77 351w Fast Idle Sanity Check

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   77 Thunderbird
351w w/ 2150 carb

Long story short, I'm trying to set up my fast idle. I think this is a replacement carb, guessing a refurb, and it was never really set up beyond just getting the car in motion.
The car starts great - one pump of the pedal for setting the choke and a squirt, and it fires right off. Then I always had to feather the gas to keep it alive. Found that the fast idle screw had been left backed all the way out. Attempted to set it according to the sticker on the valve cover:

So, 2100 RPM on high cam at operating temp in gear neutral. There seems to be some debate online about whether the high cam is really the highest step or the middle step with the V. If I treat the highest step as "High Cam" it won't warm itself up, but if I treat the V step as "High Cam" it seems like the rpms are crazy for a cold motor.

What does work is setting the screw so that it idles at about 1350 while cold. Choke is adjusted to be more or less fully open when the temp gauge hits normal. Startup for me goes:
1. Pedal once (or twice if cold, etc) and release.
2. Start. Fast idle screw will be on the highest step, which I've see called the start position, idles at ~1800rpm and climbing.
3. After 15~30 seconds, I can then kick it down so the fast idle screw rests on the V, where it idles at 1350rpm.
4. As the motor warms, idle will gradually climb until I can kick it down. If I just leave it sit, it'll run on up to 2100rpm or so around when the gauge says it's fully warmed up. (This is what makes me think the sticker is calling the V step High Cam.)

This all seems ridiculous, but through trial and error I have found that, until very nearly fully warmed, 1350rpm is the bare minimum to keep the car going. I can sit there and feather it manually, or I can let it sit on the fast idle and gradually run away.

Is this for real? Does everybody else have this same experience with their malaise era V8?

Edited by derth - 06-February-2025 at 1:48AM

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derth Members Profile Send Private Message Find Members Posts Add to Buddy List New Member Joined: 06-October-2022 Location: VA Status: Offline Points: 35	Post Options Post Reply Quote derth Report Post Thanks(0) Quote Reply Topic: 77 351w Fast Idle Sanity Check Posted: 05-February-2025 at 8:26AM
	77 Thunderbird 351w w/ 2150 carb Long story short, I'm trying to set up my fast idle. I think this is a replacement carb, guessing a refurb, and it was never really set up beyond just getting the car in motion. The car starts great - one pump of the pedal for setting the choke and a squirt, and it fires right off. Then I always had to feather the gas to keep it alive. Found that the fast idle screw had been left backed all the way out. Attempted to set it according to the sticker on the valve cover: So, 2100 RPM on high cam at operating temp in ~~gear~~ neutral. There seems to be some debate online about whether the high cam is really the highest step or the middle step with the V. If I treat the highest step as "High Cam" it won't warm itself up, but if I treat the V step as "High Cam" it seems like the rpms are crazy for a cold motor. What does work is setting the screw so that it idles at about 1350 while cold. Choke is adjusted to be more or less fully open when the temp gauge hits normal. Startup for me goes: 1. Pedal once (or twice if cold, etc) and release. 2. Start. Fast idle screw will be on the highest step, which I've see called the start position, idles at ~1800rpm and climbing. 3. After 15~30 seconds, I can then kick it down so the fast idle screw rests on the V, where it idles at 1350rpm. 4. As the motor warms, idle will gradually climb until I can kick it down. If I just leave it sit, it'll run on up to 2100rpm or so around when the gauge says it's fully warmed up. (This is what makes me think the sticker is calling the V step High Cam.) This all seems ridiculous, but through trial and error I have found that, until very nearly fully warmed, 1350rpm is the bare minimum to keep the car going. I can sit there and feather it manually, or I can let it sit on the fast idle and gradually run away. Is this for real? Does everybody else have this same experience with their malaise era V8? Edited by derth - 06-February-2025 at 1:48AM

Rockatansky Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 30-July-2010 Location: On The Road Status: Offline Points: 6398	Post Options Post Reply Quote Rockatansky Report Post Thanks(0) Quote Reply Posted: 05-February-2025 at 10:46AM
	2100 rpm seems like a lot to me, and are you sure it's supposed to in Drive? i would think Park / Neutral
	72 GT Ute

78FordLtd2 Members Profile Send Private Message Find Members Posts Add to Buddy List Member Joined: 19-April-2021 Location: Canada Status: Offline Points: 184	Post Options Post Reply Quote 78FordLtd2 Report Post Thanks(0) Quote Reply Posted: 05-February-2025 at 8:52PM
	That is correct. 2100 RPM on fast idle step in neutral. Not in gear. Warm engine, choke off, set while in gear.

derth Members Profile Send Private Message Find Members Posts Add to Buddy List New Member Joined: 06-October-2022 Location: VA Status: Offline Points: 35	Post Options Post Reply Quote derth Report Post Thanks(0) Quote Reply Posted: 06-February-2025 at 1:46AM
	Sorry, I brainfarted. It's 2100rpm in neutral - that's what it says on the sticker, and that's what I've been doing all winter. Why in the world I typed in gear, bleh. It does seem high, but that's what the sticker says that seems to be what the car needs. I'd be curious as to what other people's stickers say vs what year their car is.

