Thinking about goin carb
 

I am thinking about goin carb on my 13b 6-port.. i have a RB header strait through exhaust, S5 rotors in my S4 motor, removed emmissions, ps, and ac, and removed 5/6 port sleeves... i was wondering what would be needed for me to run a carb.. like what do i need ect.. also what size carb? vac or mech. advance? DP or single feed? any aditional info and results of this and pointers in the right direction would be really apprieciated. Thanks
Dave

First off, I don't know a whole heckuva lot about carbs. That said, there's a few things I do know -

You can't just get a carb from Summit or something and put it on - rotaries are really odd as far as carb settings are concerned, and it's best to start with a carb that's already set up or at least close.

You're gonna spend some serious money to go carb, too. Check out Racing Beat's site - I think they have a 6-port 13b carb setup. I'd also ask around in the 1st gen section - they're typically more handy with carb knowledge.

Dale

You would want to get a Weber or Dellorto already modified for a rotary and preferably one with the proper jets. Racing Beat makes an upper manifold that lets you bolt to the stock lower manifold. My carb is a Weber 48DCOE off an older Formula Mazda car. It runs so well we are afraid to rebuild it. We have tried to duplicate the carb(same jets, choke, emulsion tube, etc...) but have never got one to run as good as this one. Try www.thepartstrader.com if you can't find anything for sale on the forum. Just remember It might be cheaper to get a used haltech than a good working carb setup.

How do you like it? How noticeable the HP/TQ is? I know they make a LOT of difference, I've seen it, but haven't ride on one :(

You will need to disconnect your current in tank fuel pump and get a lower 6-7 psi 60-80gph fuel pump (inline fuel pump). Then you are going to need a distributor (out of a first gen most probably out of a junk yard or buy a rebuilt unit at a local car parts store). Two coils (for example two MSD blaster coils). A fuel pressure regulator, and fuel hose to route the new lines. I will be going with the Webber carbs, but if you do not know how to tune them you can buy a book on how to tune Webber and side draft carbs, I believe the book is made by SA publications. You can buy it at any muscle car performance parts store like Vic Hubbars, Summit Racing… Have fun.

Re: Thinking about goin carb
 

Yup, RB has the upper manifold that bolts to the stock lower manifold (you might get the 5&6 ports to work). Atkins also have a kit, and I know there is another palce but I just can't remember the URL :(

why go to a first gen distributor? The spark side of the engine shouldn't be affected by the fuel side. Or am I wrong?

An aftermarket fuel pressure regulator is all I would recommend for the fuel system mods. I've converted a couple EFI vehicles to carbs and found that the electric in tank pumps worked better than trying to add another piece of junk in the lines. The fact that the EFI pump will be cycling more fuel ensures that you probably won't vapor lock either.

I've heard about this, people running a carb with the stock ecu running the fire side...........

Anybody?!?

Jimmy is right. What I did was get a brass T fitting for the fuel line coming into the engine compartment. Route one side to the return line and the other to the carb. Put the fuel pressure regulator and an inline filter before the carb. I've seen this setup work on a car without the regulator but I wouldn't suggest it.

This is on my FP car so I don't know how long the pump will last if driven daily. Probably the same as a FI car but I'm not sure.

KNONFS - This carb was on the SCCA Alabama Region top CSP(1st gen RX-7) car about 7 years ago. It won the points battle two years in a row. I got to ride in the car and was extremely impressed with the power. They had put a stock S4 6-port engine in it to replace the 12A. It really pulled hard. I think the biggest improvement over the factory FI is eliminating the AFM. A properly tuned Haltech(or whatever EMS) will deliver the same performance if not better. The reason I'm starting with the carb is a friend loaned it to me till I can get all my FI parts together.

