I can believe the carb is adjusted improperly, but try to help me understand this. I'm not challenging your knowledge, as I believe you know these cars a lot better than I ever will, but I would like to understand so I can get my own carb issues worked out eventually.
How can it be the accelerator pump, if the problem happens before he ever touches the gas pedal? I am more knowledgeable when it comes to the small flatslide and bsm carbs on MX bikes and quads, which I think the same basic principles apply to. On those, the accelerator pump only works when the throttle is applied, and the harder the throttle is jabbed, the more fuel it squirts down the throat of the carb. In my experience a non working or weak accelerator pump causes hesitation when the throttle is applied, and stalling if the throttle is jabbed hard enough, but the accelerator pumps have nothing to do with the idle circuits or choke circuits. The idle screw settings (speed, fuel) seem to be a more likely cause to me.
Sorry for replying to you so late, WoodenBirdOfPrey, but I've been writing a reply to this message for two days now. I've written 10 pages so far. It's a mess of information and I'm working now to organize it and make it more concise. I’m not going to post that stuff here. I’m working to create a new thread in the “how to” section of the forum.
This is the gist of what I’ve been writing about in detail.
First thing you need to know is that usually when we say our engine “is at idle” we simply mean that there is no load on the engine. That can be very confusing because in carburetor terms “at idle” and “at throttle” simply refer to how the air and fuel get into the engine. The throttle plate is designed to touch the side of the throttle bore, completely stopping air or fuel from entering through the throttle body. When the throttle plate is up against the throttle bore there are holes above and below it. These holes lead to tubes that get closed or opened up by the pointy end of the “Idle Adjustment Screws” located at the bottom front of the carb. When your engine is “at idle” the only source of air and fuel is supposed to come through those holes. When your engine is “at throttle” the air and fuel comes to the engine through the bore of the throttle body.
Next you need to know that I've purchased several Eagles at scrap value because the owner could not get them to stop stalling. None of them had any mechanical issues. All of them had the Accelerator Pump setting massively off. There is no way to get the Carter BBD Carb to run properly until you've tackled that setting. It is critical to the BBD but inconsequential to most other carbs out there. Most people don't even know it is there. The more experience you have with other carbs the less likely you’ll pay it any mind. I blame this setting for the vast majority of Eagles sent to the scrapyard for running poorly.
I didn't know it was there either. I couldn't get my Eagles to stop stalling along with everyone else I met, including my professional mechanics. I managed to get my Eagles to run well by turning down the idle screws and a third screw at the throttle cable. Turning the third screw would make the idle RPM increase and turning down the idle screws would make it decrease back to what sounded normal. What I was actually doing was putting the carb at “low throttle” instead of “at idle.”
The Accelerator Pump shoots gas into the engine in an attempt to smooth the transition from idle to throttle. It works like the trigger of a water gun. Every time you let go of the gas pedal and push it back down it is like pulling the trigger of a water gun. The Accelerator Pump shoots gas every time you push the pedal but then it stops shooting gas until the next time you let go of the gas pedal and press it again.
If set properly your carb goes to idle when you let go of the gas pedal. The throttle plate touches the side of the throttle body and the holes above and below it are the only source of gas and air. When the gas pedal is first pushed down the throttle plate moves away from the throttle bore, letting a rush of air into the carb all at once. At exactly that moment the Accelerator Pump shoots gas to balance out the rush of air and maintain the ideal fuel-to-air ratio. Once the throttle plate has rotated just a few degrees it no longer needs assistance and the accelerator pump stops shooting gas until the next time your foot comes off the gas pedal and returns the carb to a state of idle.
If you keep the carb at “low throttle” and never let it get to idle you no longer need an Accelerator Pump. My Accelerator pump was still working properly but it wasn’t needed to smooth the transition because the carb was never reaching a state of idle. This created terrible hesitation and flooding as I drove the car. I compensated by fancy jabs of the gas pedal.
I drove it like that for a good long while. I then discovered that I could reduce the hesitations and flooding if I played with the mysterious setting hidden under the cover of the carb. I didn’t know what I was doing but I was essentially turning my Accelerator Pump off. Once I did that there was no hope of getting the carb to run right. You can adjust anything and everything else but there is no way for it to run correctly until you return that setting where it belongs.
In the course of my troubles I ran into the exact same problem posted here. The car would sound great in Park but instantly stall when put into Drive or Reverse.
I did drive the car for a long time with the BBD carburetor totally set incorrectly. I figured out how to get it to run very smoothly and to not stall. I accomplished this by essentially disabling the Idle circuit with the use of that screw at the throttle cable. The car ran great but the fuel mileage was obnoxiously low. I was getting about 16 MPG. Once I learned how to tune the carb properly along with the Accelerator Pump setting I consistently reached 25 to 27 MPG. I never had stalling or hesitation problems again. The Carter BBD was actually a very well designed carburetor that AMC relied on to make their cars marketable as economy cars. The difference was huge once I figured out how to get the BBD to work the way it was supposed to work.
I suspect the person who started this thread installed their new carb with the Accelerator Pump set incorrectly from the box. They ignored that setting and then tuned the carb to run well without it. I suspect this because it is exactly what I did and it is exactly why I've purchased so many Eagles so cheaply. Indeed I suspect the vast majority of AMC Eagle owners are driving their cars poorly tuned. The first step in fixing it is fixing the Accelerator Pump setting. Then you can back off the throttle cable screw until the engine is totally back to idle and then start the tuning process from scratch from there.
If the car ran well after it was tuned improperly and then suddenly developed this problem I suspect a minor vacuum leak compounded on top of the improper tuning. A vacuum leak introduces air into the engine. When you make a car engine idle smoothly and quietly at low throttle you usually accomplish it by leaning out the mixture with more air than fuel. If the car already is running with a poor mixture a minor vacuum leak can have devastating effect on the engine. If you have the car tuned properly a vacuum leak will not have such a drastic effect.
Topic: stalls when put in gear (Read 17082 times)