1973 302 Backfiring. Can't figure out why.

[jpaz]

Looks like the terminal inside the distributer cap has turned, or it's just the camera angle is making it look that way. Look at the one that's at about 5 o'clock in your pic.

 

[Chris Womack]

Yes, it is an electronic ignition -- maybe a PerTronix.

 

[jb73Mach]

It is backfiring through the carburetor.

I checked the vacuum lines with a vacuum gauge. All plugged in, no leaks. Everything is perfect.

I checked the PCV. That was fine as well.

I checked the timing. That is also spot on.

I checked the distributor cap. No condensation.

I checked the ignition wires. They're all seated properly on the cap.

I cleaned out the carburetor with carb spray.

I'll be replacing the fuel filter once it comes in stock.

All the bolts and screws on the carb are good and tight.

How many inches of vacuum at idle?

 

[judge]

The previous writer has a good point about the cap. In looking at your pictures, I'd check the tightness of the wires on the coil, they look questionable. Also make sure you have the correct coil. Fords have a built in resistor wire that lowers the voltage during "run". Next I'd use a timing light and move the pick up clamp from plug to plug to make sure they all get the ignition pulse. Lastly I'd suspect the pickup system. But start at that cap, it just doesn't look right.

 

[72HCODE]

Ok you have electronic could be petronix.

Now the magnetic sleeve on those can go bad.

First. You can Test the vacuum advance by putting a hose on it, and suck air through it. If you suck and there is no vacuum forming then the diaphram is blown.

You can also cap the advance and go for a spin and see what happens.

To test the electronic ignition you can use your timing light place the pick up on each ignition wire one at a time and press the trigger, watch the light, the strobe should flash evenly and predictably. If the stobe is flashing intermittently on a ignition wire then you found the problem.

It can be the wire or a problem with the pickup on the electronic ignition. If that is the problem then the electronic ignition will need to be replaced...

You could also replace the coil and try again. But I think you said you replaced it.

Can it be a vaccum leak or a fuel problem, it is still possible so we try to rule out more possible causes.

 

[mrmach1]

Maybe somebody else has mentioned this or maybe you've already thought of this, but could you have a vacuum leak at the base of your carb? The gasket between the carb and the intake manifold and have checked the nuts on the base of the carb for tightness?.....Just a thought. If you lived near me I know just the Ford expert to take it to. I know he could find the cause.

 

[MikeW302]

I feel like a major *******. Took it in to the mechanic; the problem all along was the timing was waaaay out of whack (13 degrees instead of 6 degrees). I could have fixed this on my own if I hadn't been so quick to dismiss it. Oh well, live and learn. Thanks guys for all your help and recommendations!!!

 

[71mach1lady]

I guess the question I would be asking is why did the timing change if the car was just sitting? I don't know how much timing changes when the timing chain slips a tooth but if the car ran fine when you parked it and then it didn't and the timing is the reason something must have caused it to change

 

[MikeW302]

That's what confuses me. I haven;t touched the timing in three years. I set it to about 9-10 degrees to get the performance a little better. I'm wondering if over time it just crept higher up.

 

[Jeff73Mach1]

That is probably exactly what happened.

 

[jb73Mach]

Hence, my question about inches of vacuum at idle. If the timing of off, the vacuum will be low. I don't know what cam in in my Cleveland but timing with a vacuum gauge instead of a timing light works wonders for power.

 

[Cwithers]

If the timing fell that far off, you likely had the distributor gear roll pin sheared. The dist gear is a press fit to the distributor shaft and is further secured by a little roll pin. I'd hate to recall seeing how many small block fords have done this over the years. Usually happened on cold days too because the oil pump has huge load on the distributor shaft. Pull the distributor and check it. Ive seen some you could grab the rotor and twist the whole thing installed.

 

[Don C]

Interesting problem, almost any issue in the timing series of events, such as worn rubbing block on the points, jumped timing chain, failed vacuum advance diaphragm or sheared pin in the gear/shaft causes the timing to regard, not advance. My best guess is that the distributor clamp bolt wasn't tight enough and you bumped the vacuum advance at some point, advancing the timing.

 

[72HCODE]

just to throw more fuel on the fire...

I've seen garbage aftermarket ignition wires cause timing to fluctuate in different weather. all those made in china 8mm,9mm,10mm spiral core ignition wires should be banned from sale.

that said,,,, besides the distributor gear as a possible problem. you could have a bad harmonic balancer with the timing marks on it. the timing marks can move around because it separated from the rubber isolator and you cannot set the initial timing because the timing mark will keep changing as the engine runs so you will keep correcting it with the strobe light thinking the engine timing keeps changing when it is not the mark that you measure the timing from is changing.

could also be a loose bolt on the distributor hold down, when you rev the engine the distributor base can spin advancing timing.