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Old 09-27-2007, 08:35 AM
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Horrible gas milage in 81 C 10! Please help!!

I finally purchased the truck of my dreams but the gas milage is HORRIBLE! It is a 350 with a Holley 600, 9.5 to 1 compression I belive, a Comp Cams RV cam, and 3.08 gears. I was thinking the carb or timing needs to be adjusted? The truck is hard to start and I belive the distributor may not be very tight. The owner recently installed the motor and it only has around 100 miles on it and I'm still in the process of breaking it in. On my 80 mile trip home, I left with 3/4 of a tank and had to stop and fill it up. Could the gas gauge possibly be off? After I put $40 in the gas guage went a little over full. Any suggestions please HELP this is my daily driver.

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Old 09-27-2007, 08:46 AM
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First thing I would do is make sure the timing is correct. Check base timing, mechanical advance and vac timing. Make sure it is all correct. With a daily driver looking for fuel mileage you will need vac advance working correctly.
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Old 09-27-2007, 09:42 AM
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Be sure your carb is adjusted properly then check your timing and set it to specs. Another thing to consider also is the thermostat......what degree do you have? A 190-195 thermostat will give you better gas mileage than a cooler one will.
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Old 09-27-2007, 10:06 AM
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I will try to adjust the carb and timing, been looking online for instructions. I figured it would have to be either timing or the carb or both. I am open to any suggestions as how to adjust these items. I am looking at the Crane kit that has he adjustable canister and I'm thinking about installing different springs and playing with the timing that way. Thanks for the suggestions and the response.
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Old 09-27-2007, 10:47 AM
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Check that the choke isn't sticking
Shane
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Old 09-27-2007, 01:35 PM
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Adjust the valves to. This helped me with starting up my 4 cylinder.
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Old 09-27-2007, 02:36 PM
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Thanks for the info. I will check into adjusting the valves too for the starting issues. If the choke is sticking is it very noticable? This is my first carbed vehicle.
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Old 09-27-2007, 02:53 PM
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Quote:
Originally Posted by pete379
I will try to adjust the carb and timing, been looking online for instructions. I figured it would have to be either timing or the carb or both. I am open to any suggestions as how to adjust these items. I am looking at the Crane kit that has he adjustable canister and I'm thinking about installing different springs and playing with the timing that way. Thanks for the suggestions and the response.
Use the search function on this site for timing information for your 350....it has been discussed a lot here.
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Old 09-27-2007, 05:04 PM
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Do you have a number for the gas milage?This will help diagnose it more accurately.
Shane
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Old 09-27-2007, 05:39 PM
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If you drive conservatively, with a 350 4bbl, 3.08's and if you have a 700r4, maybe 12-15 MPG, if no overdrive, I would guess 12-13 mpg.
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Old 09-27-2007, 06:37 PM
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low milage.....

HI,check your air filter,pull it out and take a SHORT drive to check milage,if not better,,timing,Carb adjustment,take it to a shop with a distributer machine.
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Old 09-27-2007, 07:26 PM
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now my long 79 w/4-spd/3.08/454 will get 15 all day long on the hiway if I can keep my foot out of the secondaries.

if this is a short truck-----16 gal tank- I would be guessing 12 gallons to go 80 miles is coming to 6.6mpg, perfectly acceptable mileage if you are towing 8,000 pounds behind you.

long truck would come to 5.3mpg.

not really acceptable mileage on a daily driver.

I have had a few of these 73+ trucks and the fuel gage has been pretty accurate on all of them----to the extent that I can guess within 2 gallons what it will take to fill it up.

One was equipped with a 305/AT/3.08----21mpg on the hiway @ 60 (fed speed still 55)

Absolutely no reason to not get 14-15 hiway----10city with a 350

Bryan
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Old 09-27-2007, 08:11 PM
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I have a 73 blazer with a 350/ 4 speed and it had 3.08 gears and never got better than 12-14 MPG. It has some edelbrock RV cam and manifold, with a spreadbore holley on it..

I put 3.75's in it and it didn't make any real difference.

I set my gas sending unit up to show empty when there was still 5 gallons in the tank,(it has a 25 gallon tank), so the first 3/4 goes pretty fast.....so maybe you need to get an accurate fuel consumption number by running a tank of gas through it and measuring the gallons used at the pump /miles driven.


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Old 09-27-2007, 09:08 PM
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I would do the base line miles driven and how many gallons it used before I started too many tume up deals..Gotta know where we are at at this time..

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Old 09-28-2007, 07:58 AM
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Thanks for the replies. I not too sure of the actual numbers but it isn't great. I will replace the air filter as it looks fairly dirty. I figured it would get around 12-15 on he highway. but its way lower than that. I tried to check the timing but I dont have the timing tab? There is a 2 piece timing cover and maybe he fogot to install it? If so can I just buy one and install it?
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