I finally got my engine running and driving great after the rebuild. I put a comp cam in, got a valve job done and milled the head .050. I got an Offy 4 bbl manifold and a Holley 390 on it. The engine runs GREAT but I only get low 15s on the highway. This is my daily driver to school(about 45 miles every day). The carb has #50 primary jets(I live 7,000ft above sea level), 6.5 power valve, purple secondary spring, and an orange/pink accelerator cam. Its a little discolored so i cant tell. Timing is 5-10 btdc at idle. I run mid-grade at the pump. Any suggestions will help.

Do a distributor recurve to get better mileage.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Did it get good mileage, or better, before the carb upgrade? If so, then the carb fuel metering is too rich. You need to get the power valve timed to the correct vacuum level for your engine.

Ted is correct about timing though. If it did not get good mileage before, then timing is likely not ideal. You want about 50 total, with high vacuum, max centrifigal, and initial added together. Good timing can make a world of difference. Also check the condition of your basic wiring. If you are losing voltage between your alternator and your ballast resistor you are losing power at the ignition, and thus economy will be poor. Fix is to clean or replace terminals or replace wires as well.

Sam

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The setup i had before was a Holley 2300 500cfm on the stock manifold. This was before the rebuild and so it got about 12 mpg. Which wasn't too bad for a stretched timing chain. And today in my auto class I will check all the connections and put a voltmeter on the coil.

What vehicle, and what tranny and rear?

Sam

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Its a 71 dart with an a904 and the 7.25 rear

[quote]The carb has #50 primary jets(I live 7,000ft above sea level), 6.5 power valve, purple secondary spring, and an orange/pink accelerator cam.[/quote]

High altitude requires smaller main jetting, and perhaps smaller accelerator shot. Reason is, you have less oxygen up there, so to keep mixture as close to stoichiometric you have to add less fuel to the thin air.
See Holley’s[url=http://www.holley.com/data/Products/Technical/199R8108-2rev2.pdf] instructions for jetting above sea level[/url] on page 10, “Main Jetsâ€￾. line # 3. Also be sure idle mixture is not too rich, tune with vacuum gage and sniffing exhaust at idle to tell when it stops stinking or in other words too rich.

Look [url=http://holleytv.com/?cat=13]here[/url] for other tuning tips.

I run an old Holley 390 with out of the box 512 jets at sea level, engine has over sized valves, big cam, CR 9.5:1, 3.55:1 rear gear, stiffer yellow secondary spring, and 904. I get 18.5 mpg on the open road at 55 to 65 mph. In town at low rpm, mpg numbers ain’t so hot.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

My guess is your rear has a 2.76 ratio, (or something close to that). You should get better mileage than you are. Explore the options listed so far. I think with good tuning you should get 18-22 MPG.

Sam

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18-23 mpg is what im shooting for but a lot of my driving Is up hill and high elevation So I can understand a little mpg drop. Colorado is not the best place for engines.

I checked the voltage on the coil while the engine was running and the meter read <2 volts. What is it suppose to read? And if It should be 12 volts what needs to be checked? Also I saw in Clifford performance to run size 48 jets with the Holley 390 and a 8.5 PV. And the secondaries are not opening up at all with the purple spring, would that affect millage? You would think that just running on two barrels would get better millage.

Are you running electronic ignition? HEI? If you've got a ballast resistor check the voltage there. Should be higher than 2 as far as I know.

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1968 Plymouth Barracuda [Daily Driver]
1972 Dodge Dart Swinger [Lent out as Daily Driver to a friend]
2010 Challenger R/T 6 Speed

No im running stock single point distributor and i do not have a resister as far as I know.