My '85 MGM, "Maisa"

[DerekTheGreat]

I drive a Lincoln. With it's sophisticated SEFI setup, I don't need to worry about such rabblerousery.

[Arquemann]

I put the magic ziptie back on, I hereby declare the carb fixed! AFR on harder acceleration is around 13.5 and it lowers to about 13.0 at high rpm. Perfectly fine for an economy-tuned Holley. I guess I've got a ~285 cfm 2-barrel now (actually ~400cfm if we go by 2bbl rules). Not that I needed the secondaries anyways...

The ticking sound I'm hearing is unresolved. I found a leak on the Y-pipe and patched it with exhaust putty. After a short drive I couldn't hear it, but after romping on it the tick was back. Not sure if my putty patch blew out, or the tick is coming from somewhere else, or if it even is an exhaust leak. Though its clearly the louder on the left side and from underneath around the cats area.

[Arquemann]

Hey guys, did you know that exhaust manifolds get like really hot?

Anyways, I couldn't feel or see an exhaust leak anywhere, but I can still hear the tick (which sounds softer now, more like an exhaust leak). I got a mechanic's stethoscope, seems like it might be coming from around the heat riser valve. I guess I'm pulling that apart next. Dunno what to put there considering there's no gaskets or donuts on these. High temp RTV?

[gadget73]

should be a taper on the bottom of the manifold and a matching taper at the exhaust pipe. Any chance its the shaft for the heat riser leaking? Those can wear basically like carb throttle blades. I don't think that would be fixable with RTV, but if you wire it open maybe you could pack JB Weld around the shaft if that is where the leak is.

[Arquemann]

should be a taper on the bottom of the manifold and a matching taper at the exhaust pipe. Any chance its the shaft for the heat riser leaking? Those can wear basically like carb throttle blades. I don't think that would be fixable with RTV, but if you wire it open maybe you could pack JB Weld around the shaft if that is where the leak is.

The manifold and top of the flapper valve are machined flat. Bottom of the valve has the taper for the exhaust pipe. RTV could work for the flat flanges and maybe help with the taper connection. I thought about finding a suitable exhaust gasket for the flat flanges, but all local parts counter guys have become completely useless unless you have a plate number or make/model for them.

I might gut the flapper valve and plug the shaft holes if I can be bothered. Would eliminate the restriction and the possible leak spots aswell.

[WagonMan]

The top of the valve is indeed flat. The bottom has a molded in flange. There is a tiny cover on the end of the shaft, ( like a tiny freeze out plug) that may be rotted away. WagonMan

[Arquemann]

Original exhaust manifold studs are holding on for dear life, but surprisingly the nuts came out fine.
Apparently I had used some of that exhaust putty on the flat flanges between the manifold and valve, no sign of leaks but it is a bigger possibility since there was putty to blow out.

Gutted the flapper valve and removed the dashpot off the side, plugged the open shaft hole with a pop rivet and stuffed some exhaust putty on the outside of both sides for extra insurance. Might've gained atleast 3/4 of a horsepower with flapper valve out of the way. Maybe more if I was handy with a carbide bit since there's a sharp step inside, but the ID on the tapered bottom side is only 1.75". Sure was easier to get it back in place without the vacuum dashpot.

I did get an actual gasket for the flat flange and did a light smear of high temp copper RTV on the tapered flange.



I should be getting an oil filter tomorrow so I'm leaving the car on the ramps for now. Also gives time for the exhaust putty to cure.
If this shitfuck still ticks from somewhere, I'll remove the headshield off the cat. Its actually screwed together instead of riveted, so there is a chance of getting it back together.

[Arquemann]

Well this shitfuck still ticks indeed, I took off the cat heatshield, can't see anything indicative of a leak under there either, even though the cat is quite crusty. I wonder if the insulation is asbestos...

I spent another ~30 minutes poking around with the stethoscope and I can't find shit. Poking on the exhaust manifold, on a hot engine I can hear a tick on every cylinder, but cylinders 7&8 seem a bit louder. What I'm most likely hearing is the valves or exhaust pulses. The ticking can be heard poking on the end of the manifold, but the other side does it aswell. Cannot hear a tick anywhere on the catalysator below the flange.

Seems like I can't do anything about it. I guess I'll leave it be until something changes. I've got an inspection coming up in about 3 weeks.

[gadget73]

maybe try jamming the smoke machine in the tailpipe to see if you can see anything

[Arquemann]

maybe try jamming the smoke machine in the tailpipe to see if you can see anything

I can only hear the ticking with a properly hot engine / exhaust. Whatever spot that may or may not be leaking is dead silent on a cool/cold engine. Besides the smoke machine that I had loaned wouldn't have had the ass to push smoke through the exhaust and out of any tiny holes. If I had a proper automotive smoke machine, I'd be atleast worth a try.

[GMUE03]

Any possibility it’s a rattling PCV valve? (If you still have one).

[Arquemann]

Any possibility it’s a rattling PCV valve? (If you still have one).

My PCV valve is on the valve cover behind the alternator, it's not gonna sound like that under the car.

[GMUE03]

Ah right, it’s not at the back of the manifold like later cars.

[gadget73]

yeah metal PCV valves in multiport cars can make a strange rattle noise that sounds like something is broken.

[Arquemann]

I've been banging my head against a wall and it doesn't work.

Drove to friday's cruise night just fine, went lean on the way home. Literally just sitting for a couple hours and decided to be lean. Immediately noticed it as it wouldn't idle properly when cold. Hot idle went from 13.5 to 14.5, very light throttle is a bit unhappy and the jerky decel naturally came back aswell.
My magic ziptie had gone a bit limp from the engine bay heat. I replaced it and the magic is gone. Idle was still lean and the decel was jerky.

Yesterday the idle was fine again, no jerky decel.

Today I the idle was lean-ish and the decel was jerky only occasionally.

I put a new exhaust manifold gasket for the driver side. Didn't fix the tick. Mainly did it just to rule it out for some peace of mind.

EDIT: Today (tuesday) I took the car to mechanic friend of mine. He's quite sceptical of it being an exhaust leak after hearing it and taking a look underneath. Would make sense that I can't see anything indicative of a leak either. So what is it? No idea. "Dunworryaboutit", I guess that's what I'll do because I can't find anything that'd make the noise...

Also the carb threw another curveball at me
I had removed the zipties that did and did not do something or anything, put a small clamp on the secondary actuator rod to keep them shut. Since its been idling kinda lean, I fattened the idle a wee bit to get it idling smoother. End result? It idled even leaner than before, unusually smoothly until it decided not to idle smoothly at all anymore.
Parts store should be getting a load of Edelbrocks in a couple weeks. I think one of those 500cfm AVS2s might be mine soon.