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Posted By Discussion Topic: Gas hog -- page: 1 2     51f1 09-25-2015 @ 2:01 PM reply profile send p.m. Senior Posts: 573 Joined: Oct 2009 I have a '51 F-1 with an 8RT and the higher ratio rear end. I get about 13 mpg. The engine was rebored .030 over and has a NOS carb that I put a kit in. The engine has about 5,000 miles on it, but even before I restored the truck, I got 13 mpg. Richard supereal 09-24-2015 @ 2:43 PM reply profile send p.m. Senior Posts: 6819 Joined: Oct 2009 Also check for one or more dragging brakes. It is common for the aluminum pistons in the wheel cylinders to corrode and stick with old fluid in the system. Be sure that the air cleaner element is not clogged, and the muffler isn't loaded with carbon, etc. Be sure the thermostats are both working by pulling them and testing with a pan of water and a candy thermometer on the stove. All of these can affect gas mileage, as can front end alignment and correct tire pressure. From your description, it looks as if you have covered the carb, timing, etc Driving an old truck above 60 with the original rear axle gearing is probably always going to eat gas. 40cpe 09-22-2015 @ 9:30 AM reply profile send p.m. Member Posts: 477 Joined: Jan 2010 The utility body is extra weight, and tools added. I don't think you are too far off what can be expected. You can play with the point that the power valve kicks in until the power drops off to an unacceptable level. I hope you can find a solution. This message was edited by 40cpe on 9-22-15 @ 9:31 AM carcrazy 09-21-2015 @ 3:27 PM reply profile send p.m. Senior Posts: 1691 Joined: Oct 2009 You might want to install a vacuum gauge so you can monitor the engine vacuum while you are driving the vehicle. With higher overall gearing and increased weight you may be operating the engine under a higher than optimum load which will cause the engine to labor at lower vacuum levels. The lower vacuum will cause the power valve to open and the spark advance to decrease. TomO 09-21-2015 @ 8:54 AM reply profile send p.m. Senior Posts: 7271 Joined: Oct 2009 If your plugs are showing a rich condition, the power valve could be the problem. If they are not showing a rich mixture, I would leave the carburetor alone. The timing of the power valve opening has more to do with performance than mileage. The power valve will stay closed until the vacuum drops to the value that the power valve is calibrated to. The difference in mileage between opening at 7.5 inches of vacuum or 5.5 inches of vacuum is hard to measure. At steady throttle the vacuum should be above the opening point of any power valves sold in kits for the Holley carb for Fords. No 51 jets are the recommended size for the 8RT-9510 carburetor for your truck. Tom agriffey 09-20-2015 @ 10:34 PM reply profile send p.m. Member Posts: 28 Joined: Sep 2015 Oh, and the front end. It had a 1/4 inch toe-out. I changed it to almost straight ahead with slight toe in. didn't seem to affect anything. It should be zero with radial tires. I carry 35 lbs. pressure in the rear and 30 in front. My tool load is usually around 400 lbs. unless I have an engine or engine hoist loaded in the back. agriffey 09-20-2015 @ 10:25 PM reply profile send p.m. Member Posts: 28 Joined: Sep 2015 The truck had maybe 3,000 miles on the engine rebuild when I bought it. Maybe more, probably less. I Pulled the engine to change the chattering clutch and adjust the valves. The valves were all '015". I put them .013" intake and about .018" exhaust, best I recollect, It was in 2005 I think. I also took the pistons out. I cleaned the crud off them that was causing it to seize up and not start from old gas. It sat 6 years only being moved to get My T speedster out maybe 6 times a year. Big mistake. I have been driving it daily about 4 months. Never drove it the first 16 years I had it. It had a 3.92:1 rear end , I installed a 3.5. I put all new brakes on it, the do not drake or make any sound when I spin a wheel. I used the 15 inch wheels from the F100 I took the rear end from. It has 235 R15 tires on the rear. The overall ratio is still better than original. I avoid commute traffic, and don't worry about the mileage if I do get stuck in it. Yesterday I drove from Hayward to Livermore. 23 miles each way, 55 MPH all the way, both ways. Went at 11AM, came back at 3 PM. Driving habits? I got 20 with my 3.0 Aerostar 5 speed, same load of tools. I got 25 to 26 with my Toyota pickup. same load, and it had a carb. I get 37 when I drive my wife's 2001 Corolla. I used my '84 Volvo 244 about a year for work. I got 27 MPG on longer freeway hauls, 25 average. I drive my old Ford like I want it to last. I keep plenty of distance behind traffic as I have stock brakes. I keep the go-pedal pretty steady. I need to check the power valve. It could be wrong. The previous owner liked to go through those Ford carbs and he had tons of money, could have put in a richer power valve. TomO 09-20-2015 @ 4:40 PM reply profile send p.m. Senior Posts: 7271 Joined: Oct 2009 Did this just suddenly start or have you been living with it for 10,000 miles? Check your plugs for correct combustion. If they are the nice tan color, you need to look at the total rear end ratio and your driving habits. The total rear end ratio includes tire size. You can also look at front end alignment, brake drag, tire tread design and tire air pressure. IMHO 10mpg in the Bay area rush hour is normal for a flathead. Tom This message was edited by TomO on 9-20-15 @ 4:49 PM mrtexas 09-20-2015 @ 4:34 PM reply profile send p.m. Member Posts: 68 Joined: Dec 2011 Carb must be too rich. You need to use a probe in the exhaust to measure the actual CO or O2. There must be lots of partially burned fuel in the exhaust. The O2 sensor in modern cars is used by the ECU to maintain the optimum air/fluel ratio. In your case it would tell you which jet was correct for your car. I would guess that even easier would be to reduce the size of the main jet until loss of performance and signs of too lean of a mixture. What would you say to that Ken Ct? This message was edited by mrtexas on 9-20-15 @ 4:39 PM agriffey 09-20-2015 @ 10:29 AM reply profile send p.m. Member Posts: 28 Joined: Sep 2015 I am getting around 10 MPG, or less. if I drive 65 I get about the same mileage as when I drive 40. The main jets are no. 51. I am at 12 feet above sea level (San Francisco East Bay). It has the stock oil bath air cleaner, utility body level with top of cab but narrow like the pickup bed was, it will run fine without evidence of choking at high RPM's right up to 70MPH and over (around 3.5:1 rear end).. When I stop for a few minutes there is never evidence of the carb leaking into the intake. It starts the first turn and runs smooth with no smoke whether it sits a couple of minutes or an hour or overnight. I usually drive around 50 to 55 on the freeways. Oh, and I have been a full-time mechanic 60 years. I started working on only Fords in 1950 until I got a job working on all makes in '55. Thanks for the replies guys.

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