My '85 MGM, "Maisa"

[Arquemann]

Food for thought: What's the vacuum gauge showing while it's surging? Is it by chance switching between the idle circuit and venturis? Might need to fatten the idle mixture.

I'll specify, just in case, this surging happens intermittently, only in gear at idle when the ac compressor kicks on. Surging peaks every few seconds.

Haven't the faintest clue, I haven't had a vacuum gauge hooked up. AFR gauge doesn't seem to show anything directly related to the surging.
Whaddayamean by switching between the idle circuit and venturis?
Idle afr is already pretty rich, about 12.5 in park with ac off. Around 13-13.5 in gear and somewhere around 13.5-14 in gear with the ac kicked on. I guess it can be richer under loaded idle conditions, but as it sits all scenarios are quite smooth-running. I got 15° of base timing too, so the idle is a touch high without any load.

Still haven't checked the belt, I had a thought that maybe the compressor clutch could be slipping, but having such consistent surging and no other symptoms, I doubt it.

[DerekTheGreat]

Whaddayamean by switching between the idle circuit and venturis?
Idle afr is already pretty rich, about 12.5 in park with ac off. Around 13-13.5 in gear and somewhere around 13.5-14 in gear with the ac kicked on. I guess it can be richer under loaded idle conditions, but as it sits all scenarios are quite smooth-running. I got 15° of base timing too, so the idle is a touch high without any load...

I had that problem with my Fury when I tuned it's Holley. The base idle was such that it was pulling fuel from the idle & transition circuit. I don't remember if it was actually pulling fuel from the boosters, maybe.. It's an issue that crops up sometimes, air bleeds in the throttle valve help. When that happens, it can cause weird surge issues. My case was two-fold: It was pulling fuel from the idle & transition circuit and then the power valve in it was wrong- it was always open as my engine didn't make enough vacuum at idle to keep it closed. That caused transition problems, had a stumble that took me awhile to get rid of.

I reviewed some stuff from this site: CC Tech: The Operation and Tuning of a Holley Carburetor - a Modern Twist on Old Tech - Curbside Classic

"
First is the idle and transition circuit, often simply called the idle circuit. This circuit controls the fuel delivery at idle, but also the transition period before the main circuit starts to pull fuel. While many think that tuning the idle circuit only affects the idle, this is not true. At very small throttle openings the engine is fed by both the idle jet and the transition slot. This circuit is fined tuned with the idle mixture screws, screw in or out to lean or richen. On some Holley’s the idle screws are only on the primary side, but others, have them on the secondary side as well for a total of four idle screws. If the idle screws are unable to properly tune this circuit, this can be adjusted by changing the idle jet size or the idle air bleeds (more on air bleeds later).
"

Might be your problem, might not. Perhaps the timing is swinging and causing the surge? That idle is indeed rich. How's the smell at the tail pipe? Wonder if that's rich enough to make your eyes water up.

[Arquemann]

I had that problem with my Fury when I tuned it's Holley. The base idle was such that it was pulling fuel from the idle & transition circuit. I don't remember if it was actually pulling fuel from the boosters, maybe.. It's an issue that crops up sometimes, air bleeds in the throttle valve help. When that happens, it can cause weird surge issues. My case was two-fold: It was pulling fuel from the idle & transition circuit and then the power valve in it was wrong- it was always open as my engine didn't make enough vacuum at idle to keep it closed. That caused transition problems, had a stumble that took me awhile to get rid of.

I reviewed some stuff from this site: CC Tech: The Operation and Tuning of a Holley Carburetor - a Modern Twist on Old Tech - Curbside Classic

"
First is the idle and transition circuit, often simply called the idle circuit. This circuit controls the fuel delivery at idle, but also the transition period before the main circuit starts to pull fuel. While many think that tuning the idle circuit only affects the idle, this is not true. At very small throttle openings the engine is fed by both the idle jet and the transition slot. This circuit is fined tuned with the idle mixture screws, screw in or out to lean or richen. On some Holley’s the idle screws are only on the primary side, but others, have them on the secondary side as well for a total of four idle screws. If the idle screws are unable to properly tune this circuit, this can be adjusted by changing the idle jet size or the idle air bleeds (more on air bleeds later).
"

Might be your problem, might not. Perhaps the timing is swinging and causing the surge? That idle is indeed rich. How's the smell at the tail pipe? Wonder if that's rich enough to make your eyes water up.

I haven't touched the transfer slots since I got the carb from the swap meet and did the initial setup years ago. Set them to squares like you're supposed to. The idle is set kinda rich because I was just tuning for smooth running. I think I'll experiment with the idle mixtures, it might help the surging.

Went through all the vacuum stuff, HVAC still has a tiny leak but no leaks otherwise, also hooked up a vacuum gauge. It's not very steady, constantly bouncing between 16-18 inHg, but no dips or deviations. Dunno if that's a bit low or not, but that and the unsteadiness might be from the rich mix, I don't think I'm having any ignition issues.
Ignition timing is constantly going back and forth about 2 degrees when looking with a timing light.

No bad smells I've got 2 working cats and I like it.

[Arquemann]

I leaned out the idle on friday and it has not had the idle surge since. A couple times there's been something ittybitty about the idle, maybe it's trying to surge a little bit. I'm very doubtful that actually did it, but maybe it did. Engine still takes an awkwardly long time to settle to idle when coming to a stop, and sometimes feels like a bit like surging just before coming to a stop.
Cool.
Uncool is that I've hit a dead end with the carb tuning. It's meh overall, cruising speeds a bit rich and light throttle is lean. Basically the same situation as a month ago, but both ends are less extreme. As long as light throttle and tip-in behaves nicely in all temperatures, it's time to take off the wideband.

