Small Block Chevy does NOT like the Cold.
 

I rebuilt the small block chevy not too long ago to put in my truck. Pistons, rings, bearings, cam, valves, ignition, and a quadrajet rebuilt by Cliff.
Ever since it has gotten cold, it feels and sounds like a mis-fire until it warms up all the way. I pulled the plugs and they're OK, if a little rich, but still ok. At cold start-up I can hear a mis-fire out of time bang,clank, in the passenger side long tube header, but then after it warms up, it goes away and sounds fine. Any ideas where what to check? I'm thinking maybe ignition wires need to be sorted a little less tangled? It's only on that one side.

I'd think exhaust leak or an intake manifold leak- without being being there to hear it myself.

Retorque everything.

Check it out in the dark around plug wires and look for arcingSmileWavy

cool, thanks, good ideas to start

If your wires were arching you would most likely have the problem all of the time. What type of choke is on the car? It might not be adjusted properly. Did you check the choke before starting the car when it is cold and make sure it is actually closing all of the way?

that popping is air getting into the system somewhere...

Lean misfire perhaps since the engine is still cold. Does it pop back through the carb? Carbureted engines don't run well until they are warmed up. Fuel injection has spoiled us.

For sure. I used to have to sit in my El Camino freezing my butt off trying to get it warm enough to idle when it was really cold. I converted to throttle body FI many years ago and never look back. It fires up in a second when it is zero or 110. It is the best upgrade on that car ever. Equal adding the Griffith's AC system on the 911 as the best upgrade ever and having a car I can drive in the heat.

The quadrajet is and always was a piece of crap.

We always called them Quadrajunk.

Describe your cold start procedure. What does it take to get the truck to start when it is cold?

Pump the pedal all the way to the floor 3 or 4 times B4 turning the key. Make sure choke is adjusted properly. Cold engines require more fuel. Ur not getting it.

I have some cars that miss on cold startup, I attribute it to plugs being wet from either condensate, coolant, or fuel Since it doesn't persist I haven't figured it out totally. I suspect it's water because when it quits missing I immediately see more steam out the exhaust.

So, I'll try richening the idle mixture on that side. I remember leaning them both a while ago.

Cold start procedure, three or four stomps to set the choke , then it fires right up in just a few cranks !

Sounds like someone opened one up as a novice expecting to find a parts count similar to that of a Holley and instead found a far more complex fuel delivery apparatus. Undeterred, disassembly of this marvel of fuel atomization continued until they were so hopelessly in over their heads that they threw the entire lot of parts in the trash and jumped on the "Quadrajunk" bandwagon. Shame, because if they'd taken the time to really learn about them they'd have discovered that the Quadrajet is probably the finest street-use carburetor ever designed.

SmileWavy
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Thanks Norm, that's what I was thinkin

And if yours was built by Ruggles my guess is that it's not the cause of your recent difficulties. He's not perfect, mind you, but there's a pretty good reason you have to get in line if you want him to rebuild your Quadrajet.

Good luck!

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Was thinking exhaust leak that seals off after heat expansion at first blush. I have owned a car with a cracked exhaust manifold that made boatloads of noise until warm then ran (sounded) like a sewing machine. Mine only sounded bad - it did not "feel" like a miss.

Carbureted intake manifold leak could create a miss-fire or weak-fire at a specific cylinder. Given heat that is in the 200F (intake) vs 500F (exhaust) range I am not seeing 200F heat sealing off an intake leak (intake to head) that is big enough to create a noticeable miss. Just talking. OP could always try the carb/brake cleaner spray test.

I have no argument.

Cliff Ruggles has the world's biggest backlog. I'm thinking of Sean Miller for my next QJet. I've got a 750DP that works fine on my pontiac, but still the idea of a Q-jet for part throttle is appealing. I just can't get the damn Q jet to quit being so finicky about fuel pressure. I need to upgrade my delivery system.

Today's tip from the 50's:

You're doing it wrong. Cast iron Chevy exhaust manifolds aren't meant to have gaskets. iron-to-iron only.Throw away the silver Fel-Pro gaskets that burn out all the time.

me like the Q-jets.
anyways, once upon a time, i had an open chamber big block with a tunnel ram, wouldn't idle worth ****.
we threw on an msd ignition module, and it would fire right up and idle like a champ. some serious spark action there.

Excellent post.

I could not agree more!! I was fortunate enough to be schooled by a much older GM tech ( at the time) taught me all the tricks on those. BTW - there are many different versions / part #'s. Makes a huge difference to have one at least close in zip code to the application its sitting on.

Further - there were actually 800 CFM versions that only came OE with certain hipo Pontiac / Buick / Olds. Those are the ones to use in performance street engines larger than 400 CID.

I believe there was over 10k versions over the years. Many people have screwed them up by mixing and matching pieces.

Cadillac's also had large CFM Q-jets.