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  #1  
Old 05-05-2008, 10:32 PM
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'72 250 M130 (Zeniths) - fuel economy question

I have previously posted all of the work I recently have completed on this car (rebuilt the engine and tore the carbs all the way down and cleaned them, etc). Had it running now for several months and the car runs great - cold start at the turn of the key, idles fine, accelerates smoothly with a lot of power and runs down the highway at 70 like a new car (maybe a little bit of an exaggeration here!).

Problem is gas mileage - noticeably worse than before. Also, I have hard, hot starts - have to crank for several seconds to get it to fire. I am getting 11-12 mpg around town, before it was 14-15 mpg. Haven't had it on the highway enough to test highway mpg. When I park the car in the garage, I can smell gas (for hours after I shut it off), but I can't find a leak, or seeping, anywhere.

I have had some trouble with the tranny flaring, but I think it is a linkage problem. Car will shift fine if I ease off the pedal some.

I know these cars never got great mileage, but shouldn't I expect better than 11 mpg? Can someone advise as to some 'likely culprits'?

Thanks, ryan

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Old 05-05-2008, 11:53 PM
t walgamuth's Avatar
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The mileage should get better as it breaks in. If the plugs look the right color for a good mixture I wouldn't worry about it too much.

Tom W
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..I also have a 427 Cobra replica with an aluminum chassis.
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Old 05-06-2008, 10:57 AM
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I would verify the float levels to ensure proper settings. The adjustments are made via copper washers of varying thickness; Use only one washer, and good luck locating them. Perhaps the Classic Center can assist. Another possible culprit is the fuel inlet valve itself. Also, check the fuel return valve to ensure it is not weeping from the sealing gaskets. Most kits seem to provide copper washers, but I have found them to be a source of leaks. My best luck was obtained by using fiber washers and re-tightening them after a few hundred miles.

Lastly, your hard starting may be due to heat valve flaps failing to operate properly. The thermo-springs available here are a bit still and tend to keep the valve in closed position far too long. If the valves do not move freely, this tight spring/sticky valve combo can over heat the manifold and carb which will cause hard hot starts. Use some heat valve lube, available from Chrysler dealers in an aerosol can...works wonders when used often.

230/8
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Old 05-06-2008, 11:20 AM
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Quote:
Originally Posted by rgnprof View Post

I have had some trouble with the tranny flaring, but I think it is a linkage problem. Car will shift fine if I ease off the pedal some.

Thanks, ryan
What exactly do you mean by "flaring"? My280S used to hold a gear longer than I thought optimal at times. I used to ease up on the pedal some at times to achieve silky smoothe upshifts whenever I wanted them. I just thought that was a charachteristic of these cars.

- Peter.
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  #5  
Old 05-06-2008, 12:37 PM
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I suspect the "flaring" issue is not really flaring, per se, but actually an issue of linkage adjustment that causes the transmission to remain in gear too long. Try shortening the adjustment slightly on the down link from the bell crank under the front of the manifold. I adjusted mine to book specification after some major work and the transmission remained in gear too long...the specification is for sea-level values of vacuum. The mechanical linkage and vacuum modulator are intended to work together for good shifts. If you are not at sea-level then the engine vacuum is lower and your adjustments need to compensate for this by reducing the influence of the mechanical linkage.

FYI, classic "flaring" occurs when the engine races up between shifts...for example, on the 2-3 shift the engine speed rises in the brief period between the release of second gear and the engagement of third gear. Precise internal adjustments are needed to ensure the release of one gear is quickly followed by the engagement of the next gear...but it is also essential to ensure the next gear is not engaged too early. This is a careful balancing act for transmission designers. Sometimes they deliberately have the next gear engage very slightly as the lower gear is releasing so there is a feeling of seamlessness or smoothness for the shifts.

The simple delay of the shift point, or artificially hard or soft shifts are usually always a matter of adjustments for the linkages or vacuum modulators.

230/8

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