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OEM Hitachi Carb & Vacuum lines


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Need some help! I got my OEM Hitachi Carb rebuild, now I'm trying to put all the vacuum lines back in it's place, but I got stuck with this two carb ports. I know one of those ports go to the one the distributor advance line, but don't know if it goes on the top port or the bottom.

This is a 1978 B210 California emissions set-up. Thanks in advance.



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Vacuum advance port should be just above the throttle plate when closed at idle. There should be no vacuum advance at idle. However as the throttle opens the plate rises up to and above the port and  intake vacuum is felt. As the plate opens farther the intake vacuum begins dropping and at WOT there is almost none at the port.


That said, the vacuum port is above the throttle plate but the outlet pipe might be anywhere. Someone who has one would know.

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Thanks guys for the feedback. I posted the same question on the Facebook group. Some suggested to test which port creates a vacuum when the gas pedal is pressed. That way I would know which one is the vacuum advance port. 

I think I will do that this weekend.


Now my second question would be. What is the purpose of the port that is NOT the vacuum advance port?

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It is most likely another ported vacuum source to control the EGR. (exhaust gas recirculation) This is an efficient way to reduce peak combustion temperatures that cause NO emissions. It only happens above idle and at part throttle. At full throttle, the vacuum signal is so low the EGR is not activated.





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