A few days ago I was getting gas after a normal drive and I turned the car on to drive off, it started for a second then turned off again, and then wouldn't crank. So we got it towed home and after a few hours I went downstairs to look at it again, now it cranks and even starts, but under 2k RPM it just feels like it wants to die.

I thought that maybe it was a vacuum leak, so we did the blow smoke into the lines to see where it's leaking out trick, but no smoke comes out. What else could it be? Does that trick even work on these engines? I guess we could try the carb cleaner trick, but will you still be able to hear the idle come up by itself if someone has to be in the car holding the gas?

Here's a video of it running, with me at first keeping it around 2k and then letting off the gas. Amazingly, sometimes it actually still runs at that incredibly low RPM.

IMG 2097 - Sendvid

 

Got any history?

How long have you had the car? Do you drive it often? Have you done "things" to it recently?

Seems like fuel delivery issues. Just from looking at the video. That encompasses vacuum (cause you need vacuum to pull fuel from the carb at idle), and idle fuel circuits.

 

I got it about a week ago, and I drove it everyday. It's stock when it comes to the engine, last thing it had done in the engine bay was a new alternator and new master brake cylinder. The rats nest is still there and it just passed 120k miles.

 

Check compression before you do anything else.


Really seems like you might have some trash in the fuel system. Most likely in the gas tank, but I'd still check the compression before I started dropping the gas tank to give it a good cleaning. Check the fuel filters; another words replace them.

 

Alright, I'll do a compression test. Something that happened today though is that it actually idled at 1500, still very roughly, but it seems to be able to idle once the engine is warm.

 

With any older unloved daily carbureted car, your fuel system has the tendency to get gunked up. After seeing some good compression numbers; I'd jump into cleaning the crap out of the gas tank, lines, and fuel filters. Toss a can of seafoam in the gas after you've done all of that. The seafoam will do a good job of cleaning out the carb.

 

So you got the car a week ago, probably filled it with gas. Drove it everyday and now thats its low on gas
you have issues? Does that kind of sum up your issue? I suspect it does. What was its history before you
got it and started driving it? I suspect its one or all of these things:

1. Clogged fuel filter from gas getting low and crud from the tank getting into the system.
2. Crud got up to the carburetor and has blocked tiny orifices and cause mayhem with cruise/idle circuit.
3. Big vacuum leak has opened up somehow.
4. Possible other things wrong but I doubt its compression but it never hurts to check it.

 

Did a compression test and the rear rotor is done, that's too bad. Thanks guys.

 

So you plan is to junk the whole car just because the engine, which is deceptively easy to change on these cars, is done? Or will you do the right thing and get another 12A or possibly swap a 13B in?

If you go 13B, I'd have to recommend against EFI. What you should do instead is get an aluminum plate from Mazdatrix and drill/diegrind it to allow your 12A intake manifold to adapt to your 13B. You should also look into hogging out the stock Nikki carb because they run better than any Holley or other carb options on these engines.

What I just described is exactly what I'm doing. I realize this is a lot for a beginner, but we all have to start somewhere. Good luck.

 

Yup, that's what I did. Cept I used a piece of 1/4" steel plate from Lowes. Although now I have some more money I want to put an RB manifold on my car and adapt the nikki to it.

I think going nikki on a 13B is an excellent option for people who aren't up to rebuilding their 12A. Just give the 12A to someone who wants it; don't just toss it to the scrap yard.

Depending on your exhaust situation you might have to make an investment. But if you have a set of headers as is you can cut and re-weld them so they fit a 13B.

 

I definitely want to rebuild the 12a or swap a 13b. I'd like to keep it carbureted too. I wanna daily this car, and the carbureted engines seem to be more reliable? It looks like there's more 13b stuff too incase I ever have to rebuild or replace things.

 

N/A usually has a longer engine life compared to turbo engines. If everything is factory stock; carb and FI are almost equally reliable. Swapping a FI system into an FB is obnoxious, and if you do you'd be better off just going turbo if you go to all that trouble.

 

Yeah I don't wanna swap the EFI into the FB, and I wanna keep it NA. I want it to be as simple as possible. You have to swap in an ECU or something right? How much power can you get out of a carb 13b? This is gonna be a street car so no bridgeport or anything, what would a mild port do?

 

If you want EFI you'd need....
An FC donor car; and lots of spare time
OR
A stand alone fuel system(ECU); and a throttle body and intake manifold and fuel pump/lines and 4 miles of wire. Then you'd need lots of spare time
OR
LOTS of money and someone with lots of spare time




Easier to do what Jeff was saying. Just keep the nikki and get a good keg. There is an adaptor plate out there that adapts your existing manifold to the 13B. That's the ticket because you won't have to mess too much with your fuel system other than tinkering with the nikki a wee bit.

13B 6 port (the N/A FC engine) engines are available relatively cheap. Because most people are after the 4 port turbo engine that has the lower compression rotors. A good running FC 6 port engine shouldn't cost much more than $400-600.

 

Do you have to get one with the transmission or can you use the FB one? I have the 5 speed. How much power can you get out of the 6 port 13b? I don't want to do a bridgeport or anything crazy because it'll be a street car, but maybe a mild port?

 

Do 74 spec ports if you are keeping the 12A. If you decide to go 6 port 13B, do not change the port timing at all. Only remove the exhaust diffuser wings in the exhaust sleeves as they can cause a restriction at higher RPMs.

Red this thread for more info on the 6 port 13Bs I've done. https://www.rx7club.com/race-car-tec.../#post12127759

The best 6 ports have been the ones with a hogged out Nikki on a 12A manifold welded to a 6 port flange, stock intake and exhaust port timing, only smoothing performed in the intakes and exhaust diffusers removed from the sleeves. RB long primary exhaust system and their spun aluminum air cleaner assembly. I also run DLIDFIS on everything because it works better than other ignition options.

The worst have been the ones that were ported out to 74 spec or bigger. The 6 ports have too much port area from the factory already. Increasing it hurts performance.

 

Your transmission will bolt up to an FC engine. You will have to elongate the motor mounts a little bit.

You'll be happy with a factory port 13B. Its not gonna rock your socks off but it will move along nicely.

 

Same issue here.

 

I would rebuild the 12A if it made sense. It's such a great engine! That is the true power plant and when built right they see might twice the amount of miles that a 13B does. I don't think any of us have ever seen a 2nd gen with over 300,000km and still running great -or 3rd gen? lol! I've seen FBs with more than that though(and probably on their way out soon but ****, they made it to 300,000).