The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post

68 TT · 06-06-2010, 10:53 AM

You really need a vacuum gauge to adjust the mixture screws properly. Set one screw for max vacuum then back it off until it starts to drop, then adjust the other the same way. Once you have done them both go back and do it again. The setting of the second screw will throw off the first a little.

After that is done set your timing to factory specs (unless you have a bigger cam) then adjust your idle screw to get the desired idle speed. Don't forget to disconnect and plug the vacuum advance hose when you set the base timing.

If the mixture screws don't alter the vacuum then the passages behind them are gummed up and it needs cleaned out better.

06-06-2010, 10:53 AM	#14
68 TT Still plays with trucks Join Date: Jul 2009 Location: Spokane, WA Posts: 3,563	Re: How Do I adjust the... You really need a vacuum gauge to adjust the mixture screws properly. Set one screw for max vacuum then back it off until it starts to drop, then adjust the other the same way. Once you have done them both go back and do it again. The setting of the second screw will throw off the first a little. After that is done set your timing to factory specs (unless you have a bigger cam) then adjust your idle screw to get the desired idle speed. Don't forget to disconnect and plug the vacuum advance hose when you set the base timing. If the mixture screws don't alter the vacuum then the passages behind them are gummed up and it needs cleaned out better. __________________ miSSed opportunity - ground up creation of an AWD 1994 454 SS that never was http://67-72chevytrucks.com/vboard/s...d.php?t=795577 69 C10 shortbed stepside 400 small block - built like what a super sport truck could have been 69 K20 lwb TBI 350 4L60E NP208 14-bolt Dana-44 w/disc 68 Camaro SS / RS 500hp 439 inch roller cam big block 4L80E 79 Malibu TPI 350 4L60 w/ Z28 steering & sway bars