Whats up with my gas mileage?

[Quik8slvr]

1054813

when i first put in my 350 i was getting between 12 and 15 mpg on average, then it blew up, so i purchased a newly remanufactured long block, and now im getting 8-9 mpg on average but everything is exactly the same except its a different block and different heads, although still a stock 350 block and heads...am i running to rich? im new to carb's since the old 2.5L was fuel injected, is there a way to adjust the carb so i dont use soo much gas, i know its possible for the 350 to get better then 8 mpg, thats why it is so frustrating to me! :-x

Quik[addsig]

 

[jay89]

1054814

I don't know what part of the country your in but up here in the north east between October and March there is an additive they put in the fuel for emissions that drastically reduce your mileage?[addsig]

 

[Quik8slvr]

1054830

this has only been 3 weeks ago when i was getting 12-15, all thats changed is the engine[addsig]

 

[Jeepr89]

1054860

Were the camshafts and heads the same on the two different motors??? My friend put a GM350 in his 80 Malibu last year and he only gets about 8mpg??? [addsig]

 

[Tug-n-pull]

1054865

I love my 4 banger! :-D sorry you are haveing these problems. Is the new motor still in the break in period? I am no wrench but I am trying to help! tug[addsig]

 

[Quik8slvr]

1054888

The new long block is completely 100% Stock, its a 1969-1977 350 with 2 bolt mains, the old block was completely stock, except it had a Crane cam, and it was 4 bolt main...thats the only difference between the two engines, the new engine is still breaking in but i didnt think you'd get worse gas mileage during break in, do i need to tune my carb? could it be running to rich?

Quik[addsig]

 

[dingus]

1054907

just glancing through my haynes manual... its' citing the following reasons for poor gas mileage:

-air filter clogged
-ignition timing off
-incorrect idle speed
-low tire pressure
-fuel leakage
-choke not operating properly
-dirty or clogged carb jets/fuel injectors[addsig]

 

[JP]

1054909

you mentioned a crane cam in the older motor, my experience is that if you swap a cam, you need to fiddle with the carb to match the profile of the cam. If you swapped the carb from the old motor... start tuning!![addsig]

 

[carriss]

1054992

check your air filter if it's dirty not enough air is coming though [addsig]