fuel is OK spark ( wires, spark plugs, coil) too the days before that I have had some symptoms like engine hesitation. Everything feels normal at higher speed or RPM, but runs rough when the engine is at an idle. the next day new problem : the motor doesn't stay at low idle speed and there was a lot of black smoke just before to shut down And now motor doesn't start . I checked the idle fuel adjustement screws and it was 5 for the left side and 3 1/2 for the right side but I can't find idle air bypass screw .
Seems extreme on the adjustment, try starting out at 2&1/2 out on both and adjust from there. Also are you sure choke is adjusted and working properly, that would contribute to the black smoke. How do your plugs look, (what color at the electrode)
the rear vacuum plastic part was broken . I fixed it and the motor doesn't start but not sure it's the problem because the motor smoked black and stopped before I fixed it.
First, let's think about that yellow plastic vacume fitting. From the photo with the red arrow I deduct someone has been very creative with the hose routing. Only one rubber connection belongs there. In the beginning, the yellow connector let the choke get clean air from a hole in the back of the carb drawing air from inside of the air cleaner gasket. That short rubber connector hose on the passenger side connected to a metal pipe that goes down into the choke stove on the passenger side of the intake manifold. That fresh air get's heated then sucked thru another short metal pipe going into the bi-metal choke housing on the carb. It is not uncommon for that system to get clogged resulting in a choke that want's to stay closed. Due to the age of that Ranchero and likely modifications I suspect you will find many out of place vacume hoses. Do any of you members have an unmolested engine you could take a photo of ? That carb is not a favorite of mine, I have replaced all of them on my engines but one with Holley carbs. Down in the bottom of the float bowl you will find a fuel enrichment valve that is vacume operated. It can become crudded up and stick open resulting in poor idle and mid-range operation = Flooding. Start with a set of new spark plugs and wedge the choke plate open then tell us what happens.
Which model carb is that? It resembles a Holley Economaster, but I can't see a 429 running on one of those.
sorry for my english , it's difficult for me to explain with the good words. I write like a little boy. so I checked the choke and found a screw . I adjusted to keep the plate open and the motor started immediately. thanks for your help. so now I still have my idle hesitate problem. After 6 miles, 2 times the motor stopped after a big hesitation at low idle. I looked the yellow switch and there is only one hole . The other side, where there is a vacuum line which comes from the air box , hasn't hole. So I don't understand why the line is there and where it needs to go ? no found other vacuum hoses
Thought I had mailed this earlier, but now I see that Ribald has answered your question. Here's some more info -- Hi, Cedalice ... that vacuum line in question is part of the carburetor choke pre-heating mechanism. In short, a small vacuum source in the carb (behind the choke mechanism) pulls air through that line, which takes a detour through a depression in the intake manifold, before picking up semi-clean air from inside the air cleaner housing. If everything is working right, the intentional vacuum leak is compensated inside the carb. Nothing to adjust, just be sure the external tubing doesn't leak. Your carb (4300) has an internal vacuum-operated piston which is supposed to unload (partially open) a closed choke plate, which will allow the motor to run until the bi-metal coil inside the big black choke housing on the carb takes over and fully opens the choke plate. Some versions of that carb include a couple wires to the carb that also help to preheat the bi-metal part. If it was working correctly you'd see the cold (shut) choke plate open a bit as soon as the motor begins to make vacuum, i.e., as it starts up. This will also fiddle with the linkage on the carb to adjust the idle speed. My suggestion is that you find a replacement modern carb. Then you can remove and toss that hose assembly along with the 4300. Other wise get a kit and do a home rebuild of the carb. As for your idle problems, I suggest that you find replacement gaskets (two sets beneath the carb), and then remove the carb to closely inspect the existing gaskets for air leaks. That model of intake manifold pipes exhaust gas through passages inside the head to route them to the EGR valve mounted behind the carb -- and they are prone to break through which will give you a leak you can't adjust out. Find the replacements first, in case you have to scrape off the old gasket. Once it's running at idle, you can test the EGR for leakage by manually opening the diaphragm, which should kill the motor and then return to normal when you stop manually forcing it. But who knows if the ancient valve leaks? Only way to be sure is to replace it. Welcome to old tech from the beginning of the smog fight era.
Ha, I had looked through some photos, found my friend's two 4300-Ds, and realized that your carb is the same. I have a Motor and Chilton manuals from that time that include pages on the 4300-D; if you give me an email address, I'll photograph the pages and send them to you.
