Mongo50

Greetings all. Question for you. I have a 331 stuffed into a 73 ford courier. I have been nursing it back to health slowly but surely but I just failed emissions. It has 68 heads, calling for .035 plug gap on an 86 roller block, which ran on heads with plugs gapped at .044. I am leaning to gapping the new ones at .035 since thats what the heads call for but I dont know how, or even if, plug gap effects emission. 8.7 /1 compression ration. MSD dist, box and coil, with an Edelbrock intake and carb. Whatcha think?

67mustang302

It will. What did it fail on? If HC content was high then you need to lean the tune out. Carbureted I'm assuming? If it runs poorly as you lean it out you may need a larger plug gap. And just as an fyi, newer emissions controlled vehicles run plug gaps as large as .060 in order to ignite the leaner mixtures.

Derf00

If it's an interference motor, run it at .035, if not, then try 0.044 first and then 0.035 and see if it runs differently.

Derf00

Is 73 considered smogable? I thought only 77 and newer required smog in AZ?

Mongo50

Thank you for the replies, yeah this year, anything newer than 1967 needs to be tested. The CO was way low and the CO and HC both were ok at speed, I just failed HC at idle, which is all they really test at. If you fail the first idle, then you run up to speed to clean it out a little and then another test at idle. I was at 440 and 400 is the limit. I had leaned the idle circuit out the way I always have. Turn each screw in until you can hear the engine dropping a little, then back it out a quarter turn. Sound right? Whats an interference motor? And if im reading you right, then you want a bigger gap for a leaner idle mixture? The intermediate and main jets in the carb are fixed. thanks for the help!!

67mustang302

I'd run the idle as lean as you can. And how the hell can they smog anything from the 60's with a sniffer? There weren't any standards for them in the first place. Carburetors produce HC at idle, it's the nature of how they operate. Just trying leaning it a bit more, and maybe add a few degrees timing.

Mongo50

OK< will do. thanks for all the help!!!

JPJP

Retard the timing for cleaner emissions.

Also, since you have the MSD ignition you can open up that plug gap (closer to .060") say, maybe .055" gap...to take full advantage of the unit as mentioned earlier.