So I was driving to work today in the ol' 76 F-150 (300 6cyl, auto) and things were going fine. I was cruising 60 - 65 mph when all of a sudden the engine stumbled and lost power. It was still running but it would not rev up or gain any power. I began coasting over to the shoulder when it backfired really loud and shot flames out from under the hood. I got off as fast as I could but not before it popped and breathed fire again. I quickly shut down the engine. I waited a minute before opening the hood in case a little fire was brewing. I opened it and found no fire or evidence of anything burned. I closed the hood and started on my way. The engine started up normally and sounded fine. I got back on the highway and got up to about 50 mph when the engine stumbled again and lost power. I quickly shut the engine off and coasted onto the shoulder. I waited a minute and started the engine. Everything was fine so I continued on to work no higher than 40 mph and it was fine.

What happened? It has stumbled a little before but it has never shot flames from under the hood. Everything sounds fine but I'm a little leery or driving it on the highway. Any help figuring this out would be greatly appreciated...

 

If it goes back to "normal" I'm thinkin ignition. Do you have the Dura Spark ?

 

Test your ignition box at the parts store for free. If it is bad buy a Motorcraft unit and mount it 1/4" off the fender with spacers.

Check your fuel delivery also, I have had a fuel pump fail with very similar results.

 

Upom further inspection last night, I do have the Dura-Spark distributor. I checked the timing and it is right on the money. I took the back way home from work (under 50 mph) and it ran fine. Cap and rotor are in good shape, as are the plugs and wires. The problem seems to be more of a carburetor problem. It almost seems to be loading up when it is cold. It was a bit cool out this morning so I let the truck warm up for about 10 minutes before I left. I got up to about 60 mph on the way to work and everything was normal. Is there anything I can do to the carb to make it run better when cold? It really stumbles bad if I don't let it warm up for 10 minutes or so. Thanks...

 

The choke may need adjustment to improve cold engine performance. Take the ignition module to a parts store for testing.

Your carb power valve may be blown due to the backfire.

 

Where is the power valve on the YFA 1 bbl?
I had mine a part lastnight to adjust the excellerator pump and the metering rod but I didnt see a power valve , well one that looks like a holley's power valve at least?
I think you may have a plugged up fuel filter, but I agree with everyone on the spark box diagnosis .
Get a manual and run a few tests , like a fuel pressure and a volume test ,( you can get a vacuum gauge with a fuel pressure gauge combined in one gauge).
At ide you should have 5.0 to 7.0 psi and 1 pint in 20 seconds (volume), from a healthy fuel pump .
Once the engine is running at idle pop the vacuum gauge on the ( manifold vacuum) and see what you are running 16-21 inches of HG is normal-depending on your elevation .
Post your results !

 

Thanks for the catch, I have to remember this is a six with that 1 barrel carb on it. Too many posts to check sometimes. That design is not subject to the same blowout problems that Holleys and some other Motorcraft carbs have. That metering rod setup kind of works like a power valve.

 

take the computer to the auto parts store and see if that is it... I will bet thats all it is... if it was your carb then you would prob. be geting not enough fuel, it sounds like your not geting any spark .... loading up on fuel and then it gets spark and ignites all of the fuel built up in the exhaust and intake and comes out your carb.... sounds like its just one or two cylenders that are not geting any spark.....

 

I am not knocking you Torque1st I just wasn't sure if (I) missed something on my YFA-it was the first yfa I have rebuilt
I think Racerdave is onto something , plugs, wires and rotor+cap might do the job-at least check them out !

 

wow thats a first... Tourque1st deserves some of the credit... thoes books I read really helped.... Thanks Tourque1st! For recomending I look into my local Library for information on Understadning and Troubleshooting Engines. I would recomend everyone do the same! It gives you a better understanding on what is goin on inside of that Block, and with all of thoes wires! Also : Replaceing Plugs, Wires, Cap and Rotor are a good start, but it is free to get your Ignition module checked out at a local parts store (call befor brining it in tho..). And if I were you I would adjust the choke on the carb, my 74, inline 6 does the same thing when cold... Have to let her run for a while and then stomp on the gas to get the idle down.... I dont mess with her tho... she will run forever.... (also has a bad leak in the carb to intake mount..) Screw holes are striped and havent messed with it much.. Still runs strong! Gotta love FORD

 

it isn't electric, or it wouldn't have anything to do with speed. I agree with th individuals who have assumed fuel delivery. I would replace the feul filter(s) in your truck and question the fuel pump if it keeps doing it.

Did you check the fuel pump yet?

 

I disagree.. and agree at the same time, what I dont understand is how would there be flames from under the hood if there is no fuel? I figured the only way that fuel can ignite under the hood is if there is fuel to ignite?if the intake valve is open when you get spark and it ignites in your intake and through your carb and out your air cleaner, and for the flames coming out of the exhaust, you must have extra fuel vapor in the exhaust (mixed with air) (so that would be a cylender that did not ignite properly, and the next time arround you get spark and bang, flames shoot out the intake when the valve is open and when the exhaust valves open some fire can still be in the cylender and ignite the fuel in the exhaust. I would replace the fuel filter, mark and take out the mixture screw and blow it out with some air (or make sure the passage way is clear) and make sure your fuel pump is operating normaly. I have had a similar problem with my inline 6, it would backfire when going up a long hill at arround 60 mph, OHH DUHH... I dont know why I didnt think of this befor, my problem was my points, I replaced the contacts and gaped them properly and never had the problem again....? That could be another thing u can check out if u have points...

 

Millertime, It can still be electric with a speed or load change due to how those systems can fail.

 

Just a thought- maybe the vacuum advance?

 

hmm.... if it were the advance.... you would have a problem with vacuum....I once stalled my truck on the freeway and I had to stop befor I could start it again because the advance was stuck? It never happend again, but I would do what people have said first and if thats not the problem then continue on looking and thinking of possibilitys.