14 mpg guzzler

John Fox · Post by **John Fox** » Thu Jul 27, 2006 12:22 pm

My 78 spider seems to be running fine but its mileage took a nosedive after a mechanic dropped in a replacement carb. It's now down to under 14 miles per gallon (about half what it should be).

I'm no mechanic but I've tried adjusting the fuel mixture according instructions in my Haynes manual, without any luck. The manual also refers to a fast idle adjustment, but I can't for the life of me find the screw on my Weber carb. When I get the engine to 2500 rpm and push the little fast idle button, then release the throttle, the rpms stay unchanged.

I'm at a loss. Any advice would be greatly appreciated.

So Cal Mark · Post by **So Cal Mark** » Thu Jul 27, 2006 1:00 pm

first you need to make sure the carb is working properly; choke opens completely, float is set right, no fuel leaks. If all of that is okay, the carb probably needs to be jetted properly. Adjusting the fuel mixture will have neglible effect on fuel mileage, unless all you do is idle all day.

TVST*R · Post by **TVST*R** » Thu Jul 27, 2006 10:40 pm

I only get about 16.3 mpg...I assumed this was average.
Of course I have a bad ass header,exhaust, carb....
T

So Cal Mark · Post by **So Cal Mark** » Thu Jul 27, 2006 10:48 pm

AND a heavy foot?

TVST*R · Post by **TVST*R** » Fri Jul 28, 2006 12:34 am

Well, there is this particular musical exhaust note that I only
hear at around 4k rpm...and well, I listen to alot of music.
Just wait til I add the cams!

Spyderbuddy · Post by **Spyderbuddy** » Fri Jul 28, 2006 6:45 pm

i still get about 25mph and i let her sing between 4000 and 4500 down the highway you do the math 226.3 miles to 9.256 gallons

Spyderbuddy · Post by **Spyderbuddy** » Fri Jul 28, 2006 6:47 pm

previous fill up was 250.01 miles and 10.109 gallons

TVST*R · Post by **TVST*R** » Fri Jul 28, 2006 9:35 pm

Nice! Is you engine stock?
T

Spyderbuddy · Post by **Spyderbuddy** » Fri Jul 28, 2006 10:10 pm

very 1981 124 spyder 2l fuel injection

So Cal Mark · Post by **So Cal Mark** » Fri Jul 28, 2006 11:39 pm

oh yeah, the FI cars are much more efficient than a carb

Noaki · Post by **Noaki** » Sat Jul 29, 2006 7:11 pm

My 1982 FI is getting about 13 MPG highway, but I got somewhere round 35 driving city the other day. So either something is really funky, or my gas gauge is going out. I'm going to be replacing some sensors soon, so maybe that'll fix things up.

Spyderbuddy · Post by **Spyderbuddy** » Sun Jul 30, 2006 8:03 am

cold start valve if it sticks open your mile per gallon will go down

Noaki · Post by **Noaki** » Sun Jul 30, 2006 1:03 pm

My cold valve doesn't work at all right now. Heven't fixed it because it's usually in the high 90s or low 100s around here

TVST*R · Post by **TVST*R** » Mon Jul 31, 2006 4:49 pm

TVST*R wrote:I only get about 16.3 mpg...I assumed this was average.
Of course I have a bad ass header,exhaust, carb....
T

Just filled up..I'm now getting 19 mpg!!!!
WoW! Nice!
We finally got 'er dialed in I think with the smaller
idle jet!
Thanks Mark.
T

So Cal Mark · Post by **So Cal Mark** » Mon Jul 31, 2006 6:54 pm

cool! 3 mpg improvement is great