Running hi-test will net you more miles per dollar. This goes hand in hand with the timing, but you'll need to use up the lo-test (if that's what's in there now) before you can really take advantage of it. Using it, you may get up as high as Jim's 10°BTDC, but 8° is not uncommon. This also reduces temps.
Make sure your carb air intake is drawing from in front of the radiator where the air is cooler and denser.
This one might sound a bit strange, but I try to slow down a bit in headwinds and actually speed up in tailwinds to improve mileage. The resistance increases with the square of the airspeed.
Get some air in those tires. Running them at the stated max for the tire/wheel will get you better mileage, but you may find the ride a bit harsh. I run mine well above the minimums stated in the charts.
We just got back from a trip to Colorado. We have a 31' with a 454 tbi, headers, dual exhaust, and OD transmission. We averaged 7.84 mpg for the whole trip, cruising speed was about 70 mph with the dash AC and genny/roof AC running nearly the whole time, we were not towing anything.
1993 Coachmen Catalina 31'
Chevy P30, 454 TBI, Hedman Hedders w/ x-pipe and Jones Full Boar mufflers. Same mileage as stock exhaust, but we get there faster!
Looking for a better rig...
There are many different versions of the Q-jet. One big thing is where the power valve starts to kick in. It is vacuum operated. As the vacuum drops, the mixture is enriched. If that enrichment is set too aggressive, you may be running in mixture enrichment at cruise. That will kill the mileage. To start with, of course do a full tuneup. Then buy a vacuum gauge. This will help you monitor where the vacuum is at cruise. Then you can compare that to how the power valve is set up and possibly change it to something more suited to your application.
Lets reverse some of this proceedure stuff Daveinet, Most of the Quads off the shelf come with 11 inches of vacuum springs which means once your vacuum reaches that 11 inch point your "Power rods" start dumping fuel for more power....
I pulled the clock out of the dash (2/18 is the size) and installed a nice vacuum gauge (2 inch increments) which is easy to see...
NOW you can find out by driving around where your vacuum range is, For me idle is 19" (depending on the weather) cruising down the flat level slab at 62 MPH (no wind) it runs 14"--17" but never close to the stock 11" spring dumping.
Now for the hill climbs....Small hills BUT long the vacuum drops to 9"-11" which on your stock carbs will be needlessly dumping fuel, You see I have the STOCK SPRING in mine which opens up at 6" and I do go below 6" at times.....
See folk's you gotta know where your at so you have the correct direction to head into.....
I have suggested that all of you carb folk's simply visit a good carb site (Cliff Ruggles) and look at some of the goodies offered...
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