Hello all, new guy with questions

[spartman]

Howdy all, I have been lurking here for a bit and I guess I have some questions for you guys.

What I have is a 1980 1/2 ton 4x4 Custom Deluxe pickup.  It has a GM Goodwrench 350 that has about 20,000 miles on it, it has an Edelbrock intake, stock manifolds,dual 2.5 inch exhaust and I put a new accell dizzy in the motor when I got the motor.

It also has a turbo 350C transmission with the lockup connected to a flip switch.

The axle tag decodes as RAM which says it should be a 2.79? gear IIRC.


Okay now to the questions, I am currently only getting a best of 10mpg in it no matter what I do with it.
I have tried a couple of different Q-jets, also have tried various rods and jets inside, no change.
Also I have put a 2 Bbl Autolite carb on it no improvement in mileage even when I accidentally ran it to lean with 49 jets in it, it now has 52's that it likes.

Also the tranny is a 2wd version cause it was eating my 4x4 trannys up for whatever reason, and I needed the truck for work so I just converted it over to 2wd for now.

This truck also has just enough power to get out of its own way but thats about it.

Would putting a tbi intake and setup from a 88 1/2 ton improve the mileage or is 10 gonna be the best I get no matter what?

Sorry bout the long post, just want to make sure I give you all the details I can.

Thanks guys.

[Prong]

Is it a fulltime 4x4? Because if you're running that thing without lockout hubs and the transfer case isn't converted to part time, you're using a lot of energy needlessly. Coverting to part-time would net you at least 2-3 mpg most likely.

[spartman]

It was a part time NP205 transfer case.

the hubs were unlocked.

Now the truck only has a 2 wd setup.  The front end is just along for the ride now.

[choptop]

You are still pushing alot of weight around up front, but 10 mpg is a little excessive. My bigblock does better than that, and my 86 with the 305 gets 18, but that is with a 700r4.  My question is, are you running the stock size tires on it or larger, if larger, how much? With 2:79 gears, if you are running a larger tire, then that is where your gas mileage, and power is going. If you are still stock, I would venture to say you are having a ignition problem, either timing or low ignition voltage. May even be spark plug gap. If the distributor doesn't have the right advance, then that could also be an issue. There are some awesome guys on this site, someone will get you on the right path. As for the fuel injection, it will help, but with the carb and ignition setup right, fuel mileage won't necassarily be better with fuel injection. I have a 51 Chevy pickup with a 235 six cylinder that gets 20mpg with a carb, so I don't think you'll see enough difference to justify the cost.

[Blazin]

My 84 K10 was the best truck I have ever had for mileage.
 Just for reference. When I got it it had a pretty stout 283 in it. With an SM456, 2:73 gears. & 31x10.5s it got 18 / 19 MPG. When the 283 blew up I dropped an 86 305 in it. The mileage went up to around 21 / 22 MPG.
 My Blazer with 350, TH 350, 3:08 gears and 35x12.5s get around 14 MPG.

[Lt.Del]

Make sure your timing is correct.  If you have wheels that are larger than stock, as mentioned, your rear ratio is converted to an extremely high gear w/ the 2.79.   I have a 3:08 and want to  convert to a lower gear like 3:73 or so. The reason is, I do little highway driving, therefore, need more gear for city driving so I won't have to give it so much gas to get 'er going.

[dumbucket1]

I dont see how you guys are getting that kind of mileage, i cant get more than 9 or 10 mpg out of any of my trucks and I drive them very easy.

[autorepr]

Maybe stating the obvious but,,,, No fuel leaks?  I put an engine in a guys truck that had been sitting for a couple years and he went nuts on me cuz his fuel mileage was low. I told him the tank was leaking and he refused to accept that. He didn't have the money for a tank, then when the fuel pump went out we had to drop the tank. I put a pump, sending unit and a tank in it. Bingo 18 mpg!!!!!!!!!!!!!!!!!!!

[Blazin]

My 79 K30 dump 350, SM456, 205, & 4;10s gets 13 to 14 MPG. My New truck 86 K30 dump 454, SM456, 205, 4:56s gets about 8 to 10 if I drive it nicely.

[spartman]

I have the stock 235/75/15 tires on the truck.

I had thought about a fuel leak but couldn't seem to find one, I do have dual tanks on this truck and if it were a leak its not in the tanks.

I get the same mileage on either tank.

I know if I had a leak on the suction side of the fuel pump the truck would run rough and of course be sucking air.

I have replaced the fuel line from the pump to the carb and no changes in mileage there.

How would one go about seeing if the dizzy were set up wrong?

I have set the static timing to 8 degrees like the tag says and no change, I have also tried to advance it to 10 degrees and absolutly no change.



As far as the fuel injection stuff is concerned I have everything but the efi dizzy already from another project so the cost of it would be minimal.

Thanks for your help so far guys.

[autorepr]

You could actually be pumping a small amount of fuel from one tank to another through the return part of the switching valve. When it's running some fuel is pumped back to the tank mostly at idle. The switching valve has two valves in it, the one for suction to the pump and one that returns to the tank. The return could be leaking into the other tank and all you would see is increased fuel usage. You could bypass the switching valve completely and run off one tank and recheck it.

[spartman]

If it were leaking between tanks wouldn't the emptier tank start showing fuel on the gauge?

Mine doesnt.

[zieg85]

a 20,000 mile 350 should be fairly responsive.  You said it would barely get out of its own way, check the ignition.

[Bubba13]

You might check to make sure that your camshaft if correct for your aplication.

[spartman]

The camshaft is whatever GM puts into their 350 Goodwrench engines.

I suppose its possible that its the wrong one from the factory.