# Bad gas mileage

**URL:** <https://forums.speedlife.net/t/bad-gas-mileage/141805>\
**Category:** Canada Nissan Automotive\
**Created:** [March 12, 2006, 5:09pm UTC](https://forums.speedlife.net/t/bad-gas-mileage/141805 "2006-03-12T17:09:20Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![DeathBy240](https://avatars.discourse-cdn.com/v4/letter/d/258eb7/32.png) [@DeathBy240](https://forums.speedlife.net/u/DeathBy240)\
**Post date:** [March 12, 2006, 5:09pm UTC](https://forums.speedlife.net/t/bad-gas-mileage/141805/1 "2006-03-12T17:09:20Z")

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In my '85 Tercel, I am getting about 23 mpg when I should be getting about 30. I’ve replaced the air filter and fuel filter.Tires are inflated to the proper pressure. Spark plugs look good and so do the wires. I sprayed some carb cleaner in the carb and turned down the idle. What else should I try?

I guess I am losing backpressure as my muffler rusted off but I dont think that would cause that much of a loss in fuel efficiency.

When you turn down the idle on a carb does it reduce the A/F ratio throughout the power band or just at idle? I’m a newb to carbs.

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**Author:** ![Last\_Fuse](https://yyz2.discourse-cdn.com/flex034/user_avatar/forums.speedlife.net/last_fuse/32/5847_2.png) [@Last\_Fuse](https://forums.speedlife.net/u/Last_Fuse)\
**Post date:** [March 12, 2006, 5:43pm UTC](https://forums.speedlife.net/t/bad-gas-mileage/141805/2 "2006-03-12T17:43:22Z")

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Where have you been filling your gas up at and does she idle long? Also do you idle her out doors or indoors?

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**Author:** ![DeathBy240](https://avatars.discourse-cdn.com/v4/letter/d/258eb7/32.png) [@DeathBy240](https://forums.speedlife.net/u/DeathBy240)\
**Post date:** [March 12, 2006, 6:39pm UTC](https://forums.speedlife.net/t/bad-gas-mileage/141805/3 "2006-03-12T18:39:51Z")

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I fill up where ever is closest. No loyalty to gas stations for me. No, I dont let it idle long at all.

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**Author:** ![PyreXXX](https://avatars.discourse-cdn.com/v4/letter/p/bbe5ce/32.png) [@PyreXXX](https://forums.speedlife.net/u/PyreXXX)\
**Post date:** [March 12, 2006, 8:13pm UTC](https://forums.speedlife.net/t/bad-gas-mileage/141805/4 "2006-03-12T20:13:59Z")

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Dave, on a carb you’re going to have two adjustment screws.

1. The idle speed adjustment screw.

2. The fuel mixture screw. The backyard mechanic way to tune these carbs that I always read about is to lean out the car while it’s idling until it begins to stumble, then richen the mixture by 1/2 a turn of the screw. Try that - if someone richened the mixture to deal with crappy running problems because they didn’t change plugs/wires, etc., then that should help your fuel mileage.

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**Author:** ![DeathBy240](https://avatars.discourse-cdn.com/v4/letter/d/258eb7/32.png) [@DeathBy240](https://forums.speedlife.net/u/DeathBy240)\
**Post date:** [March 12, 2006, 8:53pm UTC](https://forums.speedlife.net/t/bad-gas-mileage/141805/5 "2006-03-12T20:53:29Z")

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Excellent! Thanks Kris, gonna try that tomorrow. Stupid non-fuel injected cars!

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**Author:** ![PyreXXX](https://avatars.discourse-cdn.com/v4/letter/p/bbe5ce/32.png) [@PyreXXX](https://forums.speedlife.net/u/PyreXXX)\
**Post date:** [March 12, 2006, 9:02pm UTC](https://forums.speedlife.net/t/bad-gas-mileage/141805/6 "2006-03-12T21:02:16Z")

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Meh, no computer to get in the way of the tuning. Try tuning a spec v, where the ECU starts ignoring inputs from the SAFC-II over time and just reverts to its stupid pig rich status.