Ok, so you know me. I'm out there helping people carb their rotaries in my spare time every single day.

Over the years of different installs, I developed a very well known prolific hatred of the 4160-4150 (Holley) 4bbl carb design.

This should probably be in the FC section, but I thought i'd share this here since it totally blew my mind.

Over the last weekend I helped a close friend swap a 300$ quick fuel vac secondary carb onto a cheap summit/JW intake manifold. Our intent was to swap in a 12A distributor, get it in time, and live with its crappy-ness while he learned about it for himself. (Like everyone else, he just didn't want to learn from MY experience).
Now, after I got everything installed, I had the harness all out of the way, but had not yet cut anything from the factory sensors or equipment or ignition.
I decided for ***** and giggles to start the FC on its factory ignition with my already sort of pretuned carb on it.
NO surprises when it started for a few seconds, then died. Repeatedly. The factory ignition was no doubt controlled by some of equipment we removed.

Now comes some stuff we can learn from.

I have a plethora of different gen parts lying around, and I was armed with a smartphone with access to the forums here so I decided to research what actually made the ignition work. I may not have found everything, but I did find a couple key things.
I wired the flow meter wide open, and reinstalled it. I reinstalled the TPS, and left it wide open as well. I plugged in the water temp sensors.
Attempted to re-fire. Success.

Car ran. Well. I was able to get his floats adjusted, idle speed to about 800 RPM, and a nice smooth idle. My understanding is that the ignition is at full advance this way, so its like a locked dizzy? I still dont know.

Now, this is the REALLY interesting part. The off the shelf vac secondaries wouldnt work without further mods, so I temporarily modified them for mechanical actuation. I then took the car for a drive, armed with my LM2 for data logging.
I took it down many of the same roads I tuned my own carbs on (of the very same like, in FB's), and I noticed a massive difference in the area of my biggest annoyance.
Cornering, braking, and transitional fueling.

I watched the LM2 dip well into extremely rich 9.8:1-10.5:1, in places where the Holley carb *always* will go rich, BUT the car didnt bog. It didnt even sputter.
With the secondaries wired to be mechanical all I ever got was about a .5 second delay from 3k RPM and then it would set full sail to redline. Again, extremely rich because it needs tuned, but NO bogs.
My FB's ignition systems would have bogged at those AFR's. It wouldnt have been able to return to idle after WOT at a mixture that rich. And it certainly would have stalled if I forced the secondaries open so early and dumped in that much fuel.
I drove that car hard, threw it into heavy corners, braked excessively hard, and tried provoking stalls with low RPM WOT. The ignition performed flawlessly.
It was like driving a different carb. The problems with that design still exist, but it wouldnt have been noticeable without the wideband.


My testing with the car isnt done yet, either. I'll be tuning this thing in the coming months, and were also hooking the flow meter back up to the carb via cold air piping just to see what that does. It's actually a very cool setup.


Anyways, is the FC ignition really this much better? Is there a way for me to make the FB ignition perform this well? I always heard that the factory ignition system didnt need modifications to perform well, but now that ive personally seen the difference, im shocked.

 

I own an fc with bw turbo ,haltech and stock fc coils. I also have seen 9.4 afr at.WOT without it breaking up.

 

I wouldnt have believed it if I didnt see it, seriously. It's incredible really. The next time someone asks me what mods to do to make their holley not bog in corners, im going to tell them to install FC ignition, lol.

 

Um welcome to direct fire, my friend. It really IS that much better.

Don't tell them FC ignition, though. There are better options for the 1st gen. I use DLIDFIS. I can go from pig rich (beyond 10 AFR) and back to idle without any problems. It handles boost a well.

I would not run stock through the cap and rotor 1st gen ignition on anything I intended to actually drive. Same thing with a stock Nikki and its tiny 20mm venturis. I just can't stand the way they are stock.

And now you understand why I've been a proponent of direct fire ignition for years. Welcome, friend.

 

+1 The ignition is the weakest leak on a 1st gen, followed by the exhaust and then the carb.

My ignition can start a flooded out rotary in maybe 3 or 4 tries no problem.

 

I really don't like having 2 plugs not using the dizzy and 2 using it though. Any way to get all 4 direct?

