Vacuum Ports on SU Manifolds

[bajcsi]

Hey everyone,

This is my first post on this board. Great posts on SU's and carbs in general. I didn't find anything on this, so if I am posting a question that has already been answered in the archives, I am sorry.

I have a 3.1L build that presently has SU's with Grose-Jets on it. I will eventually go to triples or throttle bodies but for now, this is what I have. In anycase, check out the attachment. See how there are two vacuum ports, one blue and one green? The next two? I am curious as to what they were for? Any recommendation on how to plug them? Are the NPT or some BPT? If not, I imagine I'll need to just drill and tap the holes and then plug them?

Thanks,

Brett

'77 280Z

[beandip]

I don't have a clue what someone has added these for, this a new one on me. You can just take the intake to a welder and have the holes filled or as you said tap them and screw in plugs or a bolt. As for your Grose Jets I have been reading for years in every venue not to use Grose Jets . ZTherapy would be a place to ask about them. Gary

[bajcsi]

Hey Gary,

Thanks for the reply. I rebuilt the carbs several years back with a kit from ZTherapy. I could not remember for sure which needles they were (SM, GrossJet, whathaveyou) but I found a packet the other day that said Grose Jets on them. Interesting. I'll look into it.

As for those holes, that is actually a picture of a new old stock manifold over at www.oem-surplus.com. I had originally thought that a PO had just messed with my intake, but apparently not. I'll look into it and post back. I imagine I'll just tap and plug them.

Thanks!

Brett

I don't have a clue what someone has added these for, this a new one on me. You can just take the intake to a welder and have the holes filled or as you said tap them and screw in plugs or a bolt. As for your Grose Jets I have been reading for years in every venue not to use Grose Jets . ZTherapy would be a place to ask about them. Gary

[Go240Zags]

I believe that is a 260Z manifold from a car equipped with the flat-top carbs. Legend has it they flow slightly better. I had a manifold, N36 I think, that has the same ports. They were blocked off with screws if I recall.

[DeesZ]

Here's a picture of what came on my mid-'73 mfg. date w/ flat tops (one of the few things remaining from her that rust did not eat).

[MrZ]

Hi sIR,

The blue one goes to the vacuum advance on the DIZZY. However, I'm not sure on the green one.

Hope this helps.