I agree with you, but the stan alone itself is close to $1100 at least plus the tunning. Atkins has a webber setup for $700. Not that I'll be going the Webber route, but who knows what might happen in the future ;)

HOLLEY 650 CFM.. RACING BEAT OR JAY-TECH 6 PORT INTAKE...JAY-TECHS ARE RARE THO.. AND U WONT BE ABLE TO FIT AN AIR FILTER ON TOP CUZ OF CLEARANCE(BUTWHOCARES,HALFOFTHECARB'D7'S DONT USE FILTERS) FUEL REGULATOR.. U COULD USE THE 1ST GEN DISTRIBUTOR.. THO MY COUSIN USES HIS STOCK S5 IGNITION...IM WAITING FOR MY REBUILD TO GO CARB MOST LIKELY... MY COUSIN RUNS HIGH 13'S LOW 14'S WITH THE STREET PORT 13B HOLLEY SETUP.. AND HE HAS A 90 AND I HAVE A 91 BOTH NA'S OF COURSE AND HE SMOKES ME BAAAAAAAAAAAAD.... I THINK ALL THAT HP COMES FROM NOT HAVIN THE AFM TO RESTRICT ANY AIR FLOW.... ALTHOUGH SOME PEOPLE DONT LIKE CARBS BECAUSE I ADMIT.. ITS OLD TECHNOLOGY.. AND WE HAVE EFI NOW.. NOTHING PULLS LIKE A CARB SETUP ON A NA ROTARY...

oops sorry for the caps....

FI is by far the better of the two methods of fuel management, but it's also far more complicated and expensive to fully realize an engines potential with it.

For the cost of the fuel injectors alone, I can buy a carb set up for my engine and make the same power of a dialed in haltech. (or whatever)

The carbs won't get the gas mileage because they don't know when the engine is under load or not, just that its pulling "X" amount of air at the moment. But, I can buy a lot of gas for the added expense of all the additional stuff needed to make an aftermarket engine management system work on my engine.

You can use the factory intake. Just strip the emissions crap of it. You already have the fuel injectors, fuel rail, throttle body, etc...... Pull the AFM off it and put whatever round air filter will fit on the intake tube thing. Tuning it properly is no different than properly tuning a carb. You go pay for some quality dyno time. I think tuning the stand alone EMS is probably easier. If you want the change the jets in the carb you have to shut the engine of and maybe let it cool down some. Then remove the jet or whatever to make your change or at the minimum twist a screw while the engine is still running. With a stand alone EMS you can sit in or beside your car, goto a certain screen and change some numbers to fatten or lean the fuel at certain rpm's. To me its just easier than getting under the hood again.

Sadly it all comes down to a money thing for me and probably many others so you have to get what you can afford.

Holley carb kit - $800
Can you use the carb kit and retain the EGI computer for spark? I'd imagine it would be unhappy but I've never tried it... so let's assume yes.

Malpassi regulator (allows use of stock EFI fuel pump) $130
-OR- Holley pump and regulator ($90) (this requires removing the EFI fuel pump and fudging the pickup with some tube, is your time worth saving $40?)

Guaranteed to fail emissions - variable cost (swap back to EFI every two years?)

No matter how you slice it you're almost at $1000. Fairly sure you can get a new E6K for a little more. Heck you can probably get a used one for a bit LESS than the cost of the Holley setup now that the new Haltech system is coming out and people will upgrade.

Should be able to find maps for a 6-port online.

Atkins sells the Weber kit for $750, or you could pay an additional $245 and get their MT8 EMS. However, the carb kit is much better if you are the type of person who likes changing out jets and spending several hours retuning the car every time the weather changes. :D
http://www.atkinsrotary.com/fuelinj.htm

480cc injectors won't make the 260hp my engine is capable of... I don't think you'll even try to argue this one.

So at a minimum I need a stand alone ECU ($1100) and 4 injectors ($500-900) and larger fuel pump ($150)which puts the cost of retaining FI a mere $1750-2200.

