25 MPG One Week, 18 The Next (Still No Luck)

[Durania]

The week before I had intake gasket failure my brat got 25 MPG give or take and thats all city driving. I did the gaskets and now I am getting 18 miles per gallon, what gives?! It has been cold (low 20's) and the only thing I can think of is it idling with the choke on at about 2800 RPM's for about 20 minutes. Would that affect my gas mileage that much?

[joostvdw]

is this an SPFI engine?

 

if so, the ECU has been adjusting the mixture for the vacuum leak you had before, at the moment, it's injecting the same amount of fuel as before the vacuum leak, so, its running rich, thus explaining the decrease in mpg. Unplug the battery for a while (+- 1 hour) this will reset the ECU.

 

if it's carb, dunno, maybe someone rejetted the carb to cope with the vacuum leak? I know nothing of carbs...

[Durania]

This is a weber.

[joostvdw]

mmm, oke, only thing I can think of is that the jetting you currently have is too big and when you had the vacuum leak it evened it out to a nice mixture.

 

oh, and, when you changed the gasket, you obviously removed the intake and perhaps the carb, check the fuel lines and filter for small cracks, they may be leaking

[Durania]

I dont know what it could be, I checked all my hoses and everything today to make sure they were all hooked up. Could the weather have that much of an effect on it?

[Virrdog]

Where in Tennessee is getting that cold?

 

But yeah, idling a carb engine for a long time can definitely affect your mileage. You probably won't be able to find out your real mileage until next spring, when you stop the extra idling and they stop pumping the crap winter gas.

[Durania]

Where in Tennessee is getting that cold?

I live on the Cumberland Plateau, its been getting down into the upper 20's high 30's these past few days.

 

Thanks for the advice on mileage, at $3.00/gallon its hard on people.

[Durania]

Been monitoring the mileage the past few weeks, managed to get 22 and that is strictly highway miles, thought it had finally corrected itself since I lowered the choke idle speed about 1000 RPMs. Still no luck, would I turning the idle mixture all the way to lean and then come back up a bit maybe help some?

[Durania]

Bump

[Subaru_dude]

I guess the only thing you can really do is just start messing with the carb. Maybe add some additives to the gas?

[Durania]

Finally got around to fixing the mixture on my weber today. Cross-referenced with the redline weber page and went out and put the mixture back to where it should be. I had to turn the screw about 4 1/2 turns to get it back to where it bottoms out . Put it at 2 turns and compensated the idle speed and drove it to work. I have yet to tell a difference just yet but really hope that I have this thing worked out. The only goofy thing I have gotten is that every so often, it will rev about 500 RPMs up then back down by itself, I don't get this.

 

http://www.redlineweber.com/html/Tech/carburetor_set_up_and_lean_best_.htm