Author Topic: idle mixture screws  (Read 4697 times)

Offline 3GOATS

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idle mixture screws
« on: April 15, 2009, 12:16:51 PM »
Newbie Question on idle screws. After rebuilding carb how many turns out would you start with?
Which one is which? air/ fuel?
This is on a stock quadrajet for a 80 chev 350. 17080215.
Rebuilt the carb following cliffs book and it runs exellent. I returned the idle screws to where they were before rebuilding and so far ok. . I guess I got lucky.
The book doesn't mention how to initially set mixture. Unless I missed something?
Thanks

Offline Cliff Ruggles

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Re: idle mixture screws
« Reply #1 on: April 15, 2009, 05:39:55 PM »
How far out depends on the year of the unit, and what modifications, if any were done to the engine, and to the caburetor?

The 1979 and later units used fine pitch threads, so each turn moves the mixture screws less distance than pre-79 models.  The holes under the mixtures were also smaller on later units, and the tips of the needles had long tapers.

Basically, we recomend apprx 3.5 turns out from seated for all units, then fine tune after the carb is placed in service for best idle quality at the leanest setting(s).   Some 1979 and newer units with small holes under the mixtures screw will need to be closer to 4.5 turns out from seated for initial run-in......Cliff