Greetings to all members here. I am new and I joined to ask you guys about a problem I have. I drive a B310/120Y handed over from my dad.

I was tinkering with the air-mix and idle screws to reduce my fuel consumption (it increased after adjusting it previously). This afternoon, I encountered the following problems:

1) Once warmed up, it idles normal. When driving and coming to a stop, the engine dies. I do feel it hesitates slightly sometimes, but maybe it's just the rough road where I test drove it. Fixed!

2) When pressing very slightly on the accelerator pedal, the engine stumbles. Pressing more on the pedal makes it OK again, and sometimes when letting off the pedal it dies. Loosening the idle-mix screw solved it

NEW! 3) I have a bit of black smoke from the exhaust. The choke plate is opened and my idle-mix screw (if it is related to the problem) is about 2 1/4 turns out from fully seated.

4) Previously the engine would idle with a stable *dud-dud-dud-dud-dud-dud-dud* sound. After all this 'screwing' around it has become a slow and sloppy *plop-plop, plop-plop-plop-plop-plop, plop-plop-plop*. Turning in the idle-stop screw doesnt help much. Yes the idle rpm goes up but the plop-plop-plop remains

I found that the third circled screw would kill the engine if turned all the way in, and has a sweet spot about 1/4 turn out.

I'm sure you guys with decades of experience can shed some light on this matter. Thanks!

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Put it back the way it was as they cars aren't that bad fuel consumption wise

the one circled in red is the pilot jet if im not wrong and your not supposed to adjust it should be screwed in.

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I did adjust it previously (rough idle SOMETIMES, with aircond and lights on) but then my consumption worsened. After calling my dad, and as you said, I turned back out the air-fuel mixture screw (now at about 3 1/4 turns) to make a bit richer. The stalling is now gone.


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As I said, when screwed fully in the engine dies off instantly. Just a quarter of a turn out and it runs fine.

Judging from your pictures, your carb. is filthy. IF loosening the pilot is the only way that it will run, then the carb is dirty on the inside and needs to be cleaned. Be very careful when disassembling and write down what comes out of which hole, so that you can get the jets back into the exact same hole they came out of. It's not hard to do, it just takes patience. The only adjustable screws are the ones in the first pic, the idle stop, and the the idle mixture screws

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Thanks for your input. So the pilot screw is supposed to be fully seated in then? I understand that this screw controls the amount of air-fuel mixture going into the engine. So by loosening the screw, am I increasing or decreasing that amount?

id say rgrinder is right, pull it apart and clean it up and might aswell do a rebuild on it, can of carby cleaner and im sure someone here would have a rebuild kit. i used to have the same problems but i just changed to a 32/36 and removed all the problem instantly

The one you circled is not the pilot screw.

The idle-mixture screw is not supposed to be in all the way. It's supposed to be a little out. Turn in (clockwise) to lean the mixture. Turn out (anti-clockwise) to richen the mixture. Turn it as lean as possible that still returns a good idle.

If you tighten it all the way in, and the engine still runs, something is wrong. Conversely it turning it out a long ways doesn't have an effect, something is wrong and calls for careful cleaning.

Dirty carburetor exterior is OK, and doesn't cause problems -- unless the air jets get clogged. But those are under covers or under the air cleaner flange.

Idle speed screws



Idle-mixture screw

http://datsun1200.com/modules/mediawi ... tle=Carburetor_Adjustment

The arrow points to the Primary Slow Jet plug. It must not be loose.



If loosening this makes it run better, something is wrong. Tighten it, than adjust the mixture screw. If you cannot adjust it correctly, then there is likely an internal problem (not getting enough fuel). You can remove the plug, then spray down the hole. It should come out inside the bore where the idle mixture point is (look down the throat with a flashlight). Also it should bubble inside the fuel bowl. You do not need to remove the carburetor to do this. Also spray through all the holes in the jets to be sure they are not clogged.