ThirdPedalNirvana

Hello helpful people!

My 12A 1985 GSL (all stock underhood) gave me some trouble yesterday. Everything was running fine, and then I started to notice pretty severe hesitation. I would step on the accelerator get nothing, maybe some bucking, or if I was lucky a sustained period of the engine making power for 2 or 3 seconds and then stopping again... UNTIL I got into the regime where the carburetor secondaries opened up, then everything would work fine! Drop down below 3000, and the car is barely drivable. Get it above 4000 with a downshift or some luck, and it pulled as hard and as happily as ever. I managed to "limp" to my destination, keeping the RPM's as high as possible, taching up to 5000 rpm every time I got moving so I could use the momentum of the engine if the engine hesitated.

My first thought was "this must be a fueling issue, because if it was ignition, it wouldn't run right at high RPM". I thought the Carb primaries were having fuel flow issues, and the secondaries were getting all the fuel they could need. Maybe the secondaries use one float bowl and the primaries use another? Maybe it is related to the accelerator pump, which I know is not working as well as it should? I got a tow home so I wouldn't be waiting for a tow truck in the middle of nowhere, and when I drove off the truck, the engine was running perfectly. Huh? If the carb had a mechanical blockage, I would expect it wouldn't "fix itself". All the nikki carb advice I found said "if it is running right, don't mess with the adjustments", and at the moment it is running right, so I don't want to touch the carb. But I also don't want to take the car out for fear of the issue starting again.


I spoke briefly to a local Mazda specialist. He told me that he was all but certain the problem was ICM for the Leading edge spark. He said that the trailing edge plug only fires above 3500 rpm, and so it would be working when the secondaries open, leading me to think the carb primaries were having issues, but actually I was getting intermittent spark from the leading plug, which, he said, was the only operating plug below 3500 rpm. Ignition faults make sense, since this problem is digital in nature: either the car is exhibiting the problem or it isnt. The hesitation turns on and off like a light switch. That, and everyone always says (about nikki carbs) that your problem is likely ignition, not the carburetor.


Can anyone corroborate this? Is it really true that the trailing plug doesn't operate below 3500 rpm? Because otherwise I don't want to start messing around with my ignition system. Has anyone else had a problem with the ICM's on their 12A, and were the symptoms and failure mode the same? I know that what can fail is the spark plug, the coil, or the ICM. Is there a way to check which component is causing the issue, or would the coil/plug fail completely rather than intermittently? What diagnostic procedure would you recommend?

Thanks!

GSLSEforme

That information is incorrect. When the car is started and running both leading and trailing ignition fire their respective plugs from idle to redline 100% of the time.
The only situation where this does not hold true is with early SA cars with thermal reactor that shut trailing ignition off on decel to keep reactor up to temp.

Igniter failure whether intermittent,heat related is more common as these cars age. Check your basics 1st before throwing parts at the problem. How old are ALL the tune up parts,cap,rotor,plugs,wires,air&fuel filter.
Ignition coils can be ohm tested,can be swapped,igniters can be swapped to see if the symptoms change and follow the swapped part(s). Recommend switching only one component at a time so you'll know which part changed things and focus on that.

Reading your post,have to wonder if it isn't a problem with fuel delivery.

t_g_farrell

iTrader: (1)

Dont use that mechanic, he's full of it. It could be an ignitor failure when it gets hot but since it runs at WOT on the secondaries I would think its carb/fuel issue. Check the fuel fliter first along with whats already been suggested.

ThirdPedalNirvana

Thanks GSLSEforme! It sounded plausible but I couldn't find any other sources to corroborate what the mechanic told me.

I am the 3rd owner of this car, I've owned it for 13 months. It has 255k on it with a reciept from Atkins for a rebuild at 190k. My first breakdown was from a clogged fuel filter, so I replaced that about 10 months ago. Air filter doesn't look bad at all but I could replace it (but wouldn't that have more of an issue ABOVE 4000 rpm than below?) .

Based on my visual appraisal of the car when I bought it the plugs and wires looked new-ish, I don't know how to ascertain the health of the rotor or cap, but I would expect issues with spark distribution (because I assume you're not talking about the iron core part of the rotor that activates the igniters) to be even more prevalent at higher RPM, ditto anything else with the electrics. The car ran great when the secondaries would open, terribly when it was just on the primaries. Of course since I got it home it's running fine, so I can't even diagnose the issue unless I risk getting stranded and use ANOTHER AAA tow.

