| [GMCnet] MPG [message #271727] |
Wed, 11 February 2015 18:49  |
Len Novak
Messages: 676
Registered: February 2004
Location: Las Vegas, NV
Karma: -3
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Senior Member |
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Quick question.....
We have a coach that went a whopping 100 miles and burned about 23 gal of
gas.
Empty coach, had not been driven or started in 5 years.
Suggestions? I'm a bit lost for words here.
Cheers,
Len and Pat Novak
1978 GMC Kingsley
The Beast II with dash lights that work and labels you can see!
Fallbrook, CA new email: B52Rule@Roadrunner.Com
http://www.gmcmhphotos.com/photos/showgallery.php?cat=4375
www.bdub.net/novak/
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Len and Pat Novak
1978 GMC Kingsley
The Beast II with dash lights that work and labels you can see!
Las Vegas, NV new email: B52sRule@Gmail.com
http://www.gmcmhphotos.com/photos/showgallery.php?cat=4375
www.bdub.net/novak/
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| Re: [GMCnet] MPG [message #271730 is a reply to message #271727] |
Wed, 11 February 2015 19:08  |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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Len Novak wrote on Wed, 11 February 2015 16:49Quick question.....
We have a coach that went a whopping 100 miles and burned about 23 gal of
gas.
Empty coach, had not been driven or started in 5 years.
Suggestions? I'm a bit lost for words here.
www.bdub.net/novak/
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Len,
A little of 4 miles to the gallon is certainly not real good. However, it doesn't mean it is a bad engine. In fact, after sitting that long, the old girl did pretty good... she started and ran and drove.
1. Were any of the wheels hot from dragging brakes?
2. I would pull the plugs and see how they look. Maybe blackish meaning the carb is leaking gas.
3. Timing could be retarded... did it run warm. That is an indication of retardation.
4. Maybe timing is OK but the weights on the distributor are stuck. That will make a huge difference.
5. Is it missing? Plugs, wires, etc. Might look at it run in the dark. I have seen plug wires put on quite a show
6. Is it a 73-74. If so and if it has been converted to HEI, check the voltage at the little conning tower that lays on the side. The old distributor had a resistor wire that lowered the voltage to the coil. HEI likes a straight shot of battery.
7. When the plugs are out might as well check the compression.
Hope this helps.
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
[Updated on: Wed, 11 February 2015 19:09] Report message to a moderator |
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| Re: [GMCnet] MPG [message #271740 is a reply to message #271727] |
Wed, 11 February 2015 19:44 |
Tilerpep
Messages: 404
Registered: June 2013
Location: Raleigh, NC
Karma: 7
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Senior Member |
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I had you beat my first road trip - I figured I got 3 mpg! I put fifty bucks in. Half hour later my wife says "how's it doing on gas?" I replied "I think it has nearly used it all!" Within three minutes it started to sputter. I wisely threw the aux tank switch - to discover that didn't work. AAA first and only call came next.
I rebuilt the carb (twice) on the trip and it went up to 5 mpg. Reset timing when I got home and that took it to 7 or 8. Since 8 is the bottom end of "normal", I may not do any better than that. My PO put a different cam and gears, and I found out after my last few long runs that my front calipers were having issues. I have two AC's and a large storage pod on top, an awning, and wind wings on the front windows, so it's not like my profile is exactly "sleek". My goal is 10. Tire pressure, brake drag, timing are good to check. There was a posting recently about reduced voltage coming through the key/ignition cylinder to the coil, similar to what George mentioned. I still have to check if I am getting full voltage at the HEI.
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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| Re: [GMCnet] MPG [message #271742 is a reply to message #271727] |
Wed, 11 February 2015 20:13 |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
Karma: 5
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Senior Member |
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I have been there. I think 7mpg is easily attainable. Anything less you have fixable issues. That is a conservative number. Mine took a proper carb rebuild and tune up to double the gas mileage.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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| Re: [GMCnet] MPG [message #271753 is a reply to message #271751] |
Wed, 11 February 2015 21:06 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Senior Member |
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Check your choke. If it is partially closed you will be running rich and using an excessive amount of gas. We had a guy come from El Paso to a Saguaro Jetset rally a few years ago who's coach quit on him along I-10. He had the coach towed to Benson where they replaced the battery and determined the coach was out of gas. Steve Ferguson took a look at it when they got it to the campground and found the choke stuck most of the way closed. That explained, at least in part, the horrible gas mileage he was getting on the trip.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: [GMCnet] MPG [message #271776 is a reply to message #271727] |
Thu, 12 February 2015 05:56 |
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SeanKidd
Messages: 747
Registered: June 2012
Location: Northern Neck Virginia
Karma: 4
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Senior Member |
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The easiest thing to check is your fill line rubbers, underway, fuel is sloshing back and forth between tanks, a leaking elbow or coupling may not be noticeable at rest, and would account for your paultry performance...check the onan feed line too.
Sean and Stephanie
73 Ex-CanyonLands 26' #317 "Oliver"
Hubler 1-Ton, Quad-Bags, Rear Disc, Reaction Arms, P.Huber TBs, 3.70:1 LSD Honda 6500 inverter gen.
Colonial Travelers
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| Re: [GMCnet] MPG [message #271831 is a reply to message #271780] |
Thu, 12 February 2015 16:44 |
Terrasmak
Messages: 40
Registered: December 2014
Location: Las Vegas
Karma: 0
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Bill Freeman wrote on Thu, 12 February 2015 07:27If it has the stock Quadrajet carburetor try the following suggestion. Check that the power piston on the primary side of the carb is not stuck. You can feel it with a small standard screwdriver inserted down thru the vent tube on the carburetor. There is a spring that pushes the piston up and it can stick in that up position if the engine has not been run for a long time. This piston controls the primary side metering rods and it will run very rich if it is stuck in the up position.
Going to check this on my way to work .
Len Novak, 76 Eleganza II, Las Vegas
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