I have access to everything I need to convert my TBI over to a Carter 2 barrel setup, which came off a '71 Satellite. I don't mind the "mechanical-ness" of carburetors, I see it as less potential electrical problems (everyone's favorites). I think I'm squeaking out around 14-15 mpg from my TBI now, just wondering if the carb would get any more out of it. It seems like the TBI runs pretty rich, and there's no way (that I know of) to change that. It'll never be a Prius, but if I could get another 2-3 mpg out of it, that'd be nice.

 

Its all about the tune. Understand the carburetor and test it until you find the setting that works best.

 

What mileage was on the engine it came from? Carburetors do wear and with that wear comes decreased mileage and an inability to properly control the mixture. It is hard to judge what will happen without knowing what shape the carb is in.

I assume you realize that you will also have to replace the entire engine control system. This will also effect your mileage and again without knowing what engine control system you are going to use it is impossible to predict an outcome.

If you are looking for mileage and are going to go to this much trouble to switch to a carburetor. Why would you not choose a 4 barrel?

 

The carb is new. My dad was having trouble getting his 318 to run right so he got a new carb for it, but it didn't help any. He ended up swapping in a pretty hot 383 and a 727 trans, so now he has the complete 318 just sitting around. So the reason for the 2 barrel is because it's free lol. Before I did anything extreme like that, because I realize it's alot more than just swapping the manifolds and carb/TB, I may check timing, I've seen people have gone with as much as 12* with good results. Also, I wonder if the throttle position sensor can be turned forward enough to help with the richness issue.

 

have you checked the codes to see if there are any to indicate why it is running rich or done any diagnostics?

 

Yes, no codes, lights, anything like that. I've heard time and time again that the factory setup tends to run a little on the rich side though. In fact, the truck runs great, I'm just trying to make sure there's nothing I've overlooked in my quest to get halfway decent mileage. I think 14-15 is pretty good for what it is, but if there's a way to squeak out a couple more mpg, and doesn't cost more than the benefit, I'm all for it.

 

Just because somebody runs '12 degrees' of whatever does not mean YOU will run fine on that. Your situation as far as combustion quality can be totally different than the other person's mill.

What is the engine doing, and when in the rpm range does this or that happen? Have you gone through any diagnosing procedures for it to fix what is wrong? Reading the plugs is not very helpful anymore since oxygenated fuel does not leave residue as much if at all anymore. However you can see if the electrodes are rounded from heat, replace them!

Things to consider for mileage:
Tire design
Intake system
Exhaust system
Gear ratio
Aerodynamics
Vehicle weight (You don't use your vehicle as a storage unit correct)
Alignment
Wheel bearing condition
Engine oil condition
Engine oil quality
Transmission fluid quality
Transmission fluid condition
Drivetrain condition (do you grease your u-joints periodically, change trans filter etc)
etc
etc
etc

Thesel and more equate to reducing friction and improve fuel mileage if serviced properly!

Does the carburetor you are wanting to use have exchangable boosters?

 

Think about it like this, as your rpms go up, your throttle moves forward allowing more air to flow through the induction into the cylinder, In oder for you to feed the engine at higher rpms you need more atomized fuel so no IMO.

There is a programmed setting in the computer for fuel pressure and the factory jet size, I doubt can be changed (although I am not a efi guru). The issue with TBI is there is still deterioration of atomization quality as our atomized fuel travels to the combustion chamber, Carbs have the same issue. If both of these units are optimized though, the issue will be reduced. This greatly effects mileage depending on severity of fuel dropping out and puddling. Many other factors play into this situation though as well.

 

89ram150; Have you looked at the injector spray patterns? One of the advantages of TBI over other injection systems is the fact that the home mechanic can see the patterns and spot injector/fuel system problems.

 

No sir, recently, I have not. I've taken the whole throttle body off in the past and cleaned carbon out of vacuum passages, cleaned the throats, etc, but have not done anything to the injectors themselves. Can they be soaked in a bowl of carb cleaner or with pressurized air, etc?