Fuel Mileage?

Latley my mileage has dropped to 13-17,i wonder what gives,its running good,spark plugs burning ok,could i have too wide a gap?

Well the duraspark box quit so I replaced it with an msd 6a and gapped the plugs at .60

Seems like 45-50 is what I've always heard with the MSD boxes, though I've steered clear of them due to some folks getting stranded with them.  I used 050 with my Crane fireball and HEI with no issues.

  On May 23rd you posted you were getting 21 mpg,  now you're down to 13-17???

Plug gap is way too much. More is not always better. .045 MAX, and I'm not so sure I'd go that high with THAT engine and status.
Highway driving will kill mileage. Anything over about 55 is it drops for most cars of that age - period.
If you drive around where the average is say 45, you'll get a lot better. Approach 55 and it might stay stable or rise a bit, but get over that, and it drops. Over 65 and it REALLY drops, fast.
Don't take my word for it - ask your old science teachers, study the studies that have been done for decades.
And finally, you can't base MPG on a single tank. I keep a spreadsheet and enter my info at each fill. I go by the running average, or the average of the last 2 or 3 tanks. I consider (and make note of in the spreadsheet) the WEATHER, was it cold, or  cool? Hot? Dry or humid? My Eagle really thrives when the morning temps are cool (50s) and the air is just a bit humid. I can even feel the difference.
I also noted, and this is weird, that at one station I fill at, when I get gas there the car just "seems" more peppy (yeah, real scientific, but I get so in-tune with what I drive it's almost like an extension of me...... people "like me" get that way) and I note an increase in MPG - just with the gas from that station compared to the others.
the reason I say you can't go by a single tank is that you can't tell me or convince me that you fill the car to the EXACT SAME level of fuel in the tank EVERY TIME and you are never a gallon or so off from the last fill. You don't have a sight-glass, and even if you did, that's a large surface area and a 1/4 inch difference this fill from last is quite a bit of fuel. So you need to AVERAGE them. A single tank doesn't mean squat, IMO. I pretty much ignore it when folks say "this tank was....." unless you are keeping very accurate records, always fill at the same pump, parked the same distance from the pump and facing the exact same direction each time, and get it filled to the exact same level as the last fill.
Otherwise, I think you are just jousting windmills.

In my case, I have all the receipts, I keep a spreadsheet, make notes of the weather and driving conditions, what sort of driving I did for each tank full, in-town, or highway, trip or short commutes, and let the spreadsheet average things out for me. I do see a rise as the engine breaks in.
And I can note changes in MPG based a lot on weather conditions and driving for that tank.

(there is still no spot on that poll for my car, which is now typically mid-20s)


Edited by billd - Jun/18/2012 at 8:07am