So how is it that the $750 carb setup is more?

http://www.rceng.com/technical.htm#WORKSHEET
480's look about right to me.
(Stock fuel line pressure is 34-40psi, and BSFC is about 0.5 stock but can get down to 0.45 when tuned well with an EFI)

However, if you really want a carb, then go right ahead and get one. It's your car.

260hp? going bridge ported then?

480? Stock NA injectors are 460cc/min, and can make ~260hp @ 85% duty, but that's definitely their limit unless you increase fuel pressure. A pair of Turbo 550cc/min injectors in the secondary positions up this to ~290hp, which is strictly PP territory anyway.
If you're making 260hp, I presume your engine's bridgeported? What fuel system are you using? You can get ECU's for less than that (I've seen E6K's for ~$1000 and Microtechs are even less), and if you pay $500-900 for a set of 13BT injectors you're an idiot. :rolleyes:
Whether you go carb or EFI, tuning costs will be similar (personally I think EFI would be cheaper because it can be tuned quicker), and aftermarket EFI will always outperform a carb (and I don't mean just peak hp!). If you're spending all that money, why not spend a couple of hundred more to get a vastly superior system?

My car is an 85 gsl, and i have a carb. Just a warning, they are a pain in the ass.... I would kill for EFI.

I just love a carb vs. FI debate.

If 4 injectors cost $500-900 just buy a wrecked TII and sell some parts of it to recoup some money, keep the injectors and send them to RC Engineering for cleaning and so forth. Thats what I did. Bought the unwrecked but not running 87 TII for $800(bad wiring problem) I sold some parts for $500 +/- and keep what I thought I would eventually use. I could have easily broke even but I gave the engine/transmission to a friend for his project. www.rotarymiata.com

Carb's not a pain in the ass, it just usually costs a hell of a lot less. Once it's tuned, you're golden. (The same can be said for EFI) If you're starting with a carb'ed car then it's much cheaper to stay carb than it is to convert to EFI.

HOWEVER, when you're starting with an EFI car, it only makes sense to go standalone EFI vs. convert to carb. Carbs are great and will get you 90-95% there, but if the cost is so close as it is in this case, why NOT go standalone?

Modified Bridge port actually. Rather than cutting the bridge open I'm swiss cheesing the area the hole would be in with a drill. Should be more stable for vibration and much easier on the corner seals. Should be a fun 10Krpm motor.

So why are all the turbo guys running 1000cc injectors to make 260hp? If I could get away with 100 bucks in used injectors and a SAFC and still make my power goal I'll keep the FI.

uh...

you're better off making the one big eyebrow than cutting a buncha little holes.

i don't see any turbo guys running 1000cc injectors to make 260hp! unless they're running only TWO injectors, or they're complete dumbasses...

I've got one for sale. PM if interest or email.
https://www.rx7club.com/forum/showth...hreadid=105994
-Mark

Hey personally I would stick with fuel injection, i had a 86 gxl that i did carbs on and it made it alot slower, i first went with the 45mm webber dcoe side draft and i lost at least 15hp from stock. then i went to the 51mm sp webber side draft and i was a stock horse power as normal n/a. it is not worth the money in my own oppion. i had full exaust and all the weight reduction. it cost me $2000 to get everything plus tuning it and stuff.

Not cutting, drilling then chamfering the holes so there isn't an edge. (and I'll bevel the back of the holes too)

I'm going this route because, I don't like the idea of my motor blowing up when vibration and time take out the bridge and everything goes with it.

I do realize that I won't flow as well as a true bridge port, but I can live with that for the longevity gained.

Because they don't know what they're doing. The stock 550cc/min Turbo injectors are capable of flowing enough fuel to support ~300hp if fuel pressure is maintained. Those people who are making less than that and think they need bigger injectors are failing to relise it's the stock pump that can't keep up, not the injectors.

i have installed a carb on a 86 and used the factory ignition without any problems

As did i. . . I got my weber sidedraft setup (w/ racing beat upper and fuel crap) for $450:D

I also used the stock ignition but it limits my performance
 

I recently converted my fuel injected S5 Motor in my S4 1988 RX7 Convertible to a 600 CFM Street/Strip Holley Carb.

