ThirdPedalNirvana

Well, it had to happen eventually, it might as well have been last night . I had to call AAA and get a tow to my house when a brief outing in my 1985 RX-7 GSL went sour. I appreciate your patience with me as all my previous cars have had computers to tell me whats wrong and fuel injectors. I am new to (1) owning a car older than me, (2) owning a rotary, and (3) owning a carburetor.

The earliest indications of trouble, which I wrote about perviously on this forum, was a tendency for the car to overheat (or at least get hotter than it should) when climbing hills. I have a prestone kit and was planning to flush all the coolant soon, also I bought a new thermostat because it's $20 and might as well go in when the coolant is being drained. My dad had asked if the car was running lean, which could cause it to overheat under load, but I thought it couldn't be, because it passed a smog test when I bought it just over 2 months ago, and running lean would cause it to fail, right? (Yes, this is a CA car with the stock carburetor and emissions system)

Also the computer adjusts the AFR based on the O2 sensor, right?


The car drove fine otherwise, until yesterday.

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The first problem I noticed was stepping on the throttle from idle caused a stumble before the revs climbed. I thought maybe accelerator pump, but it didn't seem to be affecting driveability otherwise.

The second problem I slightly noticed was some occasional barely-felt hesitations while cruising at around 2500 rpm. Knowing I need new shocks and possibly wheel bearings, I at first assumed I was just being paranoid, as I could get consistent acceleration with a downshift.

Then I came to a stop and the idle was really low . I-can't-believe-its-not-stalling low. I think the tach on an '85 FB has the first tick at 500 rpm, the idle was just a hair below that. I had to give it gas for a half second before starting to let up on the clutch or it would stall. At this point, once I was moving the car felt fine.

After arriving at my destination, a drive-thru, I had to stop in the middle of my order because of the aforementioned low idle, the temp was higher than I wanted, and I smelled smoke . Turned out to just be old spilled oil coming off the block, nothing significant from the exhaust, so I went into the restaurant instead and ate dinner while letting the car cool off.

When I left, the car started right up, I put it in reverse, backed it out of the space, and it stalled.

I started the car up, drove forward 15 feet, and it stalled.

I bump-started the car (as I was still rolling), drove another 20 feet, and it stalled.

I want to clarify: the car was not stalling when I was off the gas. I was on the gas, trying to accelerate, after a second or 2 of acceleration, the engine would just die. More throttle made that moment come sooner. Once I was convinced that a heavier right foot wouldn't get me home, and becoming increasingly concerned about trying to drive a 32 year old car that was acting up, I elected to park by the adjacent starbucks and wait the requisite hour and 15 minutes for a flatbed AAA truck.

The truck driver was able to get the car onto the truck without the winch, stalling once after backing the car out of the parking space, but making it all the way up the ramp (10 seconds of running or so). When we got back to my property, the car was backed off the truck under its own power. It stalled again, but then I was able to drive it up my inclined driveway to it's usual parking space. On the incline, it idled, though still very low.

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The old adage is fuel, spark, air.... I have no reason to think its a spark or timing problem, and there's nothing blocking the air, which leaves fuel. All the symptoms seem consistent (to me) with an inconsistent fuel supply. My question is: where do I start?

Could it be an adjustment on the carburetor that got off? I know several adjustments are handled by the computer via vacuum actuated devices, and if those are malfunctioning, there is supposed to be a warning on the dash from the primitive emissions control unit. I'm fairly certain idle speed is a manual adjustment, but that shouldn't cause the engine to fuel starve when it's not idling. The concurrence of these failures makes me think its traceable to one problem, and occam's razor suggests its a lack of fuel in the carburetor. (float bowl adjustment??)

With no input from this forum I would probably start with a new fuel filter and hope for the best. If anyone knows a guide for diagnosing fuel delivery problems, or checking the fuel lines for blockages, I'm all ears.

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I know my car needs plenty of freshening up, but despite that and having 2 other cars I could be driving, I still found myself trying to take it on some kind of outing every couple of days. It's addictive, and I'm going to miss it while it's out for the count.

Thanks in advance for the help!

ThirdPedalNirvana

Thankfully it wasn't a misadjusted carb that was causing my drivability issues. It was just the fuel filter.

Here's the old filter held up to the newly installed filter:



I'm going to keep a close eye on the filter, because if the tank is dirty or rusting I'll expect to see a lot of buildup in the new, clean filter fairly soon.


Kaylee is driving nicely now, courtesy of the fuel filter and an oil change/oil filter. The temperature control problems climbing hills wasn't solved by this, suggesting that the car's not overheating due to a lean fuel condition, but likely sludge in the coolant system I need to flush out (and possibly new radiator).



If anyone is looking for a guide to how to replace your fuel filter... I'm guessing you haven't jacked up the rear end of your car before because it is fairly obvious, but reading about it can help. I'll write up what I did. The filter isn't hard to find, over by the driver's side rear wheel well. Here's the tools you'll need:

-Floor Jack
-Jack Stands
-Pliers
-Bucket or Tray
-One Friend/Extra set of hands (optional)

Make sure the car is parked on a flat surface. Jack up the rear end of the car by placing the floor jack under the differential. Place the jack stands under the frame rails where they are visibly reinforced, and lower the car onto the jack stands. Remove the floor jack so you have room to work.

As always, do the hump test (slam your body into the car from a few different angles) to make sure the car is stable resting on the jack stands. If the car shifts or moves in any way when you do that, do not climb under the car. Readjust the jack stands until the car is resting in a stable way.

There is a simple wire clip holding the fuel filter in place. The fuel lines are flexible. Unclip the fuel filter from the body of the car.

Use the pliers to move the spring-type hose clamps a good 4 inches or so down the fuel line, away from the filter.

Place the tray or bucket under the fuel filter. Fuel will spill out as you replace the filter.

Disconnect the fuel line going from the tank to the filter. Note: in a carbureted RX-7, the fuel filter is gravity-fed. That means gas is going to keep coming out of that fuel line you just disconnected until the tank is nearly empty. I did not know this, and I wasted about a quart and a half of fuel waiting for the flow down the fuel line to stop before I realized it wasn't going to stop until the tank was empty.

Your options are: (A) do the fuel filter swap quickly and catch all the gas that pours out in your bucket or tray, or (B) enlist the temporary help of a friend to pinch closed the fuel line with the pliers while you're removing the old filter and installing the new one. Using the pliers to clamp the fuel hose wont stop the flow completely, but it will reduce it to a small trickle (or rather, if you do stop the flow completely, you might be squeezing the pliers hard enough to damage the fuel line. So don't do that).

Disconnect the fuel line going from the fuel filter to the front of the car. You've now removed your old fuel filter.

Install the new filter by checking the flow direction arrow on the filter itself. Insert the plastic tube on the fuel outlet (arrow points towards it) into the line running to the front of the car, and attach the other plastic tube (the fuel inlet) into the line running to the gas tank. Your friend can now release the pliers they are using to stem the fuel flow. Once they do, you'll notice the bottom of the fuel filter filling with gas.

Use the pliers to move the spring-type hose clamps back towards the filter, keeping the fuel lines attached securely.

Clip the fuel filter into the wire clips that hold it in place.

And that's it!