RX-7 Stumbles

So, I got the exhaust on and had rebuilt the carb 2 plus times. With the correct needles and seats, it ran amazingly well! Go figure. Drove it to work one day and it did pretty good. Maybe needed a little tweak to the carb, but ran without issues, there and back home.

Totally the same

A couple days later, I decide it’s time to register it in Utah after a decade. I really liked the Ohio historic plate (and the fact that it didn’t need to be registered every year) but now it would qualify for the Utah vintage registration. Plus the “new” historic plate in Utah is all black with white letters and not the silly Model T design. And it was a bit over the “all vehicles must be registered within 60 days of moving your permanent residence to Utah”. Whatever.

I put it on stands and checked all the exhaust bolts after a few heat cycles. Mostly nice and tight with just a couple needing to be retorqued. Drop it back on the ground and time to head to the DMV.

But…while it idles good, any throttle causes a stumble. This isn’t totally unexpected as the fuel mixture screw got completely out of adjustment when rebuilding the carb and the manual instructions are basically “use an exhaust gas analyzer.” Thanks…dicks.

So, I scoure the internet for any hints of a car that is 40 years old, hoping for an answer on a forum that hasn’t seen a post in 10 years. It does not go well.

I finally find something buried deep on page 3 on an old thread on the 4th website. “IIRC, turn it all the way in, and then back it out 3 to 4 turns. I’d start at 3.5.” I should mention that my old Hayes manual shows a carb that is similar, but not totally accurate to the one on my car. It does mention that you should turn the mixture in until it hunts. Then back it off until it runs stable, and then add another 1/4 turn. This is a plan.

Turn mixture screw in, then back out 3 and a half turns. Fire up the car. Turn in until it hunts,  then back it off. And back it off. And back it off. Finally runs smooth-ish, but now the idle speed is high. Any throttle causes a pop in the exhaust. ?? Does that mean it’s too lean or too rich. Turn off car and back to the internet.

“Backfires indicate an incorrectly adjusted fuel mixture. This could be caused by the mixture being too rich or too lean. Use an exhaust gas analyzer to…”

Oh, for fuck’s sake!

After fiddling with it for an hour, I’ve got it idling fairly well and only popping slightly under certain throttle conditions. Fuck it. Off to the DMV.

The first stretch of 65mph road is going fairly well. A little stumble from the stop sign, but seems to run ok. Then I get into town at the first stop light….where it stumbles and dies. Shit. Hit the key as the light turns green and luckily it fires and I crawl through the intersection with the engine stumbling hard.  Pull over and pop the hood. Thinking it might be too rich, I lean out the mixture.

Down the road a half mile and it’s definitely worse. Pull over again and crank it back. The next bit of driving is through traffic and lights. I discover that if I keep the idle speed up around 3k, it doesn’t stumble off the line. Sweet. Make some noise.  At least it makes it across town to the DMV.

Go inside. “Do you have an appointment?” Shit, that’s right. They just started doing this bullshit. “No.” “OK, it’s currently an hour and a half wait, unless others with appointments show up, and then you’ll be bumped down the list.”

Grab a seat at look at the Now Serving board: 7 no appointments and 1 with. Of course, I’m last at 1.5 hours. After 30 minutes, I notice that I’m now listed as 2+ hours and there are 6 no appointments and 6 with. Oh fuck this shit. I get on my phone and make an appointment for the next morning. As I stand up, my time shows 2.5+ hours. Bye bitches.

The ride home was about the same as the rise there, except now the engine prefers being at 3.5k at idle to prevent stumbling away from a light. Cool, cool.

At home, I check the timing, as some rando who stopped by during one of my hood up moments suggested. It was dead on. I check the plugs and they are old and need cleaning. Seems like it is rich. I lean out the mixture, but that seems to create more back firing on throttle. Go back halfway and call it a night.

The next morning I get to the garage 30 mins before I should leave. Fire it up. It seems somewhat happy with the choke on, but any throttle causes more popping. Nothing I do makes a difference. Unhappily, I take off for the DMV, take 2.

It’s definitely worse than yesterday. Back-firing is very common and it just doesn’t feel balanced. It is almost as if the plugs get fouled and only high revs help. It makes it there.

DMV2, The Return, went much smoother. Check in, and as my ass hits the seat, they call me up. Takes 5 minutes and she walks me out to do a VIN inspection and let’s me go with my temp tag. One thing I noticed while sitting there the previous day is that they only staff for appointments. As soon as a clerk is done, they vanish until someone with an appointment shows up and then they magically appear at their desk and call them up. Lousy way to run an office.

Happy to have the paperwork out of the way, I fire up the angry engine and limp towards home. I actually try an adjustment in the DMV parking lot. It was so bad, I pulled over to the side of a 60mph road to put it back. I’m starting to think it might be a fuel filter. I know I had bad fuel that gunked up the carb, so I think it makes sense.

But it’s running so bad, rather than stop by the parts store, I take the long, quiet road home so I won’t be a traffic clog. And it’s a good thing, I check online back home and they didn’t have either the fuel filter or the spark plugs in stock. I’m sure they have a filter that would fit, but I need to figure out the hose size before grabbing the wrong one.

At least the car is now registered. Just not driveable.

A week later, I find some plugs and a filter that will work that are “in stock” at a parts place about 25 mins away. It’s in Hilldale…the known polygamist FLDS stronghold. To fit in, I drive Ike and wear my greasy garage clothes.