I wanted to go with a Weber 44 or 48 IDA Sidedraft setup since there is more power to be gained above Stock Fuel Injection. This was a suggestion by Carlos Lopez of CLR Motorsports Miami.. I was desperate to get my ride back on the road so i opted for a transitory option in the meantime. Charlie of Turbo Clinic suggested a Holley Carb and I wish I would have waited for the Weber.

My girlfriend hates the fumes and odor that the Holley puts out.. also I have noticed that the Holley is a good carb for straight aways but not for cornering or curves. The odor with the Holley is quite pungent.

The Weber setup eliminates any bogging on turns, slopes, hard cornering and curves.. it's actually an all around better option for the FC. Back in the early 80's I used to race a 1969 VW Beetle in NY that had 48 IDA webers, a Hot camshaft, and other goodies and was doing 10.69 in the quarter.

When it came to the fuel pump and fuel pressure regulator argument. Here are the pros and cons..

Normally one would think that going with a Holley Carb setup would require that you replace the stock fuel injected fuel pump that creates more pressure close to 40 psi because at that rate it will blow out the gasket in the float bowl. It happened to me and Charlie's mechanics came out to rescue me and Jonathan along with Steve did a great job of getting me back on the road. Charlie had the Holley fuel pressure regulator P/N 12-803 which i paid $33.00 separately for out to its maximum adjusting position. Keep in mind that i am using the stock fuel injected fuel pump that came with my vert. His suggestion was to purchase the Holley "Blue" fuel pump P/N 12-812-1 for the low price of $120.00 and another $80.00 in labor to hook it up. I also had a liquid filler Russell Fuel Pressure gauge $24.00 installed with my Holley setup that unfortunately is on there for looks because it doesnt register anything at all as you will soon find out as you read on.

Carlos Lopez had a solution for me that would eliminate the problem without having to replace the fuel pump which would be expensive at this point in the game. I gotta tell you that this man knows his shit really well dealing with RX7's and Rotary Technology. He suggested replacing the Russell fuel pressure gauge since it was not registering or reading. One way he came to that conclusion is to attach a tool that he has to correctly adjust fuel pressure that is made of an older version VDO gauge and fuel lines attached to it. Then what he did next was to remove the Holley Fuel Pressure regulator and its place install a Malpassi (Made in Italy) Fuel Pressure Regulator that is shaped like a flying saucer and with his gauge he was able to set the pressure at 6psi. I was able to keep the same stock fuel injected pump that came with my vert. Another person that was in agreement with this setup is Dennis DeSilva "RPM Doctor" forum name of High Tech Auto. Carlos got my new reborn FC Convertible "Jezebel" running right... all we had to do is just use the Malpassi fuel pressure regulator that retails for about $85.00 or so.

All in all I made out pretty well and it goes to prove to the old saying: "You get what you pay for "

Carlos Lopez is a genius at what he does best and this man has a world of knowledge and in the next couple of weeks I will be getting the Weber 48 IDA Carburetor and Manifold from Racing Beat. The Holley carb is a good setup and its simple to actually do the conversion so I will have the Holley Carb up for sale within the next couple of weeks as I will be going with the Weber setup that Carlos Lopez suggested to begin with. I will also be going with a single turbo setup and he will be the person to build this motor together.


Malpassi Vs. Holley

I recommend using the Malpassi Fuel Pressure Regulator instead of the Holley. This is a pic with the Malpassi Installed .. this pic shows the stainless steel braided lines and of course the Malpassi fuel pressure regulator. This is pic is just to give you an idea as to what the conversion looks like.. this Holley Carb and manifold set up will be up for sale soon. I expect to get what i paid for .. this system was installed just last week so it is still relatively new.

https://i3.photobucket.com/albums/y7...frontview1.jpg

Most of you are talking carbs vs EFI for the sake of more power. I just want something less complicated and easier to work on. I love my '89 vert when its running. I've had it with fuel and electrical issues. Is it possible to use the intake and carb from a first gen car....without major modifications? I know where I can readily find one of those.

