backfire

jerry of whidbey

jerry of whidbey

Senior Member
Ok gentleman here is the problem. Almost the same as JD1931 went through.My engine is stock 31. I have changed every thing distributor,coil, plugs, points, retimed all one at a time.
I go about 5 miles the truck loses power and starts to back fire. Ican feather it home. If I let it set and cool off I can start it right back up and drive away for another couple miles and it starts all over
 
Try loosening the gas cap sometimes they don't vent. I just had one doing the same thing the spark was getting weak from a modern style distributor plate causing it.
 
Check the copper strap that runs on the outside of the flat spring on the points (it is kind of U shaped). I had this same problem, the strap is too long on some points and will touch the case of the dist. causing all kinds of problems. My '29 Tudor had this problem when I purchased it, took me many hours to find, as soon as it got warm the missing and back fireing would start, let it get cool and everything was fine. All that was needed was to put a little bend in the strap with a needle nose and the problem was solved.
 
Try blowing from the carb to the tank with compressed air. You may have a blockage in the line that won't come out with just fuel pressure as little as that is. Make sure you remove the cap before blowing it out.
 
blew the lines from carb back to the tank new condenser blocked vacume off at engine. took carb apart every thing clean. when it goes into the back fire mode amp gauge does not go to discharge side
 
Check and then recheck your valve clearances. Five miles is plenty of time for heat to do its thang and permit an intake valve(s) that is/are set too tight to sit up off its seat and cause symptoms that you describe.
 
As someone suggested, change your condensor before pulling other things to pieces; sounds like classic stuffed condensor.
 
Is it coughing, like out of the carb or backfiring, like out of the kzhaust???? or is sorta' missing erratically???? Bill W. (Check dist cap in the dark for arcing to plug connector straps.)
 
Well the number one rule in my books when an A (or T) is backfiring is that there is a vacuum leak at the carb or intake gaskets.

Another problem area is the pigtail wire under the distributor plate.

If the wire is frayed it can intermittently touch the distrib body and ground out.
As the vehicles dies/stops pulling, the ground releases and the vehicle pulls forward again and the wire again touches.
...As the engine warms up, any slight greasy film turns to liquid and if there is a slight greasy sheen inside the distrib body (as there was in mine), the grease turns to liquid and is then able to pass the current of things like frayed wires to the ground of the distrib body.
Having said that, The resulting jerky thrust of the confused engine doesn't necessarily cause a backfire but rather just a rapid on/off 'lurching' movement.



...I would tend to believe your problem may be in the carb/intake and delivery of air/fuel.

Again, as the engine warms the intake manifold warms and expands at a slower rate than the quick to rise engine.
If an intake/carb gasket were on it's last legs this is the exact time that it would become noticeable -shortly after engine start- in that the engine is hot and has fully expanded and the intake/carb is still rather cool.

At that time the greater thermal expansion of the block may be just enough to cause the smallest of crease or tear/imperfection in the gasket (or machined surface) to allow air to be sucked in thus throwing your carbs precisely metered air/fuel ratio out the door.

jmho, I would suspect the intake and or carb gaskets or possible loose/cracked manifold or bolts..


moe
 
It sounds to me like enough clues have been given that some possibilities can be eliminated:

1. If pulling on the choke makes no difference, then the problem is not fuel supply or vacuum leak related.

2. If the ammeter doesn't peg on discharge during the backfire episodes, then the problem is not electrical shorting in the primary ignition system.

To my mind, that leaves shorting in the secondary igntion circuitry, which wouldn't peg the ammeter, or intermittent "opens" in either the primary or secondary ignition circuitry. Try another condensor and coil.

Steve
 
When did this problem start ? Did it just start all of a sudden on its own or after you did something ? From what you describe it sure sounds like a classic fuel vent/delivery or condenser issue. But, I guess you checked all that.
 
I too would suggest a different condenser. Even if you put in a new one, it might have been flawed. It's a cheap thing to try before you get into more complicated solutions. Occam's Razor, y'know.
 
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