So, I’m new to the site, I have a 94 f150 4x4 5.0 m50dr2 trans. The efi has been deleted and I have a crate Motor 1989 5.0 flat tappet engine. It has a edlebrock 1403 with performer intake and msd ignition. Everything else in the truck is new. I was shocked to find that I’m getting just over 200km per tank (70) litre or for you yanks, 19 gal. Basically 7mpg. And that’s light footed city and highway driving. Any thoughts and suggestions would be greatly appreciated. Thanks, Steve.

 

tire size, gearing, and which cam came in motor, what do the plugs look like.

 

it’s all stock. 31” tires and whatever cam came stock with a 89 5.0 flat tappet still, 7mpg wtf!!

 

Single tank or dual?
What do the plugs look like?
Does the oil smell of gas?
Did you do the carb conversion or was it a PO?

 

plugs are a nice burnt toast to grey. So normal, dual tank but I only use the front. And the previous owner chopped all the efi harness and that motor started getting rod knock so I dropped a new one in. As much as I despise what he did with the efi, I can’t help but love the concept and simplicity of a good old carb. That’s why I put the money into it. Oil smells nothing of gas

 

Then I suspect half of each tank of gas is simply being dumped on the ground out the filler neck of the unused tank.

 

no, I installed a new tank that fits an 80 f150. Sending unit and inline pump. The rear tank has no plumbing connected.

 

Well then I guess that means you need to do some carb tuning.

 

So what kind of carb? Bet it's a 650 or bigger & if mechanical secondaries, then Bob's your uncle. (i.e., there's your 7mpg)

 

A 302 should be able to get 15 to 19 mpg with an overdrive trans and respectable final drive ratio. It doesn't matter if it has a carb or EFI.

The most accurate way to tune a carb is to install a wideband O2 in the exhaust. Just be sure there are no leaks or else it will be off. Target just a hair lean like 14.9-15.0 AFR for the best mileage when cruising.

 

Without knowing anything else about the truck, my fist thought is carb as well.

Other than driving habits, or something mechanically wrong. Check the carb and stay out of the secondaries. I believe It’s mechanical secondaries on that, go easy on the foot. you’ll have to see how far you can depress the gas pedal before you start opening them, they are larger jetting and bore as well than on the primaries. As soon a you get into them your fuel mileage will really go down. It’s not a particularly big carb, but 500 4 barrel, might not be the best for what your looking for.

Make sure your choke isnt sticking partway closed or something too.


Thats my 2c.

 

The 289 in my Bronco and the Jeep 304 came from the factory with Motorcraft 2100 1.08 venturi carbs. From what I see that is a 287 cfm carb. As said maybe you are way overcarb’d and dumping way too much gas into the engine.

 

according to the math involved when determining carb size per cube, it came out to 447cfm or something. My 1403 is a 500 which is the smallest 4 bbl I could find. It does have mech secondaries but I try too keep it under 3000rpm. I had a 1806 with vacuum secondaries and it’s a 650cfm and it had about the same economy as the 500. Like I said, everything is brand new. I do have a pressure regulator installed that I assume was pre set at the factory but I’m not sure.

 

Did you do any initial carb tuning? Where is your ignition timing set? Timing can have a large impact on mpg. Start with 10 degrees at idle and see where the rest is through rpm range without vacuum advance. Ad make sure the vacuum advance is hooked up that will kill mileage if it's not working.

With that said,

Any of the edelbrock carbs made in the last 15 years are questionable at best. Their quality has suffered immensely in the quest to churn out volume. If you want to keep it I highly recommend getting one of the complete calibration kits. I believe 1486 is the part number you will need. Also get a set of pipe cleaners and make sure that all the passages are clear and no chrome plating is flaking off of the inside of the fuel bowl.

Personal experience with these carbs has been hit and miss. Had some work ok and some that wouldn't run without a complete rejetting and adjustment right out of the box. Had one straight from the box that the float would not move because of the flaking chrome plating had it stuck.

They set them up from the factory on the mildly rich side to prevent people that dont know what they are doing from melting a piston.
They also need the float set about 3/16 of an inch lower than the spec book says I've come to notice. I dont know it it's the float design or material, but the same carb tuned and run on the track with 93 non-ethenol would show bowl overflow when filled with 87 with 10 percent ethanol. I'm thinking the density of the alcohol causes the float to ride lower in the bowl and allow the level to get too high and spill into the venturi well. I do my best to avoid them anymore. I, on my personal carbed projects wont run anything other than a quadrajet. Most of my friends run the holley street or truck avenger carbs with decent results.

What intake manifold are you running?

 

I’m running the edlebrock performer rpm manifold. My timing is set at 14 deg and my vac advance works. It’s all brand new.