So, I have a Pro7 Rx7 FB racecar that I bought last year and have been racing up until now. Im having some problems that I hope I can get some insight on from people that are more experienced then me on this.

To start the car has a 12A that made very recently 109HP on the Dyno and is carbureted with 4brl carb. We are having what I think is ignition shut off issues under higher load at higher RPMs. When on the track and giving the car full throttle on straights the car will feel like it hits a rev limiter at about 6k rpm. At that point obviously we lift but if we try to immediately get back on throttle there is nothing there. Almost like the ignition switch is just shut off. I've checked back on the videos and it looks like the car doesn't loose actual ignition power or main power because my electric gauges work during the time. The car will then come down in RPM a little bit and come back alive. We had this happen last time we were at the track and before we went back this weekend we Rebuilt the Carb, Replaced Fuel Filters/Pump, Coils, Plugs, Cap, Rotor and installed a fuel pressure gauge because we thought that was the issue. We went back this weekend to the same problem sadly and are trying to see if anyone here has any ideas. I have a feeling it is the distributor itself or some sensors that fire the coils inside the dist because that seems like it could be "cutting ignition". BTW there is NO ignition box on the car. Just straight coils and dist.

Hope someone can give me some insight.
Thanks ahead,
Sam

 

Not sure what you have going on. I can only relate the weird ignition and fuel stuff that has happened to me while racing.

Ignition:
My car uses an MSD/wasted spark on the leading side and trailing is all OE stuff with an MSD coil. I had a miss similar to yours with this ignition system many years ago. It was the rear rotor ignition wires arching on the steering box. The wires set I had was a little old and I didn't have the wires secured very well. I replaced the wires and added insulation to both the leading and the trailing wires. Also use wire ties to keep them from flopping around.

The screws that hold the "breaker plate" in the distributor came out and every thing was flopping around. I had some other issues with wiring in the distributor but the missing screws didn't help. From now on I look at everything.

Over the years I have had arching in the distributor cap. It sounds like you replaced that along with the rotor, You might want to look at the old cap and rotor to see if there is any indications that the rotor was hitting the cap. That might indicate bad distributor bearings. I only use OE Mazda Cap and Rotor sets for what it is worth.

If never had an OE ignition igniter fail on my car, So, I am not familiar with symptoms when they go bad, I always assumed they are like all other OE ignition modules in that when they go bad the stop working completely. If you do decide to replace them, I would do the Leading igniter first.

Fuel System:
I use two carter fuel pumps on my car. I have had one of the two pumps go bad at a race. The good pump would push fuel past the bad pump and starve the engine at high RPMs. Now I replace the pumps often and I installed one way check values so they can't push fuel past each other.

I have had issues with fuel cell/fuel tank vents in the past. If the cell or tank isn't vented properly eventually the pump(s) will stop moving fuel to the carb. When that happens, the car will shut down until it vents. I have a 3/8" fuel hose with an inline filter on my cell vent. I make sure that the end of the filter not obstructed.

It hasn't happened to me, but fuel cell foam goes bad and can clog up filters. Even brand new ones that were just installed. I check the foam in my cell every year and replace it before it gets bad.

 

Float level more than likely - I'd also swap over to an IDA if I were you.

 

What was the fuel pressure gauge showing when this happened?

Does your 12A have a header or stock exhaust manifold? 109HP is kind of low, unless you are running fully stock carb and stock exhaust manifold. The Pro7's typically made 115-118HP with some modifications to the carb jetting to richen things up. With a Racing Beat header you can easily get 135HP with stock carb and jetting modifications. That is all in stock port 12A.

Carl

 

First off, sounds like an ignition issue for sure. I would check the integrity of the dizzy since you already replaced a bunch of other parts. When ignitors fail they generally work well until they get hot then start to break up the ignition and as they fail that become worse over time until it just stops working all together.

It could be fuel related even if the pressure is good, the flow might not be good enough. Not sure what fuel pump you are running.

Yeah that HP is at the wheels I assume. I have a stock port 12A and at one point it got 134HP to the wheels on a dyno. Not sure what they allow in the class you run though.

 

From a fuel pressure point of view, I was thinking of maybe starvation. Kind of like I used to experience on lower fuel load going through the final few corners before the front straight at Auto Club Speedway. The bowls wouldn't go empty until about the start/finish line when the engine would have similar reaction to described above. It would come back a few moments later (and of course at that point, the revs would be down). Probably not this, but worth considering and rejecting.

If the fuel pump is working, even the stock pump can easily handle 109HP. We raced Spec7 with the stock pump. Pretty sure there was no other option allowed.

I agree that ignition also is a decent possibility.

Carl

 

That sounds like textbook fuel starvation. The pickup in the fuel tank may be plugged, so even if you have a new pump and filter, you may not be getting enough volume.

You can also check for a fuel leak in the hoses/lines running over the axle from the tank to the pump. They won't leak out but they can draw air in.

If the rules allow, cap off the return line. If the rules don't allow, place a big ol' ball bearing in the return hose

I'd also go colder on the plugs, heat range 9s all around.

 

i third this diagnosis. not enough volume, that's what it sounds like to me.

 

i like to run a volume test, the procedure is in the manuals.

but you need some kind of container that has volume markings on it, it needs to be at least a liter. and a stopwatch.
the one i have was supposed to be for juice, and it had marks every 100cc.

take the fuel line off the carb, and put it in your container. turn key on, and start stopwatch, and see how much you get
if your container is 1 liter, then you run it for 30 seconds. i run the 30 second test a couple/few times to get a good number
if its bigger, you can do 1 minute.

put the gas back in the tank when you're done.

i believe the spec for the stock pump is 1400cc/minute? (its in the manual)

 

I'm going to dissent from the fuel comments above and suggest you check Ignitors, and then coils. What you describe about high RPM failure could be the leading ignition dropping out, and the engine only running on trailing. When this occurs, you'll lose a ton of power. The Leading Ignitor is located on the front of he distributor, while Trailing Ignitor faces the Alternator. It's easier and faster to uninstall the Alternator and move it aside to remove the Trailing Ignitor. There should be computer chip thermal paste on the back of the Ignitor where it contacts the Distributor - this functions as a heat sink, otherwise the Ignitor will overheat. When it does, it will fail intermittently, and your coil won't fire consistently, or at all.

If your Ignitors both check out okay using the FSM and a test bulb, then start looking at the Coils. The original Mitsubishi diamond coils were the best, and aftermarket Coils must be the type that allow for horizontal mounting. If not, they'll leak mineral oil and get intermittent until they stop working entirely. We had a user here who had a problem with ignition cutout in hard right turns, and he found that his Leading Coil was running dry and the mineral oil was sloshing to the base of the coil, killing spark. My bet is that it's one of the two things above,