Backfire

[tbirdtbird]

Are you using crapahol or pure gasoline?

[fashion frank]

Originally Posted by fashion frank

I am having the same problem but my 31 just died after the backfire.
Here's what happned .
I just bought the car ,it is ( or was) turn key ready.
Brought it back from PA, drove it around the hood twice with no problems.
I know how to drive a standard but got my model a start up and shifting education from youtube .

Now the last time I took it out again, very close to home just to get the oil hot enough to dump, I noticed it was almost stalling every time I came to a stop .
So I pulled off the main drag , adjusted the choke /carb jetting knob a bit to try to get it to run leaner or as I hoped to stop it from hesitating at a stop.

Well that was a mistake because I then pulled back out onto the main drag and went about ten feet ,it backfired ,drove " rough" for about another ten feet and then died.
I managed to pull into a side street and had to have it towed the two blocks from my house.
Before I had it towed ,I tried to restart it , it would just crank ,but not turn over and there seems to be a smell of gas so I checked and there was in fact a good amount of excess gas , I assumed that I flooded it ,so I waited a while tried it again and had no luck.
A few days later I went out to the garage and tried again but same thing cranking but no turning over,I made sure the choke/jetting knob was "turned " all the way down , still no go.
I have since ordered a set of points and condenser that are on their way.
This Sunday is my first Model a club meeting and I am hoping someone will help me out and get it running again.
I am sure it must be something small as it was running like a sewing machine before this happned.
Does anyone here have any idea what might have happned and or what might be the problem ?
Thanks in advance ,Frank

P.S. I also changed the plugs figuring they were fouled and they were in fact black with soot but still no go and now no matter were I "set" the choke jetting knob still nothing.

Has anyone read this post a little help here would be great to at least point me in the right direction .
Thanks in Advance Frank

[johnbuckley]

Yes Frank, I've read your post. Since it's been running Ok recently it's almost certainly something simple. 95% of running faults are ignition. Clean and reset the points. 1) Ensure you have a good spark, 2) check the timing ( it may have slipped if tthe cam is not screwed tight ) 3) try fresh petrol. I find Tillotson carbs often need 1/2-1 turn GAV open , Zenith carbs 0-1/2 turn openpictures with isolating road troubles 10 mins.pdf

[fashion frank]

Thanks John .

I ordered a set of points and a condenser and hopefully this Sunday at my first model a club meeting I hope to get some help and have some body show me where I went wrong.
I think your right however and I think the points and or timing may now be off .
thanks for again assuring me as to what I was already thinking and I'll let you know how I make out.
All the Best ,Frank

[Chuck Sea/Tac]

Originally Posted by tbirdtbird

Are you using crapahol or pure gasoline?

Just everyday 10% ethanol. There must be something differènt up here in the NW, as I know Tom W. has a lot of problems as well ??

[maxandmickey]

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I had the same thing happen to me,put a new bowl and fuel line inand cleaned the carb.started right up with no more problems

[maxandmickey]

one other thing,i use gas without ethanol in it

[tbirdtbird]

can u send me some

[steve s]

Here is my brain dump from a previous thread:

Backfiring is unburned gas exploding when enough of it accumulates in the exhaust system. Anything that interferes with gas burning sufficiently in the combustion chambers will result in backfiring. There is a near infinity of possible causes, including electrical, fuel, and air issues. If this thread runs long enough, you'll hear them all.

If the problem occurs mainly under load, the cause is almost certainly electrical, i.e., inadequate spark. This is because under load, the throttle is wide open and the rpm's are reasonably low, so the engine can breathe deeply, the pressure in the combustion chamber is high making it most difficult for the spark to jump the plug gap. Make sure the ignition system is tuned and timed properly, that the coil is good, that there are not cracks or carbon tracks in the distributor cap and body, and that none of the spark plug straps are too close to the distributor body.

If the backfiring occurs mainly under idle or light load--especially at high rpm--like when roaring down a hill, decelerating, or shifting gears, the problem is probably fuel related. Paradoxically, too lean a mixture can cause accumulation of unburned gas in the exhaust system and backfiring. This is because if the mixture is too lean, the sparkplugs can't light it, so out the exhaust it goes.

What's going on when the engine is decelerating is that the throttle is closed and the engine is revving--this is a recipe for too-lean a mixture a mixture. The spark plug is trying to fire on every compression stroke, which are coming fast and furious, but the only gas being supplied is from the idle circuit, which is hopelessly inadequate for the demand. That's not enough gas to support combustion by the spark plug, so off it goes to the muffler. Do what you can to avoid high rpms with the throttle closed: don't back down in low gears and do your gear shifting at lower rpms.

Of course, if the carb is set too lean, or there is an intake vacuum leak letting too much air into the intake manifold, or if there is a fuel restriction of any sort (e.g., clogged fuel filter or jet), those all could cause too-lean mixture under normal running conditions. In all of these cases, a quick-fix straw to grasp at is to open the gas adjustment valve (on choke rod) a turn or two. If that helps, the problem is definitely fuel related, not electrical.

Another source of backfiring is a leak in the exhaust connections. This is normally a problem after shutting down the motor, whereupon fresh air is sucked into the fuel-exhaust system as it cools down. This could be either at the manifold or at the exhaust pipe clamp. If your backfiring occurs when going down the road, when there is always positive pressure in the exhaust system (unless something is really screwed up with the valves), I don't think an exhaust leak is your problem.

If the problem is intermittent and sometimes at steady highway speeds, it's probably electrical. Tighten EVERY single connection and check for possible shorts EVERYWHERE in the ignition primary and secondary circuits. You can try putting a jumper wire around the ignition switch and the ammeter (junction box lugs) to eliminate those contacts.

However, strange things can happen when rust flakes, etc. are bouncing around the float bowl. If at all possible, swap your carb, jus to be sure that's not the problem.

Steve