Shocking MPG

hey guys
My rebuild is running great.
Shocking mpg though we are talking 8 to 9
all short trips and its pretty cold..
tires are aired up.I might have been getting that on my blowd up motor
You guys have any experience with the mileage getting better when they get broke in more..
I'm at a 100 miles or so
zero smoke of any color
does't miss
fires on 1st chug
havent put the HEI in yet
Brakes cant be draggin,,They dont work to good when you smash on um

 

Ive checked one on each side. both looked good. Break in is going good. getting used to the 420 is odd. thanks for the info though it runs so good I cant believe mileage is that bad..

I have an idea but i think its a new post so we will see..

 

a hundred miles doesnt seem like enough to get an acurate reading

 

thanks for the ray of hope

 

is you speedo reading right? running bigger tires than stock will turn odometer a little less. The brain trust here could probably figure it out for you if this is the case.

 

i usually get around 9-10 mph on my 225. t98-d18 w/od-4.88 gears. it runs a little rich but leaning it out makes it run poorly. rebuilt the motor about 10,000 miles ago. i was reading on the forum of guys getting 15-16! yikes

 

i'm getting 16-18 mpg, im' running a 420-3.73 gears and a stock gm 225 cam. it's also flat as a pool table around here. if you can get ahold of a g.p.s , check your odometer to see if it's accurate.

 

My old 64 CJ-6 with 5.38 gears and a Chevy 283 got around 14 mpg and that went up to around 16 with a Warn OD. Let it break in and it should improve. You'll notice better throttle response as the engine loosens up and the rings seat. Don't drive at a steady speed and load the rings by accelerating up a moderate grade in hi gear. That will really seat the rings.

 

Best I have gotten with my 231 is 18 mpg on a road trip to wheel near Tahoe. 4:88's, SM465 and an OD

 

color of the sparkplugs? When light brown and, preignition 8 degress. You have the best you can get with the carb you have. Try the CO emission?

 

In my experience, you'll see your best gas mileage when you use limited throttle and maintaine a steady speed........which is not what you should be doing really when you are breaking in an engine. Break it in properly and then check again.

 

When I bought my CJ5 with V6 in 66, I was dismayed at the gas mileage. I expected better after talking to others with that engine and rear ratio. It was about what your are getting and about what my 64 F head had been getting. After a few hundred miles and some new jets in the carburetor for higher altitude, things got much better. I got 18-20 mpg if I kept on the highway. If I went boondocking it dropped down, but it was still pretty good.

I think you'll see a great improvement when the engine is broken in.

John