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**WorkinLonghorn** · 02-08-2017, 01:53 AM

Engine size? Freeway/City driving percentages?

Do you find soot in the tailpipe?

Did you check to see if the vacuum advance diaphragm is broken leaving you to drive around with the timing retarded 15 degrees or more?

Your tires are inflated to the proper pressure?

Just the rear end was switched to 3.73??????

Did you put a vacuum gauge on manifold and check this?

Did you check the engine compression with a warm engine, throttle wide open (all plugs removed)?

What about the smog system (if any), is the egr working, is the air pump still installed (if it had one)?

02-08-2017, 01:53 AM	#5
WorkinLonghorn Senior Member Join Date: Dec 2006 Location: Studio City, Calif. Posts: 2,857	Re: 78 K20 Gas Milage Suggestions Engine size? Freeway/City driving percentages? Do you find soot in the tailpipe? Did you check to see if the vacuum advance diaphragm is broken leaving you to drive around with the timing retarded 15 degrees or more? Your tires are inflated to the proper pressure? Just the rear end was switched to 3.73?????? Did you put a vacuum gauge on manifold and check this? Did you check the engine compression with a warm engine, throttle wide open (all plugs removed)? What about the smog system (if any), is the egr working, is the air pump still installed (if it had one)? __________________ '69 GMC C2500 Custom Camper, 8 1/2' bed, New GM 350, NP 435 Close Ratio 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, 2nd owner, Work-Truck supreme. Best $300 I ever spent. Last edited by WorkinLonghorn; 02-08-2017 at 01:59 AM.