I seriously may consider efi just to run a proper coil on plug ignition lol

 

lol, thats a rabbit hole!

the FC ecu's compute the fuel injector duty on the fly, but the timing is actually a Map based on RPM and load, with a couple of corrections for water and air temp. there is also an idle map, that is fixed at -5 and -20.

the FC ignition doesn't do anything radically different than the distributor, but where the dizzy has ~20 degrees of capability, the FC has 48, so it can run larger curves.

if you wanted a low buck solution you might put the FC TPS on a bracket, and then put another TPS in place of the AFM. the AFM just delivers a 0-5v signal, the same as any other sensor, and it basically follows the throttle position, give or take. the FC ecu also bumps timing at idle for AC and PS inputs, so it could be pretty flexible.

price is right! and the S4 ecu doesn't care much about not using input/outputs

 

So with it set up the way it is right now, would if cause any problems? It runs like a champ, and ita not even tuned. Am I good to leave the AFM wired open and the TPS open too?

 

should be, i couldn't find the S4 timing map, although its been posted. they have been, and i do have them on another computer

in the mean time, try this https://www.rx7club.com/2nd-generati...ck-ecu-943159/

https://www.rx7club.com/engine-manag...etter-1089664/

 

So the timing is locked at full advance like I have it or is it going back to the -5 btdc idle map? Does the tps tell it to go to idle map?

 

Subbed as I am running a RB Holley on my 79.

 

I think the lesson here is if you're gonna run an RB Holley, you gotta also use direct fire.

 

Yeah it seriously masks a ton of problems. Doesn't fix them, but hey. If it takes a wide band to see the problems, and is otherwise unnoticeable, I'll call that a solution.

 

All of my Nikki carb testing over the last two years has been done with direct fire. If the carbs do have problems, they're certainly masked. That's why it was good to have you test my recommended mods on your carb and your ignition. I'm glad they worked out as well as they did (better than any Holley). It's always good to get data like this.

Now the next thing you should do is look into installing DLIDFIS. Don't bother with all the crappy FC EFI garbage just to run their direct fire in a 1st gen. It is so not worth all of that Rube Goldberg crap cluttering up your nice engine bay. DLIDFIS does a better job, honestly, having a dedicated ignitor for each coil and each leading spark plug, and gets to use the stock dizzy!

Oh and it's ok to feel weird about the three open spots on your cap. If anyone asks about them, just speak to them in a Tim Allen voice saying, "I rewired it!"

 

Carbs aren't 100% perfect 100% of the time, but neither is EFI. They just throw fuel at it and hope for the best (almost all the FC exhaust ports and turbos I've ever seen are pretty black inside). Plus we know the stock 1st gen ignition isn't the best. So yes I'd call direct fire a solution.

 

Here is another reason to not use the FC ignition. I've seen the wear pattern on FC spark plugs myself. https://www.rx7club.com/2nd-generati...plugs-1098274/

 

Interesting link on the 2G spark plugs. I'm using the 2G coil as my leading coil now on my DFIS
would that alone cause this? Now I have to pull my RX8 plugs and see what they look like.

 

look at the thread again, the coil HAS to work a certain way, its electricity

 

Update on this. Finally got around to tuning this thing. I installed a carb hat and flex duct right to the factory AFM and the carb actually pulls the door open just fine on it, so for now I'm leaving it how it came from the factory.

This setup continues to impress. I jetted it a littletter today, did some top secret mods to the fuel bowls, and changed the air bleeds to one of my known good arrangements.

I pushed it extremely hard in corners, and especially braking. It's dammed near flawless and I haven't even started data logging for the fine tuning.

I would seriously recommend this setup to sone one who wants a snappy, and simple FC.

 

I have never gotten any of the RB carbs to run this well so easily.

This is literally an off the shelf quick fuel "slayer series" with some very light mods.

They go for 319 bucks, and are all aluminum and come factory with down leg boosters.

Lol I'll do a write up for this for anyone interested. Was extremely cheap and easy to do.

 

for AFR's the FC runs whenever is best at idle, under 25% throttle between 1200-3500rpm its running 14.7:1, and then @wot its about 14.2:1 at 2000rpm and goes to 12.2@4000, and then it leans out to about 12.6 by 6500, and then it goes rich.

if you're in that ballpark, timing should be pretty spot on

 

Please do a write up, don't hoard the knowledge. LOts of pics too and links to where
you bought them or to ones similar.

 

Teaser pic. And I have it tuned now. It's a lot of fun.