Spark Control Valve or Load-O-Matic

I'm fighting a '66 170 motor with an Autolite 1100 and Load-o-Matic distributor. Truck wants to die unless the choke is on. It's wanted to die out once warm with the choke pulled obviously. Timing is at about 8 degrees, but when revved up I'm getting no advance on the timing. Bad vacuum advance diaphragm on the distributor, maybe? Will a spark advance valve blow out like a Holley powervalve on a backfire? Carb rebuild was recent, but wondering if an backfire got it.
Vacuum is solid and steady at 20 lbs. Running Pertronix which seems to be functioning properly. Thoughts?

LOD dose not work the same as a vacuum advance! Check out this link for good basic info on the LOD system.

http://classicinlines.com/Loadomatic.asp

LOD works off of the load on the engine its a combo of manifold and the carbs Venturi Vacuum so just revving the engine is not going to advance it. The answer to your other question is yes the units can go bad, but again not in the same way that a Holley power valve is damaged by a backfire. Have you done a check for vacuum leaks, and set your idle RPM correctly? You might also try advancing the timing lead a few more degrees. Good luck

Seems you could check the vacuum being put out by the SCV by disconnecting the connection at the distributor and measuring the vacuum in different load conditions.

I had a similar challenge with an Autolite 1100 on my 200- any chance you have a vacuum leak somewhere? Also, make sure the choke is actually opening when warm (one of the problems on my 1100 was a bent spring in the choke that would sometimes cause the choke to close when warm- causing stalls when hot).

End of day, swapping out the stock distributor (and the SCV) for an HEI-type distributor really improved overall performance across the rpm range for my engine.

One thing to check. Inside the Autolite 1100 is a built in power valve(yes, that is what it's called) that is not replaceable. Simply a spring loaded rod in a tube. It took me three times tearing down the carb to get this working freely, fixing the same indications. Nearly drove me back to drinking. :mrgreen:

No vacuum leaks, but I'm having trouble with getting a decent idle RPM without opening the closing the SCV. If you adjust the throttle cable and position too much it will close the SCV. I tried bumping the timing, but now it seems to be running too rich with too low of a standing idle.
Thanks on the power valve rods sticking, Explorer. It is moving freely so that is not the problem.

Bubba are you sure that there is no signal when you just rev the engine in idle? It's been a long time since my car had a LOM in it, but I thought I could rev it and get a signal to the dizzy while still in Park. I thought the LOM system basically picks a vacuum signal between the manifold and venturi, then "conditions" it and applies it to the dizzy...

I am getting a signal if I rev the engine. If I give the throttle a bump, I can watch the diaphragm on the SCV close on the carb (under the cage on the carb), and the timing is advancing on the damper at the same time.
It seems to have the flat spot, I reading about somewhere maybe between 2000 and 2500 RPMs, and bog out slightly.
Idle set around the factory spec at 600 or so RPM seems really low, and it just seems to be too low. It's running okay now, but wanting to die at lights with the low RPM.

One thing, I noticed when I had it running very good after the rebuild was that if I have it a little bit of choke when it was surging at about 2000 RPM, it would run smoother. I can't duplicate this now though. And that doesn't seem right as it would be closing the SCV during this procedure.

Surging can be caused by a lean condition. Look for vac leaks first. But with you using the choke to reduce the surging it sounds like the carb might be running lean too. Check float level and maybe its time for a rebuild?

If there is a vac signal to the dizzy off idle but the dizzy doesn't move then the dizzy vac can is probably leaking. It is a simple job to replace it.

I'm not sure if it is running too lean or too rich. When I pulled the #1 plug is was nice and clean and not wet. The exhaust is spitting and black like too rich a condition and it certainly smells too rich when it is warmed up. Very weird.

The distributor diaphragm appears to be working properly as if I pull the cap and do the "suck" test, it is advancing.

I'm sure you've checked other parts of the fuel system because you've done an 1100 rebuild - just a double ck (fuel filter, lines, pump, etc). Many of these 4W have often been run hard over their 30/40 yr history.

Pertonix is after mrkt? Boy, no help from me on that - just don't understand the ele end of it.