If the car only exhibits symptoms at low RPM's and doesn't exhibit symptoms at high RPM's, AND the ignition system doesn't change its operation very much between low and high RPM's, can the issue I experienced possibly be an ignition problem? If so, how? Through what mechanism could an old ignition system result in flawless running and seamless power when under heavy load at high rpm but result in severe hesitation at lower than 3500 rpm? I don't want to start messing around with a fully functional ignition system if it can't possibly cause the symptoms I experienced.

The fuel filter is new-ish (I replaced it when the engine was leaning out, running hot, and stalling on me) and it looks clean to me, I can replace it anyway. But I would think a problem back at the fuel filter would affect delivery to the carb secondaries too. Once I started having this issue, I was about to get onto the freeway. I traveled about 10 miles on the freeway at speed in 3rd gear, above 4000 rpm the whole time, and not once felt the slightest bit of hesitation or bucking. The car ran perfectly. I struggled to get around once I pulled off the freeway and had to operate at lower RPM's, frequently stalling when I was trying to get going, and having to nurse the car up to a speed where I was above 4000 in 1st gear. So what on, in, or around the carburetor can I look at or check? Does the carburetor have a different float bowl for the secondaries than the primaries? I just don't know carburetors very well, except that everybody says over and over that Nikki carbs never need you do to anything to them, and if you mess with them you'll make it worse.

I know that there has been a persistent issue with the accelerator pump, which has never caused me to stall but creates a brief moment of hesitation if I jab at the throttle from idle. Could that be related?

Thanks!!!

ThirdPedalNirvana

I just saw a diagram of the nikki carb, and if I'm not mistaken, the float bowls are NOT dedicated to primaries vs secondaries, each bowl feeds one primary and one secondary throat. I'm stumped, guys what could be causing the secondaries to operate normally but the primaries not to get fuel? And how could the problem present itself in an intermittent way?

I want to be able to trust my RX7 again. I like taking her to work when its not too hot a day.

GSLSEforme

I don't know your skillset regarding working on your own car or if you take it to someone for repairs.
If you do not feel comfortable or don't have the knowledge you're likely better off finding a trusted mechanic that is experienced with rotary engines. The guy you referred to in 1st post...its not him.

If you don't KNOW how old cap,rotor,wires,plugs are that is a good place to start,the basics. These are all consumables like brakes,tire,batteries and each need to be renewed as necessary.
I understand car has a lot of miles and engine rebuilt and ran well til it didn't,so something changed. Your posts include several clues to the source of the problem(s)that a mechanic would follow up on and it is possible for a car of this age and mileage to have more than one fault causing your symptoms.

Nikki carbs are reasonably trouble free but at some point in cars life they will need attention. Your statement about the accel pump being inop is one of the clues. Your statement about your 1st breakdown being from a clogged fuel filter is another clue.
These carbs are not simple nor are they terribly complex. They have numerous passages in the castings,several jets and air bleeds for the primary and secondary circuits respectively.There is a primary float bowl and a secondary float bowl. Each of the primary venturis feed a rotor,same for secondaries. The primary circuits,jets,air bleeds are smaller than the secondaries and being smaller can easier clog from dirt/rust/debris and not flow as much air/fuel is needed.

What was fuel filter clogged with,plugged up with is a better term for both the filter and carb.. Possible the fuel tank is rusting internally and fuel system is picking up the rust and the fine silt may have gotten thru old filter and made its way into carb causing your symptoms. I notice you don't say anything about the car currently stalling. The idle circuits which move the least amount of fuel thru carb and has the smallest orifices and usually are 1st to show symptoms of low,rough or no idle but you don't mention any of this.

So...things to check in order
-Remove dist cap from distributor and turn over and inspect the terminals(all) for burning/pitting/corrosion. Check that the carbon rotor buttons are present,in good condition. Press down on them lightly and feel for spring tension to hold them against rotor. Look carefully for carbon tracking in dist cap(looks like jagged pencil marks) from/to adjacent terminals . Check rotor contact faces for burning/pitting/corrosion
- Pull all spark plugs and inspect. They are like a window inside the engine and can provide clues by their condition/coloration.
-Pull each coil wire from their respective ignition coil and check for oil on the terminal and or inside the coil tower. The coils are filled with oil to keep them cool in operation and one of signs of impending coil failure is leakage.

-Remove air cleaner and look at the windows on each float bowl(one front/one in back). You should see the fuel level in each window and it should be 1/2 way up the glass for both. This tells you the carburetor is full to correct levels. If they're not approx. 1/2 full that is another clue.You can rock the car to make the fuel jiggle in the bowls to easier see the level. You may have to wipe the bowl windows clean with a rag to see clearly.

