Idle drops in stop-go traffic

[mosu]

My normal 900 rpm idle sits nice and steady after a long highway cruise or generally moving traffic. However, if I'm stuck in gridlock and idle for longer periods of time it starts dropping and vibrating badly. If i rev the motor on the spot, it has an intermittent miss.

Are my plugs getting fouled from idling? This doesn't seem normal, even for a points ignition car...

[skumandeth]

Sounds like it's possible your idle mixture could be on the rich side, and it is fouling a little. First thing I'd check.

[mosu]

It *sounds* like it's at the smoothest point of the mixture screw...idle jet is 45 so I don't think that's out of spec for a DMSA. What could be causing additional fuel to be pulled out of the carb? Float is adjusted properly and not sinking.

[So Cal Mark]

with the engine idling and the air cleaner lid off, look down the carb throat. If you see fuel dripping from the main discharge nozzle you either have a high float level, high idle speed or improper throttle angle opening.

[mosu]

Aha, that helps...fuel isn't just dripping, it's got a steady pour down the main discharge nozzle. I was a bit puzzled cause I thought the idle jet was under the throttle plate...

The throttle stop screw is barely contacting the lever thing, maybe 1/2 turn in at the max. Float is adjusted and double checked to spec, and I even swapped floats with a known good part. I guess that leaves improper angle opening...Mark, how can I bring that back into spec? What is the spec anyhow, I didn't know it was adjustable...can it be done with the carb on the car?

[So Cal Mark]

well, since your idle stop screw is backed out you'll have to check a couple of other things. First, disconnect the linkage and see if the throttle will close any further. If not, you need to remove the carb, turn it upside down and see if the throttle plate is misaligned in the bore. Carb kits used to come with new throttle plates, so it's possible someone replaced them and didn't get them aligned properly. It's rare but possible. Hopefully it's just misadjusted linkage

[majicwrench]

Make sure chaoke fast idle cam isn't holding throttle up. Also, often when the idle circuit becomes plugged, people turn up the idle screw enough that it starts sucking fuel thru main system discharge nozzle. If it's been that way a long time you may have to very gently push throttle lever to get plates to close once idle stop screw is backed off.
Usually is something simple holding throttle plates open. Good luck.
Keith

[mosu]

Cheers guys, thanks for the pointers! I must say that this DMS is turning into more trouble than it's worth. So far its only redeeming quality is the amazing sound it makes on a short rip with no air filter

The car's in my dad's garage so I'll ask ahead of time to know what to do:

If the linkage is holding the throttle slightly open, can it be adjusted? If I recall, mine is the solid kind, with no cables.

In the bad news case, if I have to remove the carb, what's an easy way to do it? The first (and I hoped last time), I had to take off the accel pump, linkage rods, and still twisting a wrench in there was a millimetric affair. What's a good way of removing it?