Technical Holley backfiring, stumble

You can pull the distributor and move it over one tooth to get it back in to adjustable range.

 

Adjust the coil bracket.

 

LOL I was doing this in the 80s when I made dirt and gas was just 'expensive'. Now I make an OK dime and gas is 'ridiculous'. Not much changed, eh?

I was able to devote some time to the Chevy today. Started by marking the timing mark on the balancer again, and made two marks a few inches before and after. Helped me find it. With the dial-back light set at 34, timing mark was right on 0*. So then I advanced timing to the max vacuum I could manage: 14" Hg. Steady needle. Brought rpms down to 1,000 again, four cornered again. Max mercury is 14" with all four turned out about 3/4 turn. Bringing it back down to 1,000 rpm, 13". Steady needle. Sprayed start fluid around the carb base gives no rpm increase. Cleaned carb with carb spray cleaner as well for yuks. It was a little gunky.

Took it for a drive. Throttle was more responsive. On a rev match downshift there was no stumble now. At a light on a hill I had no idea I was doing it until the rear end started stepping out, but I was easily breaking the tires lose at about 2 grand in first, without trying.

I made a couple of stabs to WOT. No backfire. Great. On my way home, just coming off idle from a red light, BLAM! . I was gently leaving the line.

I fattened up the idle mixture a touch, took another drive. Same result. No backfire at a quick trip to WOT but I did get a big one while coming off a stop. Mechanical tach, I'm not sure of the exact rpm. Might have been 2K might have a bit higher might have been lower. Definitely not a WOT issue in that situation.

I can't play with it any more, the last two hours was all I can do today. I'd love to swap out the plugs right now as that can be the problem, but I need to so yard work before it rains and it was either go to the store come back and R+R plugs, or play with timing and test drive. I chose time and drive, because well, I got to drive it and now I'm not so worried about the dist. being in wrong. Baby steps...hoping the plugs are the last puzzle piece but I also think the idle screwes were tightened too much in their seats in the past.

 

True, and I can also remotely mount it but I'm resisting that until it is necessary. There's a cover that is supposed to go over it, and retarding the timing doesn't seem to be the answer now anyway. But thanks.

 

No need to pull the distributor, just retard it and move the plug wires around one spot.

 

That sounds like cheating. So I like how you think.

 

So the moment you've all been waiting for and already knew:

I had a chance to get into the garage after work. I have carbon fouled plugs. I'm slightly surprised by the plugs. Not surprised re: the condition, it was running very rich for who knows how long, stunk like gas in the garage before I worked on the carb a bit. Hope fully this is the last bit of my puzzle on the engine. I'm making a separate thread about the plugs in case it helps somebody else.