Hard engine shutdown

[aevansgatech]

Hey guys,

So once it's warmed up, my 79 carbed 2.0L runs pretty smooth. Occasionally, I'll have a rough shutdown though. It idles fine, but every few times it will continue to shudder for about 5 seconds after turning the ignition off. It's like it's completing one more combustion event.

My question is, does that mean my idle mixture is too rich or could it be something else?

[So Cal Mark]

idle speed too high and possible idle cutoff solenoid issue

[bradartigue]

Does your car have the original carburetor? If so it has a couple of devices that open with the drop in manifold pressure - and if they are not clean they may stay open, acting like a little throttle. At least one of these admits air, another one holds the throttle plates open slightly, and I think one does both at the same time. The best thing in my opinion for the stock carburetor on a 79, along with its manifold, is the shelf. Too easy to replace with something far better.

If you don't have the stock carburetor then you may simply have something staying open too long. Assuming the fuel cut-off solenoid is working correctly (it usually is) then you fuel coming in from another source. A leaking accelerator pump will keep delivering a little fuel (is your car hard to start in the morning, or smell like gas?) An incorrect idle linkage setting may do it as well.

Are you Atlanta, your sig line implies GA Tech...

[aevansgatech]

Thanks guys,

So here are my best answers to the follow up questions:

I believe the PO put in a larger carb than stock. The only real numbers I could find on it were 32/36 DFV, whereas stock should've been 28/32? It is a Weber though

I have the idle set a touch high (~1100) because if I drop it to 800-900 it doesn't like to start easily. I use the choke cable for cold starts, but after it's warmed up it idles along and runs smoothly.

And yes, I'm a ramblin wreck from GaTech! I live outside of Detroit now though

[bradartigue]

Thanks guys,

So here are my best answers to the follow up questions:

I believe the PO put in a larger carb than stock. The only real numbers I could find on it were 32/36 DFV, whereas stock should've been 28/32? It is a Weber though

I have the idle set a touch high (~1100) because if I drop it to 800-900 it doesn't like to start easily. I use the choke cable for cold starts, but after it's warmed up it idles along and runs smoothly.

And yes, I'm a ramblin wreck from GaTech! I live outside of Detroit now though

Nice carb.

Well you found your problem; the idle is high. The thing is still delivering fuel at shut-down. This isn't uncommon with the plates opening you're "telling" the carb to deliver more fuel. I'd get the idle sorted - 1100 I think is high and can be tuned through, either with better ignition timing or carb adjustments.

I'm in Detroit often, happy to come by next time I'm in and take a gander (an excuse to look at cars).

[aevansgatech]

Sounds good I'll try to dial it in at 900RPM and get the mixture right. I've been tinkering with that adjustment a bit lately

And definitely let me know if you're passing through. I'm roughly 30 minutes northwest of downtown