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Chiefbauske

New carb new problems

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Installed a new shitachi carb on my Datsun/Nissan Sentra and it’ll idle for about ten seconds then it’ll bog down. I’ve adjust the idle screw but can’t even find the air to fuel screw. When I plug up the intake on the car it idles fine but the moment I take it off it bogs down. I’ve checked for vacuum leaks and can’t find any. I used the wd40 method and the engine didn’t idle and different at any of the vacuum ports. I was told to check the float level but on this new carb there isn’t a dot or notch on the glass. The fuel in the glass sits about half way. My carb base nuts are tightened as tight as I can get them. 

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You should fill out your profile to include the year and engine. This is an '82 or something? Where did you get a new carb?All that are out thee are Chinese knock-offs.

 

What do you mean plug up the intake? There should be no openings or vacuum leaks.

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It’s an 84 I got it off of eBay (bad Idea) I put a my hand on top of where the intake would be (so the top of the carb) and it idled fine. But the moment I take it off it accelerates like crazy. Wouldn’t that lead to one to think there’s s vacuum leak?  

 

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Top of the carb is not the intake (manifold) If you part cover the carb you are in effect choking or increasing the richness of the fuel air mix. Below the carb is the intake manifold and it has a vacuum caused by the engine drawing in air past the closed throttle plates in the carb above it.

 

I have yet to see an engine rev up from a vacuum leak in the intake. Extra air getting in would cause the mixture to be too lean.

 

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First of all is this on a warmed up engine with the choke plate open???

 

Do you have the idle speed screw turned down? Or is it holding the throttle open?

 

Is the throttle cable too tight and holding the throttle open?

 

 

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Cable is loose. 

 

I cant even find a choke plate on this carb or the original. 

 

And right now the screw is adjusted to where if I cover up the top of the carb (so the part of the carb that has the opening on the top) it idles at 950ish rpms (my tach is dead). The choke is electric I believe. I’m just now learning about carbs so if I don’t know the whole terminology feel free to fill me in. 

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L043Tu4.jpg

 

Choke closed

 

Qml955T.jpg

 

Choke open

 

Choke should close when engine is cold to help start. It has an electric heater that warms and opens it in 5-10 minutes, depending on just how cold it is out. If the choke is on or even part on the fast idle may be engaged.

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But it also is spitting out black smoke meaning it runs rich (correct?) I can’t find any other adjustment screwing on it beside the idle adjustment screw. 

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So again, is the choke open or not?

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I have no clue. How can I tell if there is no choke plate on it? Since I’m told it’s electronically controlled and all my wires are connected I would assume so.  

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 s-l1600.jpg

I see what you mean. I bet this is an electronic feedback carb? Later 720s had them. They use sensors including an O2 to monitor the fuel mixture. I wouldn't know where to start on those.

 

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