Also I have located 3 of the wheel covers that I want, seller has them stashed away, which will take a week or two for him to get them, but I'll wait.

[DerekTheGreat]

I'd want it the other way, cruising a bit lean and light throttle a bit rich. Mo' MPG & longer plug life, 'yo. Probably easier on the cats, too.

[Arquemann]

I'd want it the other way, cruising a bit lean and light throttle a bit rich. Mo' MPG & longer plug life, 'yo. Probably easier on the cats, too.

Yeah, I know, I'd make it so if I could.
Cruise speeds are affected by both transition and main circuits, and light throttle driving is mainly transition. If I drop main jets by 1 size, acceleration goes way too lean. If I fatten the transition circuit, light throttle gets better, but cruising speeds go even richer, if I lean out the transition circuit, cruise get only slightly better and light throttle goes too lean.
Lean light throttle driving is half coasting, being lean isn't too bad since the engine is under very little load and so far no driveability problems. Cruising/highway speeds the engine is under more load, so ~14 afr isn't too bad, at 15 aft those speeds weren't the smoothest anymore.

I finally get why generally Holleys are regarded more "race" carbs and Edelbrocks and Rockorchestras are more for cruising. Holleys are harder to tune for optimal cruising, whereas heavier throttle mixtures I got spot on with a snap of my fingers. If someone were to hand me an AVS2, I'd probably buy a tuning kit for it, but for now I'm staying with the Holley I've got. That 1200€ FiTech kit is kinda tempting though.

[Arquemann]

It did surge once today, while the engine was still warming up, didn't do it after the engine got warm.

Aaaaand the filler neck seal is pissing gas again... For fucks sake the filler neck seal is like 3 years old.
Popping the gas cap didn't make noise so I don't think the vent is stuck, but won't hurt to give the vent line a suck.

[gadget73]

I'm sure it will feel better at least.

[DerekTheGreat]

...Rockorchestras...

I guess I'm a masochist, as I'd rather have the Holley. Could be because that's what I know and it could also be everyone else just slaps a "Rockorchestra" on and calls it "done" with a smug look on their face. Not a fan of smug.

[Arquemann]

Tank vent seems fine, charcoal canister isn't restricting airflow either. Filler neck seal had gathered some dirt and sand around the filler neck, any movement probably caused the dirt to chafe and tear at the seal. Cleaned it all out and generously smeared black rtv on the seal lip around the filler neck. Hopefully it seals, because it'll be fun having to remove it now.

I guess I'm a masochist, as I'd rather have the Holley. Could be because that's what I know and it could also be everyone else just slaps a "Rockorchestra" on and calls it "done" with a smug look on their face. Not a fan of smug.

Maybe just bolting one on and firing it up gets ya pretty far and people like that, understandably so. I couldn't leave one of those alone even if it ran fine right out the box.
I got a Holley because the huge fucking carbs are cool and macho and Ford used Holleys on the big blocks. Also I Holley tuning seemed more straightforward.

I'm pretty sure my tuning "problems" are due to me having a asthmatic 302 that flows very little air at idle and low rpm and having a single 2" exhaust thats probably restrictive at higher rpm. And 570 cfm of carb on top.
Trying to wrangle the last 10% to have good driveability and still leaned out enough to get some MPG squeezed out.

[gadget73]

if you haven't sorted out your timing advance stuff, might want to do that first.

[Arquemann]

I have put black tape over the wideband gauge to stop me from staring at it all time, drivers very nicely by feel.

The engine idles smoother now with more and more driving after the rebuild. I might try leaning out the idle a bit more since its not as shaky anymore. It's still slightly on the rich side and the light idle surge comes and goes once in a while.

I'll start playing with the distributor recurving once I get my Volvo somewhat back together.

Managed to get the wheel covers I was looking for. Paid a bit too much in my opinion, but still cheaper than buying anything from outside of Finland. Now I have 5 matching caps, one is kinda rough, one is alright and the 3 new ones are pretty nice.

They make the wheels look smaller, but I still love the look and the fact that these wheel covers don't fucking creak and groan. Put them on just before the cruise night:

[DerekTheGreat]

Your car looks great.

[Arquemann]

No wonder it felt like the mechanical advance wasn't doing much, the other centrifugal weight is missing completely... #Cardon't

I have spare distributor that I can salvage a weight off of, maybe both to make sure they're the same. Another issue is that the advance plate is 16L / 21L, aka 32° or 42° of mechanical advance. Both way too much even with 10° of initial. Unfortunately the spare dizzy has a different diameter shaft, so the slot plate thing won't fit on the one in the car. Guess I gotta weld a slot and make it smaller. Should probably aim for a ~20° slot, I can play with initial for more.
I don't want too much since the mechanical advance will probably come in early and I don't rev this to the moon anyways. Using both the mrgasket 925D springs is supposed to be all in between 2000 and 2800rpm, 2800rpm would be great, earlier sounds really early. Gonna play around with how the springs feel, maybe use one aftermarket and one light OEM spring. Getting access to the springs is annoying and tedious, so I don't feel like I'd want to do it often.

[gadget73]

This is one place that the GM HEI distributor has it all over the Duraspark stuff. Its right on top under the rotor, takes longer to get the cap and rotor off than to change the springs.