Mpg?

[Rescue Diver]

I took my Holley 670 truck avenger off two weeks ago to go back to my Edelbrock 600 cfm 1405 carb. I have a full blown tune kit for that carb so I wanted to mess around with it. The holley allready had the heaviest spring on it for the secondaries but the best I could manage was 10-12MPG. The Edelbrock bumped me up to 13.9mpg for one tank and then 12.5 on my second tank but I drove it harder the second time. I want to see what I get with just the primaries since they are smaller more like a Qjet spreadbore. If I can get 14mpg and then switch to a 5 speed in my Scrambler to bump me up some more then I will be fine with that. When I hit the trails I can hook up the secondaries for the horsepower and more fun times. I understand what you say about the carb sizes. I am pretty decent at tuning them but it takes time and patience to get it right.

Sounds like you've got the right carb for it.

What's your total ignition timing set at? If you can bring on a little more mechanical advance in the mid range RPMs without it pinging, you'll bring up your MPG. Incorrect timing(not enough advance) can easily cost you several miles per gallon.

Mine went up noticably when I re-tuned my advance a couple weeks ago.

 

[Kane]

Sounds like you've got the right carb for it.

What's your total ignition timing set at? If you can bring on a little more mechanical advance in the mid range RPMs without it pinging, you'll bring up your MPG. Incorrect timing(not enough advance) can easily cost you several miles per gallon.

Mine went up noticably when I re-tuned my advance a couple weeks ago.

I have an MSD billet distibuter and I set the advance fairly aggressive. MSD includes springs and stop tabs to do a custom curve. I set it for the most aggressive curve and took the Jeep for a drive on the highway. I heard it ping so I took one spring off and went one size thicker then installed one size bigger stop tab for the total mechanical advance. I have about 36 degrees mechanical advance coming in around 2300 RPMs. My highway cruise RPM is 2600. I have got away with more advance on the Holley but it was tuned richer than this one. My initial idle timing is actually conservative to help keep my idle at 800 RPM's but it does ramp up pretty quickly. I tell you what for as long as I have had this motor I think I haven't stopped tinkering with timing and carbs. I allways expect some magic to happen.