Poor mpg

Wumbo · Jan 19, 2020

Rusty Nail said:
before / after , what difference does it make anyways!??

serious though.
If your ignition REALLY IS set at 10° before top dead center , that's your problem.

Reset timing to 10° AFTER top dead center, take two aspirin and call me in the morning..

Don't bother posting without a pix.

Hope this helps!

Les Maples · Jan 19, 2020

I'm hooking the timing light up here in a few and reset timing and see what that does.

Frankenchevy · Jan 19, 2020

Les Maples said:
I'm hooking the timing light up here in a few and reset timing and see what that does.

It’s definitely btdc. The flame front takes a certain amount of time to travel and you want it to explode at optimal cylinder pressure shortly after tdc. The faster your engine is spinning, the longer this can take, hence why advance will send it out to greater than 30btdc

if you aren’t pinging at wot with 8 degrees base, you’re in the neighborhood. Just make sure you’re checking it with vac advance disconnected. Then rev it out to ~3k and check to see that your mech advance is working. You can then reconnect your vac advance to full manifold vacuum and watch that it advances your timing at idle.

Les Maples · Jan 19, 2020

Ok 10 after tdc starts easier for sure. I will see in the am when I go to work. Thanks for the help. I'll update you tomorrow

Frankenchevy · Jan 19, 2020

Check for vacuum leaks. Could be tiny splits in any of the black hoses or caps under the hood. If your dizzy vac advance is starved for vacuum, it will affect cruise performance significantly. If it’s not vac advancing, it’s igniting too late. By then the piston is already too far down and you’re wasting gas. It’s like trying to push a kid on a swing but she’s just about traveled beyond your reach. You might barely connect at the end, but it was a wasted motion.

SirRobyn0 · Jan 19, 2020

For your reference I have an 84 C20 350 700R4 I get 12 on my drive to and from work which starts out as county roads and ends in city traffic. On the highway I get a pretty consistent 16. 5 is terrible. BTW ignition timing should be BEFORE top dead center not after, 10 BTDC would be a little high for some 350's. I would be looking at the carb. The only time I have ever run into such a severe mileage loss that didn't have an obvious cause someone had put HUGE jets in the carb. Oddly enough that rig ran good and didn't foul plugs. Another thing might be if the timing chain is full of slop, or somehow running off a tooth, but you'd have a pretty severe power loss to go with that.

80BrownK10 · Jan 20, 2020

Les Maples said:
Hello, I just got this about 3 months ago and put a 350 in has a 700R4 with 3.08 gears. It was a total mess and now it's a daily driver. Love this truck.

Something bid bad wrong!! You sure you don't have a fuel leak? Are you timed right, carb adjusted, tuned up, brake not on, engine has any compression left?

I have a 350/350/205 k10 with 3.08 gears and I get about 10 mpg. I can get close to 12 if I want and drive slow. I get 8mpg pulling a 5-10,000 pound trailer. Oh and I am running on 33's.

Rusty Nail · Jan 20, 2020

BID BAD!

AZ-520 · Jan 20, 2020

What's the general health of the engine, compression, timing chain slop etc. I like to run AFR gauges on carbs jet them just right. Sounds like you are getting there. Keep eliminating possibilities.

80BrownK10 · Jan 20, 2020

Rusty Nail said:
BID BAD!

Haha. I don't know what my phone did there. But I think I was trying to say "something is bad wrong". Or "something bad is wrong"?

Dang autocorrect and put what it thinks you wanted to say.

Lefthand6 · Jan 20, 2020

I recently put a new carburetor on my c10 with a 350. One side of the carb was all the way lean (with screw ceased). The other side was all the way rich to make up for the lean side. The choke linkage was also broken. I was getting maybe 3 mpg. Now I am getting closer to 10 mpg. This is also moving my timing back from 16° tdc to 8° tdc.

ali_c20 · Jan 20, 2020

My mpg also sucks but that's directly connected with the behavior of my right foot....

Colin · Jan 20, 2020

My '78 K10 (350/TH350) runs about 8 mpg, which is pretty normal for these 4x4s, I would say.

Raybo135 · Jan 20, 2020

As I have always said about driving these trucks, "It is not miles per gallon that you should be worried about, it is SMILES per gallon. I was getting about 6.85 until my friend notice I had a short in my EFI and was firing the EFI all the time. The Electric Fuel sump was constantly clicking on and off. I am getting much better now. I have gone about 40 miles on the last fill-up and it hasn't moved off the Full mark. Fingers crossed! ! !

tubehead · Jan 20, 2020

350HO 700r4 9 inch ford

You must be registered for see images attach

diff 3.5 gears.Rebuilt quadrajet getting 16.8mpg driving like a granny around town.6mpg driven hard.

Poor mpg

Wumbo

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Les Maples

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Frankenchevy

Proverbs 16:18

Les Maples

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Frankenchevy

Proverbs 16:18

SirRobyn0

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80BrownK10

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Rusty Nail

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AZ-520

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80BrownK10

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Lefthand6

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ali_c20

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tubehead

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