Now Ike, he fires right up, but joins the stumble club. However, this is not a new issue. I usually just jiggle with wires on the #5 cylinder and it smoothes out. I clear out the engine code and set off. I had to stop to drop off the glass at the recycle center, and upon restart, same stumble. Try the wire wiggling trick on #5, but no change. I check the engine code (bluetooth to my phone) and now it is showing misfire on #4 and #6. At least #5 is working! Wiggle more wires and rev it up and it seems ok. Ish.

Fuck it. Up the hill I go. Even running on 5 cylinders randomly, Ike pulls up the big hill easily. About halfway out to Hilldale, I get slowed to 55mph behind traffic. Stupid tourists who can’t read a speed target, er limit, sign. At 55mph, Ike starts to make a noise. It only sounds like the impending doom of a motor mount, but if I add some throttle, it down-shifts and the rattle is gone. Fixed!

Get to the parts store and sure enough, they don’t have the stock. They have 1 spark plug, not the 4 shown online. 1 plug does me no good. At least I picked up a fuel filter. But, there is a sliver lining to this trip. One of our favorite restaurants from Springdale lost their lease a year ago and relocated to this hick town. So I go over and notice that Ike’s knocking rattle is getting worse, even at idle now. I ignore it and go in for a chimichanga. The owner and servers chat with me so much that my food gets cold. I don’t care. It’s also technically my 2nd lunch anyway. Unfortunately, their liquor license is still pending, so no margaritas. Spend about 2 hours eating and visiting.

Driving home, Ike’s loud knocking is mysteriously missing. Maybe whatever it was fell off? Whatever. Not an issue anymore.

Get home and throw on the fuel filter. Seeing as how easily the fuel falls out of the filter, all down my arm, past the elbow, I guess the filter isn’t the problem. I can blow through it without issue. Wait 10 minutes for the fumes to run and hide, then fire it up. Yup, fuel filter wasn’t it. It is still angry. Sometimes I hate being right. Just kidding.

Jump online and order plugs from Rockauto. What the hell, I order new coils as well. Maybe there isn’t enough spark. They show up a few days later. I get an email that they were delivered to my PO Box. Sweet.

I drive the 10 minutes down the hill, BECAUSE OUR GOVERNMENT IS TOO FUCKING CHEAP TO RENEW OUR TOWN POST OFFICE LEASE! Thanks for the fucking DeJoy, you asshole. Open the PO Box and there is a slip of paper. Oh fuck no. This means that instead of putting my “oversized” box into one of the overflow parcel boxes and leaving me a key, they make me show up the next day to get it from the teller. Well shit.

After driving back home in a fit of rage (there might have been 2 racer-style passes), I head out to the garage to install the new coils I got. While that goes easy, I notice that one of the two coils has been unboxed already. Sure enough, there is a dent on the bottom where someone dropped and returned it. I’ll use it for the trailing ignition because I can only imagine the nightmare of trying to sort that mess out.


While I’m waiting ever so patiently for my plugs, I decide to make an improvement. I should probably mention that besides replacing the exhaust, I also removed the “rats nest” from the engine. Basically, any silly thing meant for 80s emissions gets yoinked off the carb and the top of the engine. There is a lot. Most of it vacuum tubes and solenoids. But there are two places where you need to make blockoff plates.

Just part of the rats nest

I had used what I had, which was thin gage sheet steel. Something I could cut with snips. I used two layers for rigidity, but I wasn’t really happy with them. Since then, I had found a piece of 1/8″ aluminum and I have this welder/plasma cutter I’ve never used….

Rats nest be gone!

I mark out the outline on the new plate and prep the plasma cutter. How many tines have I done this? None. How hard could it be? Well, not as easy as it looks. A few test cuts just proves my notice status, but then I say fuck it and hack out the pieces.  Then get to work with the grinder. And the file. Drill some holes and I’m done. And they good? Good enough.

I clean them up, slather with Ultra Copper sealant and snug them up. An hour layer, I torque them down. Much more solid than the last pieces, and possibly the fix for the whole issue. On the larger of the two plates, there was one 1/8″ spot that looked oily (fuel residue?) under the permatex. If that was letting in air, that would cause the backfiring. Gotta wait 24 hours for the sealant to cure before it test it though.

Next morning, go down to post office, pick up the parts and manage not to hit the guy over the head with it. Install the new plugs (the old ones are VERY old and VERY used looking. Torque them up, install wires back and check the watch. It’s about 21 hours in. Surely the permatex is set enough. Right???

Fuck it. Reset the fuel mixture to 3.5 turns. Fire it up. Wait for choke to release and lower the idle speed. Well, it’s running. Turn mixture lean until it hunts, go back rich until smooth, then add 1/4 turn. It definitely sounds better at idle. Blip the throttle. No backfiring. No dogs barking at back fire. (My neighbors love me.) Jump in and drive around the block. Seems to be working! Cautiously optimistic.

So much so, I decide to drive it to work. Sure, I put a bunch of tools into the passenger floor….details. I’m totally (maybe half) confident.

Get ready for work and head off. It was an uneventful drive. Smooth and good sounding. About time.

I still don’t know if it was the coils, the plugs or the block off plates, but something there fixed it.

At least, until the drive home tonight…fingers crossed!

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