racermike

"""raining""" ?? I thought we sent you snow?

85RX7GS

iTrader: (1)

NJ is supposed to get snow on Freitag.

82transam

iTrader: (18)

ok, here's something I forgot to say before, it might narrow things down, I don't know. Anyway, If I go into town on an average winter morning (~30 degreeF) the choke will pull in right before I get the parking lot of the local strip mall. Of course it stall so I have to either hold the choke out or just let it stall and pull into a parking spot. Get out of the car, go rent a video, go to the bank whatever I'm there for, come back out to the car, turn the key and it will start right up, and idle fine. Its always done this I guess I forgot to mention it. WTF is up with that? Its just sitting there turned off, how can that make it magically idle? any thoughts?

racermike

hummm, Well the choke should disengage at a pre-determined temp. If it is behaving properly and the car still stalls (no other problem or causes), maybe the air / carb, is too cold. After you let it set a few minutes, the "heat" will migrate around and possibly faster than when the car is in motion. The water that is circulated in the intake is too warm the carb so that it doesn't ice up in the cold. Depending on the year, there is also an exhaust feed (emissions??) to the intake. All carbed motors with a stock air cleaner (I believe) have a trap door in the "snout". It directs pre-heated air from around the exhaust into the filter until the temp. causes it to "open" to the "snout" intake. Do you have the flexible pre-heat tube installed? Is the "flap" in the air cleaner operating properly??

82transam

iTrader: (18)

Hmmm, I guess that makes sense, since the fan isn't moving air around the heat could build up more. As for that hot air hose thing, I ripped all that off a few weeks ago, it obvioulsy didn't help since my car has done this for over a year. I still haven't gotton a chance to replace that temp sensor on the water pump, I'll try that before doing anything else.

Huskyfox

It's funny (well not really) but my car (Stock 81 GSL) has been doing this exact same thing, for over a year now. Mine used to be identical to that, but it has become progressively worse. It still idles smooth and fine when I first start it, even on the coldest days (so long as I pull the choke out only enough to idle it around 1000Rpm) but if it is a cold day (less than 40F), as it warms and nears normal operating temp it starts to slow down, more and more till it just dies. I can get some more time by pulling the choke out further (which for a moment before getting up around 1500rpm will actually make it want to stall a bit more, same thing happens if I give it just a little throttle, that will sometimes kill it) But as I said it has become worse over time, unless I am to sit there holding it above 1800rpm it will stall.. even if I give it enough throttle to stay at about 1200 and hold it there it will slowly go down on it's own till it dies. I have driven it like that before up to 20mi, it drives just great, but even between gears I can see the RPM's fall very fast if it gets under 2000... When I must come to a stop it will stall, but restarts just fine, sometimes will suddenly idle fine, sometimes I must hold the choke or the keep the throttle down a bit till the signal goes green.. Like 82transam’s car if I let it stall a few times that seems to actually speed up getting it to idle as it should.. and also the same deal for sitting, if I just let it be for awhile once it’s warm and come back to it, it will usually idle fine. When all is well it idles right at 850rpm, smooth as can be. My plugs, wires, cap, rotor, all new.. Timing checked twice. Only thing I have found from playing around while it does this is that turning the idle-mixture till it is tightly shut actually smooths it out and keeps it from stalling... so it seems it wants less fuel during this period.. of course it will not run at all if I keep it that way after it becomes 'normal' I have tried playing with the idle mixture and speed MANY times during it, and nothing helped. I'm geting a rebuilt carburetor soon in hope of a fix.

Aviator 902S

That is precisely what I was going to suggest. Without that pre-heat tube running from the exhaust manifold to the "snout" of the stock air cleaner housing the car will run like crap until completely warmed up. I just replaced the one in my '85 GSL 12A ($13) and it fixed the problem. The old one had torn at the base and the inner liner had caved in on itself, causing cold air to be ingested rather than warm air.


When the choke is pulled and the pre-heat tube is missing or broken, the car runs rich and idles high, albiet rougher than normal. Once the engine temp gets almost to peak value and the choke retracts the mixure is much leaner. Idle rpm should drop to it's normal 750 or so where it should stay. But instead it drops much faster than normal right through 750 rpm to zero rpm. The problem is even worse when it's also damp outside. But after a few more minutes the temp reaches normal and the car idles fine. WTF is going on?

My theory goes something like this:

When ambient temps are below freezing, air is much more dense than normal. This means there is more air by weight than normal, but the weight of incoming fuel remains the same.

This means that the air/fuel mix is even leaner than normal. Too lean in fact. Sure, once the engine is established at idle it stays there. Try it--- instead of letting off the gas abruptly, ease it off and let the revs drop to idle slowly until at idle. Even just after the choke retracts and before max temp is reached it should not stall. This is because the engine is now running rich again at idle due to the idle system which allows fuel to enter downstream of the throttle plate.

