Miss - No Load Driving & Reversing

[LuvNLife]

I need some help brainstorming a problem, rather than tossing random parts at it.

'85 C10, with a new Chevy 350/260 long block. At idle, it's smooth as can be. Drop it in gear, same. Accelerate lightly, and I begin to hear a random miss; don't really feel it bucking or anything, I just hear it. Driving steady state at like 25 mph, same. Pull out on a main road, throttle response is fantastic, half pedal and it pulls great, with no hint of a miss. At steady cruise, 55-60 mph, runs and sounds great. So long as there's a load, like a small hill, it sounds great. When I drop it in reverse to back up my 150' inclined driveway is the worst. Not only do I hear the miss, I feel it bucking. The truck also smells pretty rich at idle, but zero black smoke.

Here's the hardware I have: engine with less than 200 miles on it, Edelbrock Performer EPS intake, 1/2" wood carb spacer, Edelbrock AVS II 650 (no choke) carb, fuel pressure regulator set to 4 pounds, Patriot shorty headers, 10mm new plug wires, R45TS plugs, new (inexpensive) HEI connected (now) to ported vacuum, valves lashed to 1/4 turn past stopping of "clacking". The trans is a Turbo 350 with about an 1800 stall converter (was in the truck already).

Thoughts and recommendations would be appreciated.

 

[gotyourgoat]

Has it been like this from the beginning or it took 200 miles to appear?

 

[LuvNLife]

OK; good to be back. First, the dog got sick; she got better. Then, the wife got sick (not Covid); she got better. Then, I dropped a brake rotor on my middle finger; good enough to type again, but ugly to look at.

First thing I did was go out one night and fire up the engine with the lights off to look for any arcing; nothing at all. Physically checked the plug wires for cracks, breaks, etc., and nothing. Then, I disconnected and plugged the vacuum advance. Fired the truck up, took it for a drive, and it runs out great. No missing no-load or loaded going up 2-3% grades. Backing up my drive, no bucking, no missing whatever. The only difference I noticed was the exhaust was a bit louder, but that may be the mufflers breaking in (Smithy glasspacks).

So, taking a shot in the dark, I'm guessing something is extremely wrong with the vacuum advance in the distributor. I've used 4 of these inexpensive HEI's in other engines, and never had a minute's trouble, so I guess I was overdue. For now, I'm just going to leave it plugged off, since there's no other issues with running hot, etc.

Thanks for everyone's input.

 

[LuvNLife]

Has it been like this from the beginning or it took 200 miles to appear?

The guy that did the engine install for me had all of the rockers adjusted way too tight when I picked it up, and it idled really bad. That told me despite his years of wrenching on SBC's, he didn't know crap. Took it to another shop where the guy and his father both have real-world experience with performance SBC's (racing cars and boats), and he adjusted the valves properly, and set the timing to 10 degrees. That's when the no-load miss showed up, and the hideous bucking in reverse. That shop only did exactly what I told them to, so he didn't troubleshoot it.