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Question for the Mileage Experts
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Author:  cackle [ Mon Feb 02, 2009 4:50 pm ]
Post subject:  Question for the Mileage Experts
Image First off, thanks for a great website, I have a question about mileage on my slanty. Ive installed a 1968 engine from a Dart in a 1950 GMC truck without windshield(planning installing glass). It has a Holley one barrel with an electronic breakerless ignition. Currently Im getting 8-10 mpg. It starts quickly, does not miss, plugs are white, timing at 12 degrees ,truck weighs 3080lbs. Could the cab missing windsield create that much drag? Could the t.v. cable out of adjustment be the cause?(it shifts normally). The rear end is a 9in ford out of a 1964 truck with 2:90 ratio. Thanks in advance.
Author:  Reed [ Mon Feb 02, 2009 4:54 pm ]
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I doubt it. With careful tuning I was able to get my brother's 1983 Dodge Shorty van powered by a slant six to get 21 MPG on the highway. I would suspect you need to check for vacuum leaks, rebuild the carb, and recurve the distributor to match your application. What kind of transmission are you running?
Author:  cackle [ Mon Feb 02, 2009 5:01 pm ]
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Im running the original transmision that came in the Dart...904?
Author:  THOR [ Mon Feb 02, 2009 5:01 pm ]
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Do you know the history of the engine you got? I know that when I bought my '71 Dart, the timing chain was junk, but advancing the timing and slapping a better carb on there almost masked the problem. One way to easily tell is to grab a vacuum gauge, and put it on the engine. If the engine is in good shape, you should be pulling close to 20" if not more of vacuum @ idle while not in gear, and around 16-18" while in gear @ idle.

Note that these numbers are for a stock engine as well.

My '71 was pulling all of 10" while cruising at 30 mph, and pulled 15" at idle in neutral. I also got 8-10 mpg. It ran absolutely fine other than the crummy mileage. Remember that running too lean will also cause poor fuel economy as well.

Might be something worth looking into.

Awesome rig you got there!

~THOR~
Author:  GENT [ Mon Feb 02, 2009 5:05 pm ]
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Plugs are white? They should be a nice light brown to tan color.
Author:  cackle [ Mon Feb 02, 2009 5:12 pm ]
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The man I bought the engine from had removed it in order to install a v8 and showed me the reciepts of the little old lady who had surprising imaculate maintenance records. The slant had 40,000 miles at the last oil change. I bought the engine and trans for $600. The plugs are white with black at the end of the treads.
Author:  oklahoma joe [ Mon Feb 02, 2009 5:20 pm ]
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you may want to see if your brakes are draging or something else is causing extra rolling resistance. I had a truck one time that had old flexible lines and the crimped connectors rusted and swelled and keeped residual line pressure on the caliper pistons. Does the car seem to roll easy or does it slow as soon as you take your foot off the gas?

Joe
Author:  cackle [ Mon Feb 02, 2009 5:27 pm ]
Post subject: 
Quote:
you may want to see if your brakes are draging or something else is causing extra rolling resistance. I had a truck one time that had old flexible lines and the crimped connectors rusted and swelled and keeped residual line pressure on the caliper pistons. Does the car seem to roll easy or does it slow as soon as you take your foot off the gas?

Joe
Truck rolls easy, brand new brakes, power booster, front discs. The exhausts seems to produce alot of black soot, I dont know if it is because of the upright exhaust. No black smoke.
Author:  SlantSixDan [ Mon Feb 02, 2009 11:21 pm ]
Post subject: 
Welcome on the board. You're running rich - probably because of faults in the Holley 1920 carb that cannot be addressed with an ordinary carb rebuild kit. The float is probably saturated (therefore heavy), and there's very likely one or more check balls AWOL from the metering block. Do you have spare carburetors to play with?
Author:  440_Magnum [ Tue Feb 03, 2009 9:14 am ]
Post subject: 
Quote:
The exhausts seems to produce alot of black soot, I dont know if it is because of the upright exhaust. No black smoke.
Can you clarify that? What do you mean "a lot of black soot" but "no black smoke?" The inside of the exhaust pipe being coated with black is pretty normal for a carbureted engine on today's unleaded fuel. Visible smoke is not normal.


One other thing to consider: is your odometer accurate with the rear axle ratio end and the size tires you are running? If the odometer is reading too low, that would also fool you into thinking you're getting really bad mileage.
Author:  Reed [ Tue Feb 03, 2009 11:13 am ]
Post subject: 
You might be interested in reading what I did to my brother's van to get the gas mileage I did. See here
Author:  cackle [ Tue Feb 03, 2009 5:17 pm ]
Post subject: 
Quote:
Quote:
The exhausts seems to produce alot of black soot, I dont know if it is because of the upright exhaust. No black smoke.
Can you clarify that? What do you mean "a lot of black soot" but "no black smoke?" The inside of the exhaust pipe being coated with black is pretty normal for a carbureted engine on today's unleaded fuel. Visible smoke is not normal.


One other thing to consider: is your odometer accurate with the rear axle ratio end and the size tires you are running? If the odometer is reading too low, that would also fool you into thinking you're getting really bad mileage.
I made an upright exhaust with a rain cap that exits behind the driver and up about 2in above the roof, and the soot is water and black carbon, I believe is because I have not drilled a vent hole for the water to come out of at the bottom. Im in the process of getting a hold of a gps to verify my speedo as you suggested, Thanks.
Author:  ESP47 [ Wed Feb 04, 2009 9:26 pm ]
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Listen to what Dan said, I bet you anything that one of the seats that hold the check ball in popped out and you've just got fuel flowing through the metering block causing your rich running condition (bad mileage) and black carbon coming from the tail pipe. Just pop the cover off, remove the float and see if theres a little ball rolling around inside of there. If there is then you can try and re seat the ring and ball back in there and see if that helps. Chances are it wont seat properly and you're going to have to replace the metering block or get another carb.
Author:  THOR [ Wed Feb 04, 2009 10:46 pm ]
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If you end up wanting to try a different metering block for a 1920, let me know, I have some spares. :)

~THOR~
Author:  cackle [ Thu Feb 05, 2009 5:05 pm ]
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Thanks for the help, I soon as I can I will take a look at the carb.
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