Exhaust Popping

[Stumper]

What would cause popping (mini explosions) in the exhaust? Started my car up this morning and out of the blue is was doing it. A year or so back I had the same thing happen one day when I started it up. Can't remember what I did to make it go away - plugs maybe??

 

[detmatt1]

Sounds like a timing issue to me unless you are somehow getting unburned fuel into the exhaust manifolds where it is igniting from the next exhaust discharge. The popping sound is more likely the sound of cumbustion through an open exhaust valve. Check your vacuum advance or for any other vacuum leaks while your at it. These are just guesses as I am no engine specialist by any means.

 

[Stumper]

No vacuum advance on this, it's all mechanical.

 

[detmatt1]

Ah, good man!

 

[Garys1969RR]

That sounds like unburned air/fuel mix going thru the engine, then igniting in the ex pipes, as detmatt said. What cam are you using? Long duration/overlap profiles would tend to agrravate the condition. Also poor spark plug wires or carboned up plugs would make it worse. A guy in high school used to hold his throttle wide open on his 52 Ford, then shut off the key. As the engine continued to spin down, it would fill the pipes full of unburned fuel air mix. Then when he turned the key on, it would explode. Sounded like an M 80 goin off. He did it one too many times and blew up the muffler. True story!

 

[dryheat]

That sounds like unburned air/fuel mix going thru the engine, then igniting in the ex pipes, as detmatt said. What cam are you using? Long duration/overlap profiles would tend to agrravate the condition. Also poor spark plug wires or carboned up plugs would make it worse. A guy in high school used to hold his throttle wide open on his 52 Ford, then shut off the key. As the engine continued to spin down, it would fill the pipes full of unburned fuel air mix. Then when he turned the key on, it would explode. Sounded like an M 80 goin off. He did it one too many times and blew up the muffler. True story!

I used to do this too ... till I broke an exhaust valve and ruined the engine.

I agree with the previous posters about un-burned fuel entering the exhaust system.

 

[Stumper]

No doubt the pops are (were) coming from fuel burning after the chamber. The bigger question was why - but I think it was plugs - for now at least. I just stuck in a set of clean old ones and the popping stopped. I think the problem goes back to me running so rich and fouling plugs in the first place.I've tried several main jet and power valve changes in this carb with screw adjustments and just can not get it to lean out. May need to get someone who knows these carbs better play with the air jets?

 

[tpodwdog]

unburned fuel getting in the exhaust system indicates a fouled plug or a misfire...check and make sure all the plug wires are on tightly...on both the distributor and the plugs...and make sure theyre in good shape and not burnt and grounding out someplace. perhaps a sticking exhaust valve.

back in the day we used to hold open the throttle and pour water in the carb to clean out combustion chambers and carbon .

 

[MoparMuscleGuy]

Check to see if one of your plug wires is burned and touching the header. MMG

 

[1962savoy]

I had the same problem fouled plugs! Those Dominator carbs are pig fat and hard to tune

 

[67 coronet]

what carb are you running,and what is vacuum at idle.

 

[Stumper]

I run an HP 950. Vacuum at idle (1400 rpm) is about 4-5"

 

[63 Savoy]

popping

if the carb is fat at idle--could be not enough air past the transfer slots--if this is the case you can drill each of the throttle plates .125 hole and set transfer slot to about .025 on the front and back--re-instal and set idle speed and then mixture screws--this has always worked on my dom. , nice clean plugs--hope this helps--maybe you have already done this--Mike