Alright, it's an old car with an untouched 390fe. I've rebuilt the original Autolite 4100 carb and runs great for its age. So, I don't want to be too picky or critique it but I cant figure out why it sometimes wants to stall when stopped. The RPMs plummit low but when I hit the gas to go, its all good. Is it getting flooded or could it be that my secondary floats set too high?
I hear ya 31, but it would do it all the time, right instead of doing it every now and then? Maybe vacuum leak coming from the booster?
Did you replace the anti-stall dashpot? That could very easily do it. You could check for general vacuum leaks while you're tinkering with it. Bob
Thanks bob, no I didn't replace the dap shot because it didn't have it when I bought it. Man, I've check all around the engine for vacuum leaks and nothing comes up. Maybe I should install one.
Your carb may not have had one, been a while since I dove into one. I had one go bad on my '64 wagon with the automatic and it was doing what your car is doing. I would have to look at a manual to refresh my memory. The acid test for vacuum leaks: With the car warmed up & running and air cleaner off (all vacuum hoses plugged, if any..), place a hand over the carb airhorn, like you were trying to smother it. If the idle picks up and it smooths out, you have a vacuum leak. If it tries to die, no vacuum leak. Bob
Intermittent problems are a challenge. Especially finding them when its not screwing up. Since things move in an engine compartment around it could be to. I'd be looking for brittle hoses first the leak when flexed but OK at rest.. Check any pots and the booster. Like I said that be the most common and easiest. If it was a mechanical problem it would be there all the time more often than not. Classic symptoms of a vac leak - goes lean and a goose on the throttle hits the accelerator pump giving extra fuel for the moment and she recovers. Sometimes when you see horse tracks it could be from a zebra but that's not the norm.
Thanks guys ... Bob, I checked for vacuum leaks by the method you told me and it bogged and stopped the motor ... so the result is no vacuum leak. Yes, supposedly all Autolite 4100s were design with the dapshot. I'll try to find a dapshot for the carb and install it to see if it remedies the issue. Anyone know where I can find one?
If you did this while the problem was present and got those results that's one thing and you've reached a solid conclusion.. if you did this without the problem present or car about to stall then its really inconclusive to the problem. Did it do this before you rebuilt the carb or is this new problem that arose after the rebuild
No vacuum leak, good! Although they're usually easy to remedy. I did a quick search and came up with Standard Motor Products D5-35F. I would hit a local parts store like Napa to see if they have them or another brand like Echlin. Does your carb have the bracket to attach the dashpot? Bob
Thanks again ... 31, yeah I think I have a solid conclusion. The issue existed before and after rebuild. Bob, Thanks for the info ... No, I don't have the brackets so, I'll have to find that as well.
Been a while since I've seen one, in the pic below its at the lower left. Whatever bracket, its probably the same on the equivalent 2BBL... or maybe the bracket is part of the dashpot. This link shows it pretty good. http://www.mustangmonthly.com/howto/mump_1012_autolite_4100_carburetor_installation/photo_16.html
As far as I know a dash pot eases the throttle plates closed so they don't slam shut. This allows the engine a chance to stabilize from the transition of heavy throttle to none when you lift your foot & is only active on very low throttle position to closed in the descending direction. A damper just like your screen door has. Of course if the carb is supposed to have one it should be there. But don't see how that would help idle when stopped. Its more to keep from stalling on an exit ramp I'm interested in how this turns out.
Doesn't sound like a dash pot problem to me. Sounds more like possibly a combination of a little bit of timing, and a bunch of carb idle/air, idle speed adjustment. Sounds like idle fuel air problems that go away as soon as you break out of the idle cicuit. While you're checking, also look at float level, as a high float level, leaking needle/seat can cause flooding out at idle, but run good off idle.
I have adjusted mine both ways didn't seem to help a fella told me it could be a vacuum that goes down to the trans?
Check the vacuum advance. I get lots of old ford engines in my machine shop. When we get them on the dyno we often find the vacuum diaphragm has been leaking.
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