'79 K10 400 won't start w/ new alternator and battery

[chargrove217]

Hey gang! Looking for some advice:

Background: Truck is a 79 K10 SWB, TH 400 tranny, 400 crate motor that has around 40k on it. It has an edelbrock carburetor in it.

Truck was running like a beauty until a few weeks ago my wife was driving it and it just died while running. I'd been a little dubious about the battery as it had felt a little weak now that it's gotten cold. It wouldn't even crank. I put the battery on a charger till full charge, put it back in the truck, and at that point it tried to start but wouldn't catch. I figured the battery was just caput so I just got a new one. It did the same thing. At this point I'm thinking the alternator, so this afternoon I just put a new alternator on it (I figured for the cost, a new alt was worth the peace of mind anyway). It still won't start, it cranks strong and occasionally sounds like it tries to fire. There is fuel in the line to the carb, and when I released a little pressure on the fuel line at the carb it squirted a little fuel so it doesn't seem like getting fuel is a problem. Since it tries to fire once in a while I don't see why it wouldn't be getting spark. But at this point I've reached the end of my limited knowledge!

Any advice on the next thing to try to troubleshoot? I did fiddle with the adjustment knobs on the carb a while back, but it was running really solid after that. I have always noticed it's just a little sluggish when you hit the gas. Not like a lack of power, more like a little bit of delay between when you hit the gas and it responds.

Hopefully I've given enough info to be helpful! Any help is greatly appreciated!

PS: I'm largely a mechanic noob, this truck is a long-term project and I'm trying to learn!

[bd]

Was fuel added to the tank shortly before symptoms developed?

Since the engine cranks strong, give the fusible links at the starter and the firewall junction block a stout tug to see if any stretch or separate.  Inspect them to make sure none bear signs of soot or heat damage.  Check the wires that run from the starter through the 1" steel conduit at the back corner of the block and up behind the engine to the firewall junction block and bulkhead connector for any evidence of heat damage from close proximity to the exhaust or chafing to ground on sharp edges.  If any of the fusible links are damaged, make sure that none of the wires from the starter have been inadvertently pinched between the starter and engine block or between the transmission bell housing and engine block during a prior repair.

Don't make the mistake of assuming the spark is good until you verify it by testing.  Use a test light to check for ignition voltage at the distributor cap "BAT" terminal while an assistant cranks the engine.  Disconnect a wire from one of the more accessible spark plugs, slide the insulation boot up the wire to bare the metal terminal and have an assistant crank the engine while you check for a strong blue-white spark.  Be sure to maintain >6" between your hand and the bare terminal of the wire so that you don't get a nasty shock.  The spark produced by HEI should jump a ~3/4" air gap with little trouble, fairly consistently.  Grab the distributor assembly and make sure it is tight and doesn't rotate in the block.

[hatzie]

The HEI Ignition system can give you a pretty good jolt if you're not careful.  The old wives' tale in the 80's was it was a bad idea to run the HEI system with a plug disconnected even for test. 
I have a Lisle inline spark tester I bought in 1988 for $4  It's up to $11 now.   I don't believe the old tale but IMHO it's well worth it to not get walloped by 50,000 volts from the ignition coil.  It gave me a heckuva headache the last time I got nailed by one.

If it died right after a fillup and you're in the frozen North pouring a bottle of isopropyl drygas in the tank and dragging it into a heated garage may cure it.  Frozen fuel tanks/lines aren't as common with E10 & E15 fuel as they were when these trucks were new but it still occasionally happens.

[chargrove217]

Thanks for the leads! I have a spark tester on the way and I will check out all that other stuff. Fortunately it's not a daily driver!