i will admit that im not the smartest when it comes to engines but i am pretty sure that when a fireball shoots out of the carburetor that is a bad sign. I thought it was cool for a second but then relized what could happen. Well my mom is going to make me sell it and i love working on it and im trying hard to get it ready for some insane 4-wheelin so i would appreciate any advice or help. This is what happened. i bought the truck a few months ago and we new it had a carb problem but ran good enough. ever since then it has gone down hill. i was hoping not to mess with the engine but i have had to. We rebuilt the carb 2 months ago, new plugs, new wires, new cap and rotor, new fuel pump, new ignition module, new voltage regulator and a new coil, and last week a new starter. Since i only paid $700 for the car and about $600 for everything so far including paint and a front driveshaft im not to worried. We can get it to run every now and then but when it comes time to get it inspected something bad happens everytime. today it still has a rough start even after i shimed the starter but it started and drove great after we reved it a while. slowly it got better and didnt sound like it was going to die. Then later i started it and it turned over then turned off and agian and then again but this time it sounded like something either got sucked into or shot out of the carb and i heard a little pooff and then i see a giant fire ball surrounding the engine. Not good to me. i dont knonw if the carb all together is shot but i dont want to start it again without having the problem fixed. Hopefully i dont have to sell it and lose alot of money cause that would really suck right now. if anyone can help. i know i have posted alot of help but im a little new to the engine area and that has been the only problem with the truck. But thankyou to all those who have helped and i hope this wont be the last post due to me having to sell the 78 ford. Please help. thankyou.
joseph

 

All I can tell you to do is check your ignition timing, check your float in your carb and make sure its not stuck and double check your firing order. You might have a spark plug wire crossed. A temp fix to stop the fire could be done by advancing the ignition timing about 5-7 degrees as long as it doesn't ping on you. Check the above first. Could be an easy fix.

 

Simply being cold can make the engine cough back up through the carb. Making sure your choke is operating correctly or going to a manual choke will help this problem. There are other things that are originally installed in different combinations to help keep it from running bad when it is cold: heat riser valves in the exhaust pipe, heat stoves around the manifold going up to the air cleaner, and heat passages in the intake manifold which can clog. Backfiring when cold is not good, but shouldn't cause a problem if you have the original enclosed air cleaner installed with an air filter. Also, does it run ok when warm, with no hesitation? If there is a hesitation when warm, your accelerator pump could be faulty, not squirting enough fuel when the gas pedal is tapped.

 

I had this same thing happening, and kept messing around with the carb adjustments, timing, ignition, everything else.. I ended up adjusting the carb WAY rich in order to compensate. Eventually the thing died, and I found out that blown exhaust valve guides were causing it all along. Take off your heads and have them inspected at a machine shop.... neglected exhaust leaks will eventually add up to this kind of symptom.

Note: Leaving the air cleaner on while tweaking the carb is a good way to avoid the fireball thing... it retards the flames for some reason. I noticed that whenever I tried to start it without the air cleaner on, I got a HUGE fireball out the carb. Good luck

Greg
67 F100 CCS 390 cruise-o

 

Joseph, Please check the vacuum advance on the distributor. I had a bad one on a rebuilt engine with a rebuilt distributor. The diaphram on the advance unit had a leak in it and caused a tremendous backfire through the carb. If you by chance have a holley carb on the truck and it has experienced a backfire through the carb, it has probably blown the power valve as well which creates a whole new set of problems. If you dont have a holley on it, just check the vacuum advance and ignore my ramblings. Mike
1977 F-100
300 I-6 / C-4 (soon to be AOD)
Offy intake w/Edelbrock 500CFM
Hooker Ceramic coated headers w/duals
MSD6
Whiter whites/Brighter brights

 

Joseph! Listen to your Mom. She is very wise and gives good advice. Save your money, get an education, invest in the stock market not old trucks. When your older and as wise as your Mom, you can buy a truck that runs from one of us!
William in Atlanta