it man Smile
77' 620, weber, header, A87 head 2" exhaust. Tahoe Wheels with Kuhmo tires, More upgrades this summer
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datsunaholic
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 bullet Posted: 30 January 2007 at 6:41pm
Bogging out is usually a case of the accelerator pump being wore out, installed backwards (never rebuilt a Weber bit I hear it's possible) or on a Hitachi using the wrong lever hole on the pump plunder rod.

Can also happen with the dist vacuum hooked up to the wrong carb port.

With Hitachis it's far too common to warp the carb body taking it apart- the upper body is pretty weak aluminum and I've warped enough to know it happens.

I've also had crud plug up the primary main jet- engine will idle, and run off the accelerator pump, but nothing else.
'64 320
'68 520
'72 521 V6
'74,75,79 620s
'76,78 4X4
'76 KC
'72 510 Wgn
'78 B210
'78,81 510 Wgn
2X '78 510 Coupes
'83 720 KC

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nismopu
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Joined: 10 December 2006
Posts: 47
 bullet Posted: 01 February 2007 at 1:16am
DOH! I just reviewed the pics I took of the carb and notcied that it was in the upper hole on the accelartor pump, lol. I believe its in the lower one but I will check tomorrow when I get home and see whats up. thanks for the tips man. peace.
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