Because the pre-heat tube is missing and the engine isn't completely warmed up, the incoming air is not warm enough. Only when the engine reaches full operating temp is there enough warmth in the engine bay to provide the proper incoming air density and the proper air/fuel ratio.

With the choke still pulled, the richer mix is still too rich to allow the engine to reach operating temp. Once it retracts the leaner mixture allows the engine to warm all the way up, but in the few minutes that it takes for this to occur you will have a stalling problem.

Moisture in the air exacerbates this because it cools the incoming air, making it even more dense. (This is the basic principle of water injection systems btw).

With a pre-heat tube in good condition the air pulled into the carb is preheated by the exhaust manifold, even after only a few minutes of operation. By the time the choke retracts the incoming air is sufficiently warm to not only eliminate air/ fuel ratio problems but also to modulate the thermostatic flap in the snout so that the incoming air doesn't become TOO warm.

I hope this makes sense to somebody besides me because I'm out of ideas...

Huskyfox

This sounds good, though for myself I still had this problem even back when I had my stock exhaust manifold along with the hot air tube for the air cleaner all installed.

Aviator 902S

Was the thremostatic flap in the "snout" of the air filter housing operating properly? If stuck in the open position you'd still have had cold air bypassing the pre-heat duct.

It looks like one of those snags that need to be rooted out by changing one thing at a time. In your case, the first thing to do would be to re-install the stock set-up or fabricate a shroud that fits over the header in the same manner as the stock one did over the factory exhaust manifold. Otherwise it will run like crap on cold days no matter what you do.

If this doesn't solve the problem the next thing is to confirm the way in which the car stalls. If it runs fine at idle but then "loads up", ie: the revs slowly drop until the engine quits, you are running too rich. You said yours does this on cold days with the choke pulled. If you shut the car down while it is doing this and pull one of the leading plugs you may find that it is dry but sooty. This confirms what is happening. Where do you have your idle mixture set at? If it's turned out too far (counter-clockwise= richer) you might want to try turning it in 1/2 turn at a time to see if that helps.

If the car runs fine at cruise rpm but quits immediately when you let off the gas it's something else. My above theory wouldn't be the fix if all is well with your pre-heat set-up, but what about your ignitors? Unscrew them from the side of the distributor, disconnect the electrical couplings and inspect the contacts. Are they corroded? When I cleaned mine it made a big difference--- on warmer days. The problem didn't go away on cold days until I replaced the pre-heat duct. I also have less than 5000 miles on my distributor cap and rotor, plugs and wires are less than a year old (NGK), and I have a strong battery.

cdrad51

FWIW, I have a Sterling carb, which has no choke. I have a RB air filter box, so no pre-heat tube. I also have DLIDFIS and Baster 2 coils for leading ignition. Early in the morning, when the car is started for the first time, I fire it up, take it to 2000 rpm, and after about 20-30 seconds I can go down to idle speed and the car will idle perfectly. Or I can keep it at 2k rpm for a faster warm-up. At any other point in the day, even if the car temp is all the way down, I can just fire it up with a quick turn of the key, and it will idle right away.

Huskyfox

...Yes the flap works, infact in this weather it's usually closed from taking in cold air in the front. That was so even with the stock exhaust manifold and air tube installed untill it was VERY warm. There is no way i'm going to take my header off and buy a new pre-cat so I can use the stock exhaust again when I already know and said that this issue was in effect back when I still had all of the stock exhaust components in place. I've been talking it over with a couple people who know and rebuild carbs, I have been told that the car can run perfectly fine without the flap or the hot air hose installed, and any change would certainly not be adverse enough to cause something like this. Also that my issue is almost certainly a leak of some sort.

I'm having my carb rebuilt and will post back the results after to let you all know if it solved the problem.

Aviator 902S

You're in California so it's not likely that you ever see temps below freezing. Our cars warm up and run ok too until the temps take a dive, then the headaches begin.

Aviator 902S

Changing the pre-heat duct did solve my problem in cold weather but who knows? If there's a way to get around this I'm all ears. Do keep us posted.

cdrad51

That's true. Low 30s is the lowest I've seen recently, and that's not common.

RoyFifo

It could be carb Ice. you might try adding a quart or so of Denatured alcohol to your tank and see if that fixes the problem.

Aviator 902S

Now that IS a possibility, although I've never seen it on these cars. Then again It's the kind of problem you have to look for immediately when the symptoms begin, otherwise the evidence melts. It would certainly explain the revs slowly dropping of while choke is still pulled and after the car has idled for a few minutes. This condition would make for an over-rich mixture since not enough air can get through the ice-clogged venturis and throttle plates.