Calif. smog failure.....
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Junior User
Joined: Feb 2003
Posts: 98
Likes: 1
Calif. smog failure.....
Took my 79 F-250 4WD plow truck (400M 2bbl Motorcraft carb) for a smog test yesterday and it failed miserably at idle. Allowable max for HC 250, mine 278. CO 2.0, mine 5.78. Turns out the mixture screws were WAY too rich. After 3 tweaks and retests (no charge for a retest, and no report to DMV 'till it passes) it passed at HC 11 and CO 0.00. Ended up about 2 1/2 turns out instead of 5. Better than most new cars. So....I be smiling!!!!! Idle was kinda lumpy so I gave it 1/2 turn richer when I got home and all is well.
Elder User
Joined: Nov 2004
Posts: 517
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I have the 2bbl on my 77 w/351m, whats the best way to get the right mixture? I've got it set by warming the engine then turning each one in until it get rough and then back it out until it smooths out again, is that right?
Moderator
Joined: Aug 2002
Posts: 6,104
Likes: 384
From: Southern California
In general, after you obtain the highest smooth idle speed, back out (lean) the mixture screws until the idle just starts to fall (about 1/8 + rotation) and should put you pretty close, retard the timing by 1 degree, let the idle be about 50-100 rpm slow from the mid range setting, pull the air filter.....dump a gallon of methanol into the tank and it will pass with flying colors
