Xavier8

After acquiring an 85 12a engine a month ago, I have finally gotten it working in my british car, but got a surprise today when looking for vaccum leaks, big streetport! The RB intake manifold and engine have been streetported (or maybe more), but a stock gasket had been installed that cut into over half of the intake ports. I cut the areas away and now the car will kindof drive with its brand new RB holley 465 for a NON-ported engine. I didn't know the engine was ported when I bought it.
My question is, can the jets be changed to make the engine work better on a ported engine? What jets are people using? Will the 465 be adequate? The holley currently has 45 jets I believe from RB.

kettlman

iTrader: (2)

i'm runnin a holley 650 on my street port. with 63 jets. although i get more air flow. don't know if it helps any.

heb09

I run a 465 on my BP, and NO its not to small. I actually was running WAY to rich before I had it jetted few weeks back now. It depends on the size of your port.

Xavier8

can you give me an idea of the jetting, so that I can acquire some? I figured that a 12a probably didn't need a huge 650, just some jet changes to run well. This will all be trial and error for me.

Crit

iTrader: (6)

Aaron, the 465 is more than enough for the 12A. I'd say it's too much, even, but nobody with 12As ever asks my opinion. RB nearly the only shop that deals with both Holleys and rotaries, so I'd give them a call for jets just to see what they say.

Xavier8

I really need to get some jet values before I spend 5 bucks a pop in trial and error. I am sure that someone is running a 465 street port that they had to rejet to run better. Thanks kettlman, I may have to use that as a baisis and start at 60 and buy in increment of 2 from there. Anyone know what they come with stock for a street port RB?

Rx7carl

Too big. Try 49's. Thats whats in the 465 I got off someone. Its a paperweight, I just bought it to study it. Its a true RB holley.

Snapshot

You should be more than happy. The Holley you have will be great! Don't give up & you will be amazed how quick your machine is compared to stock. Adjustments are multi level - need someone w/ experience to make you happy & not fry your motor.

Wankelguy

How do you know the internal port openings are enlarged, have you had the motor apart?

Xavier8

actually, have not had the engine itself apart, but the intake ports and the RB manifold have been enlarged and port matched. I found out when I took the intake manifold out and found a stock gasket covering more than half of the intake ports. I cut out the areas and reinstalled.

Xavier8

Wow, racing beat is not any help when it comes to carburators. I was hoping for any help from a quick phone call, but I got nothing! I am going to buy a 49 and 53 and try both, and then decide where to go next. 10 bucks of experimenting, but at least I might be able to richen the mixture alittle and drive the car. Still would love any help from knowledgable folks. Thanks.

Rx7carl

Try calling mazdatrix and asking. They are a bit nicer about fielding qusetions from the general public.

Snapshot

Hey, just try the set up you have unless you are a rotary master. The carb jets are minor. Be happy.

Xavier8

Thanks a bunch to people who gave me some specific numbers. I went to Barnetts and purchased a 49, 53, and 57 jet set, along with the reusable gasket kit. I got the idea while driving to my garage to look to see how big the jets are in the other holley I have lying around in the garage. They were 58s. I decided that since these were free, and I could return the other if I didn't use them, I swapped the RB jets (which turned out to be 49s, thanks RX7Carl for at least a number to start from!!!) with the 58 jets. Wow, engine woke up, and after a half turn of each of the air bleeder screw, a perfect idle and decent throttle response. These jets are slightly too rich, as they produce a miniscule amount of black smoke when revved quickly, but they removed me from the lean zone. Engine temps dropped considerably, and the exhaust pipes stopped glowing orange!! A quick recheck of the iginition timing proved that the timing was set at 0 degrees exactly, and a tooth later and some small movements, timing is right where it should be. The engine is much more responsive, I just have to get used to revving the little british car to 7000. The stock motor would only pull to 5500 rpm. Temp sat at exactly 180 at all times, idle around 1000. Still needs some tuning, but she is much better off than before. When she has any warmth, engine starts the first time with no added gas.