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Posted By Discussion Topic: Gas hog -- page: 1 2     agriffey 09-19-2015 @ 11:17 PM reply profile send p.m. Member Posts: 28 Joined: Sep 2015 My '51 F1 V8 is using way too much gas. I have gone through the carb 4 times, replaced the vacuum advance module and set the timing at 2 Degrees BTC at a slow idle, At higher speed the vacuum advance pulls it up to 17 degrees, just as the service manual says the maximum advance should be. Is that really enough advance? The thing runs real nice and pulls well even with the higher speed rear end that I got from a '72 F100. It has about 10,000 miles since the engine was rebuilt. It was bored .040" over. I drive from 60 to 200 miles a day more than five days a week. ken ct. 09-19-2015 @ 11:50 PM reply profile send p.m. Senior Posts: 1513 Joined: Jan 2010 After 4 of your rebuilds maybe you making the same mistake over and over again.Depends what is contained in the kits your using.Rubber tipped needle and seat , rubber accelerator pump , wrong # power valve. Send it over and if I cant fix your problem all you will owe me is for the USA kit I use and return shipping. If fixed you can send me the rest of the normal charge. ken ct. 1-203-260-5945. I assume this is a 7RT or an 8RT. Send with any attached fittings and or brackets with it. trifordv8 09-20-2015 @ 5:41 AM reply profile send p.m. Member Posts: 3 Joined: Feb 2015 What size main jets are in the carb 40cpe 09-20-2015 @ 6:11 AM reply profile send p.m. Member Posts: 477 Joined: Jan 2010 "Way too much gas". How much is that? What are your expectations? How fast are you driving? The weight and aerodynamics of a truck work against fuel mileage. 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. 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 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 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. 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. 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

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