Curious for any input. I have an AMC 4.2 L6 carby. She misfires

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Single bump and I'll let her 404.

>>16944862
How's the compression in that cylinder?

>>16945463
Good question, checking is free. I'll see tomorrow.

>>16945508
If it's low in the cylinder, odds are you've got a ring issue or your valves aren't seating. Or, you might have oil somehow leaking in or something.

Is there any smoke out of the exhaust?

>>16945533
Negative.
She's no smoker.

When it misses you can hear it in the exhaust and if you go wot there is a strong smell of raw gas. I might just go out and do a quick compression test right now.

How long does it take for the crust to build up on a new plug?

Does it run clean on a new plug for a little moment?

>>16944862

I've never seen a plug to that before.

How long does it take for a brand new plug to foul, have you tried measuring this yet?

>>16946181
It's only ever fouled that one so far,
I've had the car for 7,000 miles over 2 years.
I imagine not long at all because the car was fine up until a few months ago.

>>16946003
I put in new plugs ~week ago and it runs fine when cold, only once its warm does it start missing again. And the harder I run it the worse it is. It seems definitely temperature related to me.

I'm gunna do a compression test in the morning just to see, if it had low compression I could see it not getting a full burn, creating the build up on the plug, making the problem worse. And blow by could explain the raw gas smell.
If they're all similar I'll probably go throw plug wires at it. I'll check the resistance first, but I've never had any luck getting consistent readings on plug wires anyway.
I hope to swap in a 4.0 fuel injected one day, but emissions is this month, so kinda flying blind at repairing this considering I've replaced everything in the ignition system since I got the car. But hey, why not ask and see if someone smarter than me has a better idea, like kitkat's compression check.

>>16946242

Incomplete combustion buildup is carbon black. That's very different to what's on your number 6 plug.

I'm hedging a bet on a cylinder head or head gasket failure and that's burnt glycol on the plug.

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>>16946248
These the kinda people smarter than me I was talking about.
I'll report with the compression tomorrow.
Seems strange that there is no noticeable smoke when driving though.

>>16946259

And there should be for that much glycol.

On top of the compression test, do a leakdown test of the water jacket. That will tell you straight away if you are pumping coolant into the combustion chamber. If there are no external leaks and pressure is steadily dropping over time, chances are at the end of the test if you take out all six plugs and wind her over, one pot is going to spray coolant.

>>16946272
>>16946259
Another easy way to check for a head gasket coolant leak is to fill up your radiator to the very top, leave the cap off, and then crank your engine with the coil unplugged - this will ensure the engine doesn't fire for this test.

Keep cranking for 5-10 seconds, and watch (or get someone else to watch) to see if coolant is being pumped up out of the top of the radiator. If it surges out or starts spurting out, you know you've got a head gasket problem: the air compressed in the cylinders is being forced through a hole in your head gasket and pressurizing the coolant, making it flow out of the radiator.

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Check 'em.

>>16946433
kek

well done anon

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>>16946433

Haha, what the fuck man?

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>>16946433
well done

>>16946248
>burnt glycol on the plug

+1 for this. I had an engine loosing coolant internally and it did similar.

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Compression is fine. Almost made me sad for that to not be a problem.
I don't have a cylinder leak tester, and the check valve is in the hoses on a compression tester, so I'll get one.
Exciting I know.
Thanks.

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>>16946433

>>16946433
fucking checked

>>16946433
Czech'd

>>16947777
be my quads bf pls

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So leak down in.
I don't know why I got to harbor freight edition.
On Cyl 6 bubbles came out of the radiator for ~5 second then it quit and reads well now.
Cyl 2 just for comparison.

After performing it I drove around to try to warm it up and try again with it actively missing but it just refused to miss.
It's actually running better than it ever has right now.
In the past when heel toeing I would get a stutter/hesitation and I didn't get that at all right now.
Seems strange to me.

I would check the cooling system's leak down but I leak out of both heater core hoses and the thermostat gasket and the tool is $160 so I was going to wait and see my results on the cylinder first.

Also the plugs in the compression test image have maybe 20 miles on them.

ps I will post more anime girls with wat clothing poorly shooped on if I update again tonight.

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Well it definitely still misses.
And the leakdown hinted at headgasket between the water jacket and cylinder for a short time.
It's just strange to me that it happens intermittently, only when warm, and there's no smoke. But plug fouling and the leak down point to HG.
Thanks guys.

>>16944862
ignition timing, contact points. Carb

>>16951104
You don't always blow smoke with a head gasket failure.