Ever since Ukraine both the Fiesta and the Marbella have been idling roughly. To the point where we can’t keeps them running when stopped without feathering the throttle or pulling the choke (real nuissance in traffic). We’ve got a few ideas on what may be wrong, but are looking for a little help. Any knowledgable carburetor-heads out there?

We’ve seen vague posts by other teams with similar symptoms and read that they’ve had to adjust their timing to solve the problem. Not sure if this is the way to go or how to do it.

Our best guess so far is that the quality of gasoline has been steadily declining the farther east we drive. So we’re thinking maybe a clogged fuel filter (Note: we’ve been dusting off the air filters for quite some time). Next step here is to figure out how to get at it.

Slow idle on the Seat is already as high as it will go. Not sure about the Fiesta. Distributor contacts on the Seat are heavily pitted. Doubt we’ll be finding a spare around here any time soon.

Fiesta had new plugs when we set off, but we’ll probably take a look at them when we get a chance.

Any thoughts, questions, whatever are certainly welcome.

dominic

2 Responses to “carbo posting”

1. Nick Says:
   August 8th, 2006 at 8:56 am

   Rough idling, hmmm? I’m no carb-head, but I love trying to find answers on the interweb. Since someone else may weigh in who actually know’s something, I’ll try and share moderatly entertaining pieces of what I find:
   *goes and gleefully googles*
   ok, so it could be a zillion different things…
   like “Try having the SPI Injector cleaned ultrasonically. It can make a world of difference”
   So go ahead and give that a shot guys. In all seriousness, the more info on your symptoms that you can throw at us, the more likely you can get a diagnosis that would be worthwhile. Until then, here’s some car talk, rough idling and or low rpm stalling-related answers:
   ************
   Tom: But you should be able to figure out what’s wrong with it. The first thing I would look for is a sticking exhaust gas recirculation (EGR) valve. The EGR valve, as the name implies, recirculates exhaust gas back into the combustion chambers during acceleration. If it’s not closing when it’s supposed to, it could be letting exhaust gas contaminate the mixture during other times, which could cause rough idling and stalling–particularly when the engine is turning slowly.
   ************
   Ray: The other possibility is that he has no idea what he’s doing, or isn’t particularly interested in solving your problem. Before I sent you to a dealer to pay for a digital readout, there are a couple of simple things I’d do. First, I’d fix that vacuum leak he mentions. That could cause excessive fuel consumption and rough idling.

   Tom: But even before that, I’d do a compression test to see if the engine is basically sound. At 154,000 miles, one of the valves could easily be burned. And that certainly would cause rough idling.
   ************
   Ray: So assuming your compression is OK, my guess is that you have a ruptured auxiliary accelerator pump (AAP) diaphragm.

   Tom: When that diaphragm breaks, excess gasoline pours into the No.1 cylinder and gas fouls that spark plug, causing that cylinder to not fire.

   Ray: If your dad or your boyfriend are mechanically inclined, ask one of them to remove the No.1 plug and see if it’s all wet with gasoline. If it is, the AAP diaphragm is what you need.

   Tom: If the plugs are clean, you may have an intake manifold leak. A bad manifold gasket would allow too much air to get into one of the cylinders. And if there’s too much air in there — just like if there’s too much gas — the cylinder won’t fire.
   ***********

   Here are some questions which relate to items that could be the source of the rough idling:
   Does it sound like all the cylinders are firing? Have you noticed a drop in power? (yeah, if it were the plugs, you’d be on them in a second I’m sure)

   Was this the car that had the head gasket issue?
   if so a leak or rupture could wreak some idling havoc.

   (from car talk’s website on rough idling issues)

2. Sam Says:
   August 8th, 2006 at 9:14 am

   BCMC:
   I love watching your progress; It’s become ritual every morning.
   Onto your carbs
   Since you aren’t experiencing problems at speed and you are able to keep the cars running “choked”, try removing the idle speed screw/needle valve/jet which is just below the throttle plate. If you find nothing there check the idle air bleed passage above the throttle plate for restrictions. I’m guessing that if you move the throttle just off idle, the cars can maintain constant speed?

   There may also be a idle cut off solenoid on the carbs to transition between idle and part throttle, maybe this isn’t working in the idle mode. Check for power and ground if you have this.

   Other things…if idle speed is set too high you may be leaning out the mixture. Maybe try backing it down a bit to see if it helps?

   As fuel quality degrades you may need to retard timing like you say but I would think this would affect you throughout the engine speed range. You should hear pinging from pre detonation and decreased power…relatively. I’ll try to research how to retard the timing in the fiesta today. Try the above recommendations in the meantime.

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