318 CARTER CARB REPLACEMENT

[furyman]

i recently failed our local smog test(air care),it seems my 52 year old carb is not up to there standards!the car runs excellent with it on but it has high emissions @ idle,no matter how much we adjust the idle circuit, the car still runs to rich to pass.my thought was to replace the carb with a newer emissions friendly version so i borrowed a friends edelbrock 1406 performer 600 cfm carb thinking it would be a bolt on proposition.(replacing the carter 4bbl exisiting carb on the vehicle now).not so!the carb inlet where the air cleaner fits is different but more importantly the newer edlebrock card is not a true square bore carb(having slightly larger secondary's).the result is the the rear throttle plates touch the intake manifold runners.solution's?would the holley 1815 be a better fit?i would like to stay away from carb adaptor plates or grinding the top of the intake if @ all possible.i would probably install the original carb back on after passing the smog test.i would like to keep the car as original as possible.thanks in advance for the input.

[RICKYMOPAR]

Furyman; I am sure if the throttle shafts are not worn out you could clean and rebuild your original AFB carburetor. I am sure you need to clean and install new needle and seats then adjust the float settings. These early Carter AFB carburetors are less problematic than the new Edelbrock carbs and require no modifcation to work. in short...Dirty idle circuits and float problems cause high emission readings. The old AFB will be able to pass emission testing and be adjustable on the idle circuit.

[Matthew Keij]

And Ricky here is the carb doctor. He really knows his rungs about carbs.
He is the best!

[big m]

An important thing to consider when you say it failed the smog test, is what were the HC [hydrocarbon] and CO [carbon monoxide] readings?

High CO and high HC readings together is a sign of an overly rich air/fuel mixture. Low CO and high HC is usually indicative of an overly lean air/fuel mixture, and can also be caused by a vacuum leak.

If the Hydrocarbon reading is sky high, yet the CO is within parameters, an ignition misfire, fouled spark plug, burnt valve or other problems could be the cause.

There are generally two tests done in a typical smog test, idling, and 2500 RPM readings. These are typical of west coast tests, and they may be different elsewhere.

---John

[Denver 59 Fin Convert]

John F. has a solid point. Can you scan and post the Emmission report so we can see what area's it was high in. This is a great learning opportunity.

Rebuild the carb or refresh the ignition parts or a combination of both to get the passing grade of a well run motor (albeit to 1959 standards or better)

John Q.

[RICKYMOPAR]

True, Carbon monoxide adjustments usually inexpensive, some high hydrocarbon repairs can be very expensive. The question was 318 carb replacement?

[furyman]

thanks for the relys guys.i will post a smog report on the site for you to view,in the next day or so(i,ve been away for a few days).thanks for the input.
mel
the engine is a recent rebuild so should be in proper condition,the carb is the original with no history of a rebuild,the car actually runs great except for the one high reading,it passed the other 5 categories of the smog test.

[furyman]

here is the smog report i received on the fury.as you can see,all passed except the hc @ idle,passed hc on driving test,thoughts?

[RICKYMOPAR]

Too lean, Engine fully warmed up, air filter in place. Check the timing, vacuum advance line disconected and pluged. then rehook vacuum advance.and Hook up a tachometer and adjust Idle mixture needles equally to best idle 'highest RPM reading' and then turn them back in 1/8 turn. Too much advance timing can cause high HC readings.

[big m]

Ricky nailed it-
Too lean, either mixture adjustment or vacuum leak, or your initial timing is too far advanced.

---John

[furyman]

thanks for the input guys,i now think i,m heading in the right direction.(i need to pass the smog test in order to get my collector plate (READ CHEAP INSURANCE).
my problem is that the car runs so dam good that it is hard to reconize that there is a problem.
mel