Or better said, will the EXHAUST be cleaner with more or less timing advance? I'm mostly refering to idle/cruise conditions, not WOT.

I'm going to be recurving my distributor soon and would like to know what provides cleaner exhaust at idle/cruise, more or less timing?

Looking at factory specs, I'm guessing its believe that less timing burns better, since most smog era cars have low timing advance settings.

Right now I have about 18 degrees of intial and it starts and idles fine but it was stinky even with the 600cfm carb, moreso with the 780cfm.

It would be nice to have a curve that burns cleaner than the current one.

Thanks,
Enrique.

Less timing will give a cleaner burn, especially at idle. That is why they tend to use ported vacuum on emission era cars.

Mike

Thanks, I'll give it a try.

Define "cleaner". What reduces HC and CO generally increases the NOx. What decreases NOx will tend to increase the others.

I would expect that retarded timing would produce less NOx. It might increase the HC and/or the CO.

I expect that the retarded timing will make the exhaust manifolds run hotter at idle. Which is fine if you have an air pump, it will keep the mixture burning in the manifolds which then reduces the HC and CO.

Are you asking because you need to pass some emissions test? Or are you just trying to get rid of the "stinky" smell? Generally, the stinking and eye-burning exhaust is a result of HC and CO, not NOx. Are you too rich at idle?

I would seem to think that a custom curved igintion with the recommended specs, AND a properly tuned carb with yeild the best all around results. It has to be a combo of both! Having said that, 10 -12 degrees intial with 36 total in by 3000 RPM and a finely tuned curb idle and main circuit would do the trick. This will also most likely deliver the best fuel economy and that helps with the price of gas. :D

I'm asking because it stinks, this car doesn't need to be emissions tested, unless the law changes again.

I think it is running too rich, but I tried everything with the 600cfm carb and it was still stinky. Of course, I made it even worse with the bigger carb but it sure runs better on the track.

Maybe I should turn the idle screw in some more and re-adjust the speed with the throttle blade position. I think that would provide more air and less fuel?

Are you opening up the throttle blades into the transition slot? That will often make for a rich idle and stinky. What carb are we talking about here? What is the idle vacuum?

Holley 3310-3

I don't think its into the transfer slots, but the funny thing about this carb (and other holleys, from a search I ran on here) is that one of the slots is slightly longer than the other one.

The part I don't understand about the blade/slot configuration is that if you have the blades nice and low (just barely exposing the slots) the idle drops really low and the way I raise the idle back up is to give it more advance. My starter has no trouble kicking over even with a bunch of advance. Maybe I should close down the throttle as far as possible and just add more timing? Would that work better?

I know I could just drop the 600cfm back on but for some reason this near-stock engine loves the 780cfm carb, even more when the secondaries come in quicker.

If it likes the 780 and you like the 780 then make the 780 work.

What is your idle vacuum?

I'll check the vacuum tomorrow. I know it was 20ish with the 600cfm.

Enrique, you want the front blades relatively square. Yes, it may lower your idle, but you can bring that up by slighly opening up the secondaries by turning that PIA screw in the baseplate, or by tinkering w/distributor. Its not a big deal to have to turn your idle screw a little open to get the idle where you need to...just not alot!!! Try manifold vacuum - that will gain you a bunch of idle rpm (down on the baseplate).

Square off your transfer ports, and start the car. Take note of how much you need to turn the idle screw to get the idle where you need it. Then do what you can to get the egine idle speed up so you can back the screw out to where it was or close to. That will immensly clean-up your rich idle. Been there done that. Transfer slot adjustment will not help w/cruise though b/c you then have your throttle open. Try to run the mixture screws in as far as you can untill the engine doesn't like it - that will clean-up your idle and cruise.

BTW, I think all our motors will stink a little to some degree, they are performance motors and there is not cat converters. I has a 85 TA that I took the cat off and you couldn't stand anywhere neart that car after that. And that was an emission car!

we used to drill a hole in each of the primary blades it lets you idle with the blades almost closed eliminating the xfr slot problems