Yes. You just need to make an adapter (or buy from Mazdatrix) to fit the intake manifold to the longer block. Keep in mind you still need to take care of fuel (reg, pump) and ignition. And the major pain in the ass factor of tuning a carb to work well under all circumstances, when the stock EFI does it automatically.

OK, took a look at their site. Will have to call them tomorrow. So if I go with a carb, distributor, new exhaust, will I have any use for the ECU? Will all the gadgets and gauges in the interior still function?

You'll have no use for the ECU.

Sounds like a lot of trouble to go through for a downgrade. :)

Its not that complicated...
 

In my setup I dont have a distributor... I just have the Holley Carb, Manifold, Malpassi fuel pressure regulator... and the stock crank angle sensor with the spark plug wires... the ECU is still in tact and I have some really nice HP

Now , I will get the distributor which will do away with the ECU for the most part and it will work fine.. better response and less problems...

the gadgets and gauges still function...
https://i3.photobucket.com/albums/y7...frontview1.jpg

Talk about bringing a thread back from the dead... To think if i still had this car.. damn... hehehe i just think its funny that i made this about 3 years ago and its still alive..
Dave

It was dead for a little bit....

Though, carb sucks..... ;)

i have a sidedraft weber dcoe 45 carb. how much of a gain in hp do you think it would make if i put it on my 85 fb

I also have the 45 DCOE Weber
 

That is pretty cool...I would like to see your set up ... I have a 2nd gen vert which you know is heavy... but with the 45mm Weber I have greater low end torque and with the 6th ports vacuum actuators top end as well... i like it.. check out my pics


http://i3.photobucket.com/albums/y71...RMOTOR1037.jpg

http://i3.photobucket.com/albums/y71...OTOR2LH041.jpg

http://i3.photobucket.com/albums/y71...DOOROPEN08.jpg

Preacher, I too have a convertible that I recently converted to Carb. I have the Racing Beat setup. I am in the middle of tuning it and am finding it difficult! I wanted to know if you still have the gas odor problem with the weber? Any cold star issues? I am thinking of switching to the weber. Also, where can I get a malpasi pressure regulator? Thanks for the help!

is that a rising rate fuel regulator?

Why downgrade to a carb?

We've covered this (in this thread in fact).

Holley running great! What timing are u running?
 

After properly ajusting the accelerator pump linkage (had to do some grinding to gain clearance) the Holley is running great! I have a Malpassi fuel pressure regulator on the way and I am going to eliminate the Mallory fuel pump that racing beat recommended and revert back to the stock fuel pump. When I am finished the break in period I will bring to the dyno for tests. For those that are running carbs what timing are you running with the leading and trailing ignition?

I run a carb on my camden. My buddy went from efi to carb, then back to efi, then carb again and finally back to efi. The efi was by far the best setup for a stock or streetported 13b.

And that's coming from an old dog that knows little about efi and is capable of working on almost any carb. I'd stay efi!

Hey guys,
I have a 13B Nikki carb on a T2 block, 1st gen dizzy and 2GDFI setup. Can't get them damn thing started...is there something special I should know about setting timing?
Thanks,
Owen

Carlos Lopez of CLR Motorsports did my 45MM weber carb setup and the sidedraft setup is by far the best .... no problems... he used the stock fuel pump and the best Fuel Pressure regulator: MALPASSI

http://i3.photobucket.com/albums/y71...7/IMG_2775.jpg

Setting the timing in the middle of the adjustment should be fine for starting as long as you aren't one or more teeth off...Does the engine want to spin backwards when you crank and go against the starter?

Do you have spark? What about a little shot of ether into the carb...does it fire then?