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Why would it run better when low on fuel?

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Old 05-16-2013, 08:34 AM
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Why would it run better when low on fuel?

For the past couple of months, I've been noticing something very strange about my 8. It has noticeably more torque and idles better when I'm below 1/4 tank of gas. It's noticeable enough where I'll get in the car and once it's warm and I've been driving for a few minutes, I'll take off from a light driving like I normally do (shifting at 4-5k) and I'm like "Damn it's pulling hard today" and then I'll think to look at my gas gauge, and sure enough, it'll be below 1/4. It's not that it runs poorly the rest of the time, I can just tell a difference and it bugs me. Like enough to just drive around below 1/4 all the time

Any ideas? I'm thinking it could possibly be a weak fuel pump, but it should be the complete opposite scenario if that was the case....

I'm getting like 200 miles/tank city and 250-260 hwy. I premix 6-8oz/tank as well. It happens even if I don't premix though.
Old 05-16-2013, 08:41 AM
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less weight due to less fuel?
Old 05-16-2013, 08:55 AM
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Hi CJ,
I thought driving under 1/4 tank was risky.
I read about overheating fuel pumps, and fuel starvation on hi-G left turns.
Old 05-16-2013, 10:36 AM
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Originally Posted by paimon.soror
less weight due to less fuel?
Maybe...but it's a night and day difference. It doesn't run better at 1/2 than it does full. Just better below 1/4 period...

Originally Posted by BigCajun
Hi CJ,
I thought driving under 1/4 tank was risky.
I read about overheating fuel pumps, and fuel starvation on hi-G left turns.
Yeah, what you say is true. I don't have any issues though, quite the opposite haha.
Old 05-16-2013, 10:03 PM
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I would say it is leaning out a little more with less fuel and your picking up some of the pre mix from the bottom of the tank which did not mix well. not rx8 related but my weed wacker does the same thing when it is running low on fuel, it revs higher and just runs better.
Old 05-17-2013, 01:04 AM
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The 'Weedwacker Boost"!
I like it.
Old 05-17-2013, 01:19 AM
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Is that like Wacky Racers???
Old 05-17-2013, 04:00 AM
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Originally Posted by Stephen T
Is that like Wacky Racers???
2 stroke string grass trimmers.
Don't know what a wacky racer is.
Gotta get moving, have a good one.
Old 05-17-2013, 04:19 AM
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Originally Posted by BigCajun
2 stroke string grass trimmers.
Don't know what a wacky racer is.
Gotta get moving, have a good one.
When you get back from work you can read that I was gobsmacked as I always thought "Wacky Racers"was an American cartoon TV show. Did you have a deprived childhood or was I just incredibly infatuated by cartoons. Actually, probably the last thing!!
Old 05-17-2013, 06:40 AM
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Originally Posted by paimon.soror
less weight due to less fuel?
This answer

Originally Posted by Stephen T
When you get back from work you can read that I was gobsmacked as I always thought "Wacky Racers"was an American cartoon TV show. Did you have a deprived childhood or was I just incredibly infatuated by cartoons. Actually, probably the last thing!!
http://www.imdb.com/title/tt0122365/?ref_=sr_1
Oh yes, Saturday morning cartoons, good times.
Old 05-17-2013, 11:08 AM
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Originally Posted by aaronspeed
I would say it is leaning out a little more with less fuel and your picking up some of the pre mix from the bottom of the tank which did not mix well. not rx8 related but my weed wacker does the same thing when it is running low on fuel, it revs higher and just runs better.
This crossed my mind except that it does it when I don't pre-mix as well
Originally Posted by alnielsen
This answer

Wacky Races (TV Series 1968
Oh yes, Saturday morning cartoons, good times.
Pretty much the only logical answer I guess lol

Thanks everybody
Old 05-17-2013, 11:45 AM
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It leans out the fuel at higher loads. The engine goes crazy rich at some loads/rpms knocking everything down to around 12.5 max will add a very noticeable increase in power.
Old 05-17-2013, 01:49 PM
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Originally Posted by Harlan
It leans out the fuel at higher loads. The engine goes crazy rich at some loads/rpms knocking everything down to around 12.5 max will add a very noticeable increase in power.
Guess that's one of the ways a tune with the cobb can increase power (and probably mpg)

Man I want a cobb so bad haha
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