So I just completed my first rotary rebuild today on my 79 12a. I had to get some used rotor housings that were usable as mine were totally gone. The ones I got are from an 81-85, the engine went together just fine and the header gasket and stuff fits just like normal but neither my 79-80 intake manifold or my 81-85 intake manifold fits the damn thing. The 79-80 leaves a huge gap at the bottom of the intake port on the intermediate housing and will not go flush with the engine and the 81-85 just wont go on all the way but the 81-85 doesn't fit my carb anyway. So I was wondering what I should so and if there even is an intake manifold that will fit this setup. I appreciate any help and look forward to hopefully getting a solution.

 

lol wut?

Post some pics, man.

 

The hole below your intake on your intermediate iron needs to be filled in, quicksteel, jbweld, devcon etc

And your carb won't work with the intake? Thought all first gen carbs from the factory were the same?

 

I'd use the 81-85 intake and not fill the hole and figure out why there is a gap. Something isn't right.

 

So it is much harder than I thought to take pictures of the problem I am having but here is my best shot. First three pictures are of my original 1979 12a intake manifold not fitting properly and second three pictures are of my 1981-85 12a intake manifold not fitting at all. I know it took me a while to get these pictures up but hopefully this can show my issue and maybe one of you guys have had or heard of this issue before and have a solution. Thanks in advance for any help you can give me!

 

You probably have a 13B manifold. Measure the distance of the holes at the rotor housing studs. You will see 12A is 12cm and 13B is 13cm. Mazda really did make it easy for us.

 

Yup, sure enough. The guy I bought it off of listed it as a 12a intake but just measured it and it is like 13.5 gap and my 79 manifold is 12.5 gap between housing studs. I don't have a very good way to measure in CM but that seems like the right difference that you mentioned. You know anyone selling an 81-85 12a manifold by any chance?

 

Make sure the next one is a 1981-1985 12A to cover the extra port.

 

Just wanted to update this thread, thanks to Jeff20B for the information regarding the distance between those holes. Was able to have an eBay seller measure it and got one that fits correctly now! I can finally finish my rebuild and it the car running again. Thank you all for your help!