Remove fuel filter and inspect. Tap inlet side firmly over a paper towel to see what comes out. Let the towel sit and dry and see what is left. Take a q tip and swab one end in each connecting line to fuel filter and see what comes out. Wipe this on towel also.

If you're not sure of what bad is or how to judge condition of above mentioned parts,take some detailed pics and post them here so we can see what they look like and better guide you to next steps to take.

The other possibility is an igniter failing due to electronic overheat/age. These can cause the car to not show symptoms til it has been running for some time. They will fail intermittently,infrequently in beginning of failure and toward the end will only allow the car to start and run for a shorter and shorter time til it will no longer run.
. You have 2 ignition systems in your car Leading and Trailing. The trailing ignition is there primarily to clean up emissons left over after the leading ignition burn. The trailing ignition provides the trigger for both the dash tach and the fuel pump. Your car will run without trailing ignition til the bowls in carb run dry at which point it will stall and not restart. A good sign trailing ignition is working while your car is experiencing the drivability problem is that the tach is still working at this time. If the leading ignition were to fail the car would run but very poorly with no power and definitely not the way you describe on the carb secondaries. There is a possibility a wiring/connection issue due to age/miles could be causing problem.

It must be determined whether its fuel or ignition by ruling one out and focusing on the other.

tim.

iTrader: (1)

Another possibility is that some debris was blocking part of the idle circuit, and it became dislodged when you loaded the car onto the tow truck and it began to run properly again.
I would take the top off of the carburetor, it is only a half dozen screws, and see if there is dirt in the bottom of the float bowls. Dirt in the fuel system can cause a lot of hell. If you do replace the fuel filter I would cut the old one apart and see what is in there. Don't be afraid to take a look inside the carburetor, just be careful not to drop anything inside the barrels.

ThirdPedalNirvana

Wow, GSLSEforme, that was incredibly thorough!

I will definitely inspect my ignition system. But I really don't think the problem lies there. I should do some exploratory surgery on the carb when I get the chance. The 1 year old fuel filter doesn't appear dirty at all yet. So I think the tank isn't rusting. But the old filter was very brown.

Update: I have driven at least 200 miles since the incident. I mixed some fuel system cleaner into the tank, and I have had no additional problems with this quirky, temperamental, wonderful engine. I have however had an unrelated problem which has now taken priority in my mind, and I am writing a post about that.

Thank you all!

ThirdPedalNirvana

I do consider myself a fairly competent shade tree mechanic. I've done timing belts, valve spring seats, differential & half shaft replacements, as well as the easy stuff (spark plugs oil wheel studs/hubs belts alternator water pump coolant flush radiator brake pads/rotors/lines/bleeding). I seek advice from mechanics time to time but I generally forbid myself from paying someone else to fix my car. I have mentally prepared for rebuilding my rotary engine if it needs it.

The rat's nest intimidates me, because I don't have the option of not passing a smog test, and the carburetor is something that I don't understand as well as fuel injection. Plus, most of the threads I find online say to never take apart a Nikki carb unless you know something is wrong with it. As of right now, it isn't giving me problems, though after reading all the comments in this thread I realize I should be checking it out anyway.

Just wanted to set the record straight that I'm not afraid of a little engine grease . Or, actually, a lot of engine grease. Transmission fluid. Coolant. I dropped the wind-up watch I'm wearing right now in dirty brake fluid. (Amazingly it still works)

DivinDriver

iTrader: (15)

Confirmed, but incomplete as stated; unique to '80 CA/fed electronic ignition, and '79 CA points ignition. Part of the emissions control system.

Trailing ignition is disabled during acceleration from 1100 to 3000 RPM, to keep the mix rich enough to heat the thermal reactor properly, and controlled by both RPM and a vacuum delay switch.

Deceleration control system is based on mixture control (AAB valve, dashpot, richer, etc) , not a disablement of the trailing ignition.

Not an issue on anything 81-forward.

Jeezus

iTrader: (4)

I do not have the wiring diagram handy for an 85, but on the 82 if you swap the yellow w/blue stripe on the leading with the yello w/green stripe wire on the trailing, as well as swap the leading/trailing plug wires, this should let you know if it is an ignition issue. I have ran with no trailing ignition for years and the only downside is increased "emissions" which don't really mean much when you run a full exhaust.

ThirdPedalNirvana

I've now driven through several tanks of fuel, and the issue I experienced has not resurfaced. My best guess is that it was gunk in the fuel system that worked its way out. I appreciate all the input, but I don't have any cause to mess around with a perfectly running engine (well, almost perfect, throttle stabs from idle cause hesitation, but it's easy to ignore). I'll revisit this thread if I have any similar problems again.

tim.

iTrader: (1)

Glad to hear it's running well again.