I have a 69 cougar XR7 390 automatic with 24,000 original miles. My problem is, the engine idles great in park or neutral. When you shift it into drive with foot on brake, it’ll idle fine for a minute then the rpm’s slowly drop and then stalls. The carburetor was rebuilt. Not sure if problem existed before carburetor was rebuilt. All new vacuum lines were installed and transmission was rebuilt. Any ideas?? Thanks in advance.
Lets start by finding out what carb is in there? When the carb was rebuilt did you do any tuning on the carb after reinstalling on the 390?
ORIGINAL AUTOLITE 4300 CARB. NOT SURE IF ANY TUNING WAS DONE.
Stock ignition?
Everthing is stock. new wires,plugs, correct gap, new points condesor,coil.
Did you check all hoses for vacuum leaks? Any hissing/wheezing sounds?
I would check that choke gets on/off as it shoud.
After choke gets off, should idle at ~ 900/600 rpm in park/in gear. Mine tends to die too when adjusted to idle at lower rpm’s.
I would check if it behaves the same with/without vacum advance.
Fingerarcher, I am guessing you are either into bow hunting or bow shooting on the competition side? And using old school bows?
Anyway, having the same set up as you including the 4300 carb. I would suspect low initial timing. Of course all the other little things need to be correct as well. The thing in my mind is that if you are idling fine in park or neutral you can’t be that far off. Make sure your front vacuum port on the carb is going to your dizzy the back port on the carb goes to one of the heat tubes for the choke. So your idling at say 700-800 rpm in neutral / park and you pull the vacuum line off the dizzy and plug it you can now look at your initial timing. I have found my 390 likes about 10*. You can plug the vacuum back up to the dizzy and you should see the same timing as there should not be any advance yet. So my thinking would be you are low on initial timing. Could be wrong but I would certainly look at it.
I had this same problem with the 351W engine in my '69 XR7. It also had a (freshly rebuilt) Autolite 4300 carb. I replaced everything that you have listed to no avail. Was about to lose my mind and light the damn thing on fire. Then, on the advice of someone here, I checked the fit on what I was sure was a perfectly good distributor cap. Turns out that the fit was indeed just slightly off and it wouldn’t sit perfectly flat down on the dist housing. Bought a new, correct stock distributor cap and the car purred like a cat for the rest of it’s time (with me, anyway…). Sounds odd I know, but I swear that this is a true story.
Yes Splinehead you are correct. My son and I do compete in 3D archery tournaments. we have been competing for 10 yrs. We shoot compound bows with our fingers and are very competitive . We shoot recurves for fun and relaxation. I already have the timing at 10 degrees . I original had it at 6 and was having problems. I kept advancing it 2 degrees and it was getting better each advancement. The issue was getting a lot better. I might try advancing it a little more just to see what happens. I’m sure I will have to tune carb.
Nice hobby with the son. I can’t even think about using my fingers with my compound as it is at 85 Lbs. Enjoy that time with him.
Back to the car, I would continue to advance and see what happens(harmonic balancer may have shifted giving false readings) . Let us know how that works out. Not much tuning on the 4300 for the idle as far as I know, idle mixture screws can be tweaked and then depending on the year there may be an idle air mixture screw on the back of the carb. I don’t remember what years had it and didn’t. My screw on the back does very little but I have heard of some cars where that screw made a larger difference.
Oh, hey, I just thought of something, the gasket on the bottom plate sits just above the idle slot. The first time I had my 4300 apart and replaced the gaskets that gasket stuck out over the idle slot by about 1/16". I did not have it on the car yet but took a razor knife and cut that protruding gasket material out of both sides. Don’t know if that would have hurt my idle but I knew it would not be a good thing.
Good Luck.
Thanks for the info splinehead. Will let you know.