So I installed a 1/2" phenolic spacer between the carb and the manifold. Real RB carb, and obviously manifold.

Car would not stay idling at all, just died out.

Took the spacer off and its fixed.

Check for leaks with the spacer installed and came up with none.

Spacer is a 4 hole, which I thought would be good, as the manifold is 4 hole.

What I suspect the problem is, is that the bottom gasket (manifold to spacer) is not a 4 hole gasket, rather an open type. Guess this is screwing up pulses and what not, letting all 4 ports mix in a very small area (the thickness of the gasket between the spacer and manifold).

So with a bit of reading I am now more confused.

Many people have said to run a open type spacer and let the pulses mix, as well as help atomize the fuel a bit more. But many are referring to a 6 port rather than a 4, but I defiantly read a post or 2 about a 12a.

I am going to pick up a new 4 hole gasket (so now the top and bottom gasket are 4 hole), and see what those results yield.

Any pro/cons to running an open vs. 4 hole? The carb has the relief modifications cut into it by racing beat to do what ever it does. So if they designed it that way, why change it. But can help but wonder if the open style is any better, or has any advantages/disadvantages.

Thanks.

 

I have the open type spacer , same engine 12a bridgeport. It runs fine, I don't know if there is a difference, it was on it when I got it.

 

where does your engine idle without the spacer? have you tried adjusting it with the spacer on?

i believe i have seen the user Peejay touch on this very subject quite a few times. i would suggest going back through the threads you searched and find his posts on it.

i think i also remember Jeff20B spending some time on idle experiments in this thread: https://www.rx7club.com/1st-generati...-twist-942480/, but as the title states, this is a half-bridge so keep that in mind.

 

My half bridge also had a real separate runner manifold and an old school Nikki that could run on a manifold like that. All the later Nikkis came stock on manifolds with a channel connecting the primary and secondary ports together which increases vacuum signal and improved idle quality. This was not what I was interested in using on a half BP for obvious reasons. I wanted actual separation, as much as possible.

The result was fine, for what it was, but I find these days BP and half BP is dumb for the street. I prefer 74 spec ports and a channeled manifold. It runs a lot better and you actually want to drive it compared to just thinking you want to drive it. And then when I want power, I put a boost prepped Nikki on it and add a turbo. Works a lot better and makes a lot more useable power than any kind of BP.

 

You need a 4 hole gasket top and bottom because the RB holley carbs from them are designed to work with the individual runners. Open plenum with that carb will cause you all sorts of problems. Most people that run an open plenum modify their own holley carbs which I have done many times. The RB carbs are really great they respond well when adjusting them and are very drive able on the street. Only downside is the price but I guess you pay for the research and work they have done to get that carb working well with a rotary.

 

Thanks for all the replys.

The additional 4 hole gasket solved the problem.

Car idles as a bp should! Brap.