Rough engine 1966 c20

[elliotweiland]

I just finished rewiring my c20 and fired it up for the first time since purchase. I installed a new distributor, coil, fuel filter, air cleaner, harmonic balancer, put fresh high grade oil, topped off the radiator, put new valve cover gaskets and rebuilt the stock 2bbl rochester. The truck idles quite high, maybe around 1500 rpms give or take (haven't hooked up the tach). I know that the exhaust is just about **** but I'm wondering if it could play this large of a role in the poor idle. I have fixed exhaust leaks on a few other cars and its made quite a bit of difference so I guess that might be it. Inside the cab there is a bang sound. Low and muffled but doesn't sound like a knock. I'd guess the exhaust has a lot to do with that. My question is what are all of the possible culprits that factor into this rough and high idle. Brakes aren't hooked up so I can't say how it runs at speed. Thanks for any help

[TJ's Chevy]

High idle indicates an air leak somewhere....air leaks will be the cause of poor idle and rough running. Not to dis you in anyway...but poor carb tuning can also be a factor..only mention it because I'm not entirely sure on how deep you went though the carb...Speaking from experience...my 292 used to have the ol Model B rochester on it...rebuilt it once...major air leak somewhere...would stall all the time...but idled fine...test ran...top speed of 50 mph...second rebuild...went deeper in the carb...accelerator pump was shot...replaced it....ran a heck of alot better...still had a small air leak...acceleration greatly improved and top speed of 80( took awhile to get there)....and the air leak still present ended up being a vacuum leak through the accelerator linkage.....Since then I have changed manifolds and bolted on headers and put on a 4 barrel....no air leaks here. lol So I'd check for air leaks.

[MikeN]

Too much timing will make it idle high, as will an incorrectly adjusted choke.

[elliotweiland]

Thanks for the help tj, it is definitely a possibility as I wouldn't doubt the tuning is not perfect. I do plan to get a quality set of long tube headers and a full pipe and muffler. I also would like to upgrade the carb and intake at some point.
Mike, what do you mean by too much timing? What adjustment do you think I should make?

[wildearp]

It is also a good idea to pull the plugs. You may have a couple oil fouled. Sometimes they do this because of valve seals. I had it happen and changed plugs. It hasn't happened since. Don't put it off, just pull them and check.

[elliotweiland]

I replaced all of the plugs and made sure to gap them properly. Thanks for the advice!