I recently bought a 64 f100 with a 292 v8, bone stock. Drove 20 minutes home and it ran just fine.

I put patriot headers to flowmaster mufflers on it and now it backfires all the time and it will feel like it is running out of fuel when it has plenty.

Since I increased the airflow so much wouldn't it make sense that I need for fuel to match the adequate ratio? How would i adjust the carburetor to do that? or do I simply just have to re-jet it? I've turned a few idle screws in my day but I do not have much expierince with a carburetor other than my snowmobile.

Any ideas or advice would be very much appreciated, thanks,

 

Backfiring through exhaust or carb?

 

Sounds like from the carb.

 

If it coughs up through the carb, its outa time....ie timing chain likely slipped....if it's just backfiring or severely missing out the pipes, then ignition timing is off

 

Even though I drove it home 20 minutes and it ran just fine then next day ran it with headers and it started doing this? I feel like it would be hard to believe that it was just a coincidence that with headers the timing got off.

 

The headers would have nothing to do with causing the timing chain to slip (being stretched because of old age it could get excess slack causing it to jump a tooth on the timing gears placing the cam/crank timing out of phase) or the ignition system being out of phase. However, it might cause a lean out condition that would be a "stumble", that would require a carb adjustment (fuel mixture).

 

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The first easy thing to do is check ignition timing, and adjust if necessary. Set initial timing at 8-10 degrees.

If the carb is the original 2V, it doesnt need to be rejetted. There isnt much that can be done to it in the relm of tuning. The front of the accelerator pump rod should be in hole that is one down from top. The rear of the same rod should be in the inside hole. The two screws adjust idle mixture, and the one screw adjusts idle rpm.

If the backfire is actually through the carb, it could have blown a power valve. Sounds like the carb could use a kit and thorough cleaning. Kits include new PV and accelerator pumps. It would be a good idea to have someone else rebuild the carb.

There should be a filter between fuel pump and the carb. Change the filter and any synthetic fuel line between filter and carb. Clean out metal fuel line between filter and carb with brush and carb cleaner.

An engine with over 50 or 60K since last rebuild, needs a new timing chain and gears. Refer to shop manual.

 

I understand that this is all good things that I should do but the truck wasn't having any problems when it had the stock exhaust. The owner before me drove it plenty and never had it backfire. So all this started happening the second I put headers on the truck. I will definitely get working on all that other stuff. But more air means you need more fuel, correct? So i just wanted to know how to do that.
By the way I do not think it is the original carb, it has an autolite tag on the carb.
Thanks, Cole.

 

The original carb is an Autolite. Tag should start C4... The headers and mufflers dont mean necessarily more air, but less exhaust pressure. Air intake is limited by the carb, restrictions in intake and head intake runners, the small 1.64 in. intake valves, cam, etc. I understand the coincidence with running badly and addition of new exhaust being perplexing. Perhaps the change in dynamic has caused worn exhaust valves/seats to come to the forefront. Dont know, but all the other things need to be addressed anyway. So I would do them and if no change start thinking heads.

 

Let me try another direction. Say you want to increase the intake flow of air and fuel. There isnt anything to be done with the current carb which should be a 1.02 venturi, rated at a maximum of 247 cfm, except to make sure it is working properly. A different 2100 could be used, like a 1.08 venturi originally for a 302, rated at about 287 max. But this may not cure the present problem. Please dont take this as a recommendation to go out and get a new carb.

Still more flow can be provided with a 4V intake and carb, and better flowing heads. The better heads will have larger intake valves than the 64, but the same size exhaust valves. They also will have smaller combustion chambers for higher CR.

The primary limiter to flow is on the intake side.

A compression check on the cylinders should yield useful information.

One more thought, check condition of plug wires and possibility of crossfire. Is there one or more wires that has been burnt by the headers?

 

The only thing i would think differently on is with the timing chain statement that at 50-60k miles they should be replaced.......if it were a belt i would agree 100%, but chains typically last for 100k + miles (though it would not be a unique thing to have one stretch a little and jump a tooth requiring a new timing chain)

 

I do think it is a tuning issue, either timing and/or fuel. Adjusting idle screws will not accomplish what you need. You need to change jets, if that's possible with an Autolite. I don't know much more than what they look like from the outside.

But don't rule out coincidental issues. It's not uncommon for one change to be made and almost immediately another problem arises that is unrelated, particularly on old trucks.

 

Yes I was thinking stretching too, leading to retarded cam timing. On changing the jets, that will potentially richen the A/F mixture, but it isnt known yet if that is something that needs to be done. It is not recommended to go up or down more than 2 jet sizes from the starting point on 2100s. So beginning with a 46 jet in the 1.02, a person could go up to 48, maybe push it to 49, but IF NEEDED. If someone has already gone to a larger jet and a 48 is found installed, that doesnt mean they can be raised to 50's. Add another to do to the list, check spark plug color.

Lot of if's, and's and but's.

 

Was this ever resolved? I was leaning towards crossed plug wires.