Hey guys I have a 1984 f-150 302 with an Edelbrock 600cfm carb manifold back exhaust ARP head studs and head gaskets done 1500 miles ago or so. My problem is anytime I try and get to about 3500 or 4000 rpms it will fall on its face and then backfires out of the exhaust and carburetor, the truck ran perfectly fine last night and months prior. Would really appreciate some opinions on what it could be.🙏🏻

 

I don't know but I wouldn't keep recreating that scenario if you like your exhaust.

 

If it were mine the first thing I would do after checking for a vacuum leak is take another ignition control box and try it. You don't need to even mount it just plug it in and lay it on the backside of the fender liner and take a test drive. After that I would look for a fuel starvation issue.

 

If none of that gets you anywhere and the mood gets grim I would take the valve covers off and look for a rocker arm that doesn't seem to be participating like the others or a stuck valve. Check crankcase oil level as well.

 

Bad coil, bad wires. Ignition breaking up? If it otherwise idles fine I’d look at the ignition first.

 

Sounds like a lean condition to me. Up at that RPM the carb/fuel supply is not keeping up for what ever reason. Intake and Exhaust backfiring is symptomatic of lean fuel air mix.
I would start with the fuel filter/s, Fuel pump flow, and fuel feed. Then look at the carb. I highly doubt this is an ignition issue. I would check the fuel system first. Then move on to the ignition system.

 

As 82_F100_300Six stated, it may be your ignition. I had a truck with the same symptoms and it was the Ignition module. Start fine and ran well at low speed but upon acceleration up to highway speed, pow pow! But, these things keep you guessing.

 

Don't over look plugs even if they look good.
I had 1 truck I drove about 100 miles just fine. Shut down for 8 hours or so and on the drive back home it started missing & back firing out the exh. any time I hit a hill.
Changed plugs and all was good.


Also had a car that I only ran to get on/off trailer or to move around. Started 1 day to move and it back fired out the exh. at anything above idle. Traced it to bad plugs and they looked brand new.
Dave ----

 

I don't understand spark plugs. I have an old stihl 026 that quit running. I put a new pulse hose and carb kit in it. So it would crank up and run like gangbusters for a few minutes then quit and let you pull your arm off trying to restart. It was really frustrating. Out of desperation I put a new spark plug in it and it was cured.
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Use timing light and Tune it right 🤦*♂️