78FordLtd2 Members Profile Send Private Message Find Members Posts Add to Buddy List Member Joined: 19-April-2021 Location: Canada Status: Offline Points: 184	Post Options Post Reply Quote 78FordLtd2 Report Post Thanks(0) Quote Reply Posted: 06-February-2025 at 9:56PM
	I believe the high cam is the highest position for the choke. The kick down setting is the middle position...or "V" as you describe. From my own notes that I have scribbled down, my setting for my 351M is 1350 on the kick down and 600 fully warmed up in gear. Those settings are what the factory calls for on a stock 2 barrel carb. During warm up, it will idle about 2000 rpm when cold and then after a few minutes, I kick it down where it idles at 1500. I did kick the warm idle up to about 650 in gear where it seems happiest after the choke fully opens. At 600 rpm, mine tends to stall and run rough. That little tweak on the idle smooths it right out. That 2100 rpm may seem a little high but in the cold weather, the engine needs the rpm to warm up faste and keep from stalling. If it's a fair weather car, try a lower adjustment...say 1800 on the high cam. You might get away with setting the choke there.

Booyah45828 Members Profile Send Private Message Find Members Posts Add to Buddy List Member Joined: 28-February-2022 Location: Ohio Status: Offline Points: 163	Post Options Post Reply Quote Booyah45828 Report Post Thanks(0) Quote Reply Posted: 07-February-2025 at 3:33AM
	High step is the high cam setting IMO. What do you mean it won't warm up there? Do you have the distributor vac advance hooked up and is it ported or manifold? I've only had one stock cam'd engine with a 2v carb. Startup I'd do like you, with one pump and crank, then another pump to get it onto the v-step and then drive away. I think the vee step was like 1200 or so, but I can't remember if that was in park or drive. IIRC that engine liked closer to 700(in gear) base idle, and then 2000(in park) or so on high idle. The "v" rpm I don't remember 100%. It took a little tweaking every day to get it where I wanted it. The only real modification I did to that engine was to switch the vacuum advance from ported to manifold and bypass the high temp vacuum switch. I also kept that all connected(with air filter on) when setting base(hot) idle, but the decal stated to disconnect and plug the vacuum hoses when doing so. I'm not sure how you have your timing set up, so that might change how you set yours. IMO those decal instructions only apply if it's a 100% bone stock unit. If any changes have been done at all, throw those instructions out. I feel that if you're feathering it to keep it running while cold and on the v step, it needs more rpm. If it's slamming into gear when cold, then you need less. The RPM numbers really don't matter, so long as it runs without feathering when cold, and doesn't slam into gear and power through the brakes either.

78FordLtd2 Members Profile Send Private Message Find Members Posts Add to Buddy List Member Joined: 19-April-2021 Location: Canada Status: Offline Points: 184	Post Options Post Reply Quote 78FordLtd2 Report Post Thanks(0) Quote Reply Posted: 07-February-2025 at 10:38AM
	I did the exact same thing. I bypassed the TVS switch on the water pump and hooked up to ported vacuum on the carb and plugged the manifold vacuum port. I was having trouble setting setting the timing and it ran like crap. Problem solved and it eliminated a ton of useless vacuum hoses. Runs like a top now. These carbs were set up very lean and warm up was an issue from day one and required copious amounts of time running at fast idle before trying to drive away. If you tried to rush it, stalling out would happen or at best, poor drivability until it fully warmed up.

derth Members Profile Send Private Message Find Members Posts Add to Buddy List New Member Joined: 06-October-2022 Location: VA Status: Offline Points: 35	Post Options Post Reply Quote derth Report Post Thanks(0) Quote Reply Posted: 08-February-2025 at 6:18AM
	This is all giving me exactly the sanity check I needed. My last car with a carburetor was an 85 Chevette that I drove to college in 1998, so it's all new for me. I'm back around to believing the highest step is "high cam" and the V step is "kickdown" as makes the most sense in the first place. Vacuum advance is ported, and as near as I can tell the car is stock except for this kludged on carb. No idea what the timing is set to, though things run nicely once it's warm so I'm not too worried about it. Base idle had likely been set by ear-meter to what turned out to be about 500rpm - I added the Tach myself and then adjusted it up to the 625 on the sticker. When the weather's nice I'll get a timing light and a vacuum gauge on it and see what's actually what. For now, thanks to all of your replies, I'm happy to have it set to where it seems to be working, which is probably only half a turn of the fast idle screw up from what the sticker says anyway. This is a huge improvement from before, where my foot was the entire fast idle circuit. This all started, by the way, because I noticed the choke had burned out. Somebody had hotwired it to keyed 12v after swapping in an alternator without a stator terminal. So for now I've got a 12v Holley choke and a mystery alternator that nonetheless charges great. Thank you all again for all of the input!