Emissions Test

72bluNblu said
Now that makes more sense!

It boggles my mind a bit why an engine that heavily modified is being tested to a factory 1973 emission standard, but whatever.

The idle will have to be leaned out a ton, and it will need to run HOT. The double pumper likely isn’t helping, even at idle.

It’s not gonna like it. Lean on the mixture, retarded on the timing and about ready to overheat.

Not horribly? It’s more than doubling the hydrocarbon output of a factory 1973 engine. ‘73 was still pre-cat and all that other garbage, that’s a pretty high HC count to begin with.

Now having the engine specs it makes sense, that thing is probably close to double the horsepower from a factory 340 in ‘73, so moving twice as much air and fuel too. Shouldn’t be that rich, but idle isn’t where that engine is happy.

I say not horrible because I've seen a stuck injector cause a reading over 10k. A friend had a car with a kjetronic that was slightly out, and read 3600. We adjusted idle mix from 12.3 to 13.7 and it cleaned up to under 400.

For a cammed small block, 900 isn't that bad IMO. It'll need leaned way out, but it'll probably run there. I'd try it with a nominal idle timing. Too much advance will push up the nox, not enough will increase CO.
I don't see a nox reading, so I might be inclined to keep it at 20 and just lean to max rpm, then lower the idle as much as it can be while happy. I'd also make sure the pcv is good and maybe even cheat by letting it suck clean air...