I think I'm confused. Lately, I've noticed that my engine on start up, will spin freely, but not fire quickly. On shut down, I turn the key off and the engine will free wheel for a second before coming to a complete stop. It's not the "turn the key on and it makes a half a rotation and fires then turn the key off and engine stops instantly" kind of thing. This has been going on this past year. I want to address it over the winter. I've tried adjusting the advance curve, adjusting the idle mixture screws, adjusting the fuel pressure up and down. Ignition is a Digital MSD 6AL. Distributor is a Mallory with Pertronix conversion kit that I've used for years with no issues. The kit is new. Replaced it last spring and ran it all last year. Timing is all out by 1500 rpm at 35*. Initial is at 13*. Plugs 3924's gapped at .045". Carb is a 1050AN Quickfuel. with 84P-92S jets. air bleeds 73/31. I can't put my finger on when this all started, sorry. Any suggestions????

Sounds like you've checked the basic things that I would have

Any chance the quality of the local pump fuel is getting worse?

Some of the later digital MSD race boxes, not sure about the one your using now, won't fire the coil until the 2nd revolution to help the race motors get several crankshaft revolutions on those motors so they won't kick back and break the starters.

Slow to light: how good/clean/tight are the Grounds ?
I've had very few engines that would light off immediately unless they were already warmed up.
Continuing to spin: ya got me on that one, as there's nothing in the description that indicates dieseling.

Y'all have probably forgotten more than I know...

I have grounds from frame to block. Grounds from firewall to block. Battery to frame. You might say that I have grounds to grounds😂😂

Not dieseling. Just not an instant shut down. Not a run on either. Just not an instant shut down.

Maybe ignition switch failing? I would monitor ignition power vs key position.

Are you running electric fans?

Brand new ignition switch. No electric fans. Just a Jag clutch fan.

So same before and after the new switch? Just saying I would check and confirm because new isn't always good.

Was having the same issues and others before changing the ignition switch. The new switch didn’t change anything but my piece of mind that the switch wasn’t an issue. The engine eventually starts and runs strong.

A few things I would check that have not been mentioned:

1) I would check the i tegrity of the floars in your carburetor. It would not hurt to change the needle&seat assemblies as a maintenance item.

2) I would 2x check for a vacuum leak. Verify the base plate to main body screws are tight, etc. Not all vacuum leaks come from the manifold.


My guess is this is not ignition related. One way to peoce that is to ensure there is not output from the MSD is switched off. You could test that with the white points trigger wire and a spark plug plugged into the coil wire.

The floats are good. The float level is steady as a rock. The MSD is something that I haven't thought of. If I recall, with my old 6AL I didn't have this problem. Maybe explain in detail your recommendation for checking it.
No vacuum leaks. I checked that.

stick or automatic ?
if automatic, how does it shut off in gear [third or drive] ?
i know you said the MSD distributor works good, but could the weights be sticking a little in just one spot ?

Stick car. I’ve bin thru the distributor, everything is free no sticking weights or anything else.
I’m thinking maybe to lower my idle speed. It’s at 950 now. Not sure if that will work cause if I remember, the engine had a hard time idling anything lower than that.

Hmmm...you might find that closing the butterflies works for the shut-off.
Heck, might even help the startup.

Okay, an update!! As far as my issues, it was something stupid. Low battery voltage!!!! I also closed the idle mixture screws a bit. From 1 turn to 3/4 turn out. Everything good again. Thanks for all the input. 👍