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Hitachi Carb Idle Issue, Gets Better in 3rd Gear??


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So here's what I got going on. 1972 521 4-speed 1600 with the stock Hitachi carb. All stock and all wires hooked up. Checked the linkages, choke and diaphragms and they're all good. The butterflies on both sides are where they should be with no extra large gaps. The truck starts up good in the morning and once she's warm the idle runs high. Funny things is that when I put it in 3rd gear, the engine runs down to a normal idle. With the truck in neutral, I unplugged the choke wire and there was no change, but with it idling in 3rd gear and the wire unplugged, it runs high.


There has got to be a wire backwards or something, but what I can't figure out is why only in 3rd gear does it drop down?? Any help would be much appreciated. Thanks.

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You have a Dual Points distributor. The 2nd (retarded) set of points activate when you are in 3rd gear, via the 3rd gear switch on the transmission(It was an early attempt by Nissan to lower emissions while cruising in residential areas). Under normal cruising conditions, the Dual points system will cause your ignition timing to retard in 3rd gear, as long as you aren't at Wide Open Throttle(WOT).


To eliminate this feature, I simply unplugged mine and set the timing on the advanced set of points.


Since it runs better in 3rd gear, it makes me think that perhaps your base timing may be too advanced and perhaps needs to be backed off.

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To eliminate this feature, I simply unplugged mine and set the timing on the advanced set of points.




There will be a small relay near the coil that depending on gear and throttle position, engages a retard set of points. Unplug this relay to disable it and it will run better on the advance set. Be sure to check and set your timing  now in,case it was wrong before.

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Micro, thanks for the info. Are you saying to turn the whole distro to adjust timing or the points themselves?


I'd say make sure your points gap is correct; always a good idea while you're in there. This is done with a feeler gauge and screwdriver inside of the distributor.


To set the base timing, yes, you'll have to loosen and turn the whole distributor. Do you have access to a timing light?

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That is the only thing I don't have but am going to buy one and get this done. I have set points on motorcycles in the past so this is not too hard a job. Just wanted to make sure I was on the same page about the distro turning. I do have feeler gauges and all the goods.

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Ok guys. I got her all timed up and the problem is fixed. Can't believe I didn't think about timing in the equation? Anyways, thanks to all for the help. I shall search for a Dizzy in the future!!

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I myself woulf just unplug the 2nd set of points.

then retime using the main set.


set your self FREE and find a electronic dizzy


You could also join the two sets of points and time it. First set would close last set would open. This gives you additional dwell time.

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