I have a 77 f150 with a 351m. Just swapped the intake and carb to the 4 barrel. Now wants its warm is looses power, sputters, and if I floor it it backfires out the carb. I've replaced the coil, put hotter plugs in, I know I have good fuil flow, brand new air filter. I'm letting it warm up before I drive it and I can only go about 5 to 10 miles before it decides to run like crap. I was thinking it might be a cracked distributor but I'm not sure. Any help is apriciated.

I would check for vacuum leaks and make sure your choke is functioning properly. When you swapped the intake, did you remove the distributor? if so, double-check your timing.

Done, done, and done.

Was the carb a new or used unit?

Have you checked the cap for cracks and rotor condition?

Carb gasket good?

Carb is new, gasket is good. I'm on the side of the highway now replacing my dizzy cap to see if that does anything.

Cap did nothing except make it backfire out the exhaust.

You didn't get any plug wires mixed up?

First thought was vacuum...next thought is if it's sputtering and backfires when you floor it...to much fuel. Float level set too high???

I read something about a ford motor have a different fireing order from the rest. Gonna check that again. After last night smelling the exhaust I think it might be sucking more fuel than it needs. So I wonder if something in the carb is stuck full open. If the wires don't fix it that's what I'm gonna check next.

I would check for a bad coil. It may be breaking down once the engine heats up.
Does it start and act fine after it cools back down?

yea, once it cools down. But it's a new coil. That was the first thing I thought it was.

Just checked to see if the dizzy was 180 out. That's good. The firing order is right, the coil is new, high output, carb is new, but sat in a shed in its original packaging for about a year. I'm thinking the float is stuck and it's squirting too much fuel into the motor, it smells really rich at all times.

I also checked to see if it was trying to drink coolant or oil. It's not, all my vacuums are correct, I used starter spray to see if one of my gaskets are leaking, that's good too.

I'm thinking if the carb doesn't fix the issue next would be something deeper in the dizzy, I'll replace that with an HEI considering I want to do that anyway. And if that's doesn't fix it the only thing I can think of would be my timing belt tensioner is loose and my chain jumped a tooth on the cam.

Let me know if you guys have any other ideas.
And thanks for all the help! I really appreciate it.

Do you still have the old coil around?
New isnt always "new"
Just for a test, to keep you from chasing ghosts, might be worth a try to change it

What's the specs on that carb?

Edelbrock 600.

Hmmm, should be just fine for that engine then...

I think I found the smoking gun. The pos wire bolting to the coil was sparking between the end of the wire protruding from the connector to the post the the coil. As if the connector wasn't making a good enough connection on the wire. I'm gonna hook it right up to the battery to see if I can the girl home to fix her properly.

Let us know how you make out.

I had a brand new Edelbrock that one of the floats were bad. From what I found out, common problem with the floats.

Check and see if the choke flap is returning once she's warmed up