ok i took my car through inspection yesterday and it did better than expected. i have a 383 with rpm intake 750 performer carb, and hollowed cat. and no smog pump. i passed the the high side of the two speed idle test where it has to be revved to 2500rpm but i failed the low side at idle. the hydro carbon limit is 220 ppm and mine was 846 ppm. and the co% limit is 1.20 and mine was 3.07 my question is can this setup be made to pass and what will get me there? how close will just a new cat me to passing or will it alone do the trick? also will the carb need some adjusting?

my high rpm results were hc 180 and the co% was .61 both have the same limits as above.

any help would be appreciated i am trying to fix this myself if i can my only problem is i dont have access to a sniffer. i have a back up plan if i cant fix.

 

ttt

 

Your high HC and CO at idle indicate overrich idle AFR and incomplete combustion.

Less idle static timing improves HC at idle. (raises exhaust temp to burn more HC off in the exhaust) {but kills the throttle response}
The high CO indicates a high idle AFR. lean the idle down. (larger idle air bleed, smaller IFR and or more idle bypass air. {"idle eze" and or PCV bleed}{ the easy way to temp-tweek the idle circuit for the test}
Make sure the motor is all warmed up when adjusting the idle mix screws as the manifold plenum temp plays a big part in how well the fuel vapourzes in the manifold at idle.
Liquid fuel does not burn, passes right thru the motor into the exhaust shows up as high HC (incomplete combustion) More manifold heat improves idle fuel vapourization allowing a "leaner" idle screw adjsustment to get the best idle quality. Small idle screw adjustment makes a big difference in the HC reading even when it doesn't seem to change the idle speed. The point of maximum idle manifold vacuum (best idle) will not create the lowest HC reading. Slightly leaner will. A bit too lean and it will missfire at idle and HC will skyrocket again.
Thats why the OEM's went to feedback carbs and hot water temps and heated air inlet temps.

High performance cam timing (duration and overlap) causes severe exhaust delution and fuel pass thru at idle, further creating high HC. (thats why a race cammed motor idles so rough and needs tons of idle timing) Higher idle speed and loose valve lash (less effective valve overlap) will help.
You should be able to reduce the HC a good bit at idle by dialing in the CO {low CO indicates correct AFR at idle"
From that point nice hot working cats will burn the rest off. Cats work best when the AFR is correct {low CO} Leaning out the idle will lower the CO
Retarding the idle timing will Lower the HC.
A hot motor (high water temp thermostat) helps too.
More engine heat increases fuel vapourization quality allowing leaner/cleaner idle.

What cam is in this motor?
The edelbrock performer 750 is calibrated way to fat/rich in the idle circuit to pass a smog test. Do you have another carb to go with for the test? Like a Qjet or a VS holley.
Leaning down the cruise calibration of the eddy carb may help (primary jets and metering rods. And creating a adjustable idle air bypass in the PCV hose) Aquarium pep **** bleed T'd into the PCV hose.

 

i have a melling .480/.480 lift 230* duration @.50 i have my old carb from my 305 which passed emission just fine but that also had all the smog hooked up to which is not on the 383. so can i just put the old stock carb on and cat and go or would i have to adjust timing. also if i put the old carb on do go back stock timing?

 

ya that cam is going to make getting thru the emissions a bit of a challenge.
The cool sounding idle is exactly what is causeing the high idle HC and CO.
You're going to have to try things based on what I layed out for you.
Yes you will have to monkey with the timing to get the best result.
You will need a functional cat @ minimum. The Q jet should work better than the performer. It will need to be monkeyed with too. But is leaner to start with.
Worst come to worst you'll have to pull the cam and install a milder one that has less overlap and duration.
Something like this http://store.summitracing.com/partde...3&autoview=sku gets much better emissions numbers ( with correct carb tune and timing) and most of the power of your 230/230.480" cam
I'm in the same boat here with my 406SBC. Sails thru the cruise portion but has high HC and CO at idle using the same edelbrock carb and a even bigger camshaft.. It is definatly fatter than it needs to be at idle.