Thread: Kind of a Drag

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Hiya,
I got a problem now that's really kicking my can!
I'm getting a pop through the exhaust that's totally random at any time, any speed, cold or hot, night or day, sometimes loud, sometimes soft, but always VERY annoying!

Here's all I did so far;
Replaced the distributor cap and rotor.
The old center electrode looked like it caught on fire so I replace the center electrode with a low resistance one.

Replaced the coil.
I thought perhaps the electrode burning up may have caused some kind of short. Nope!

Replaced the plugs and wires.
The old plugs had a couple fouled ones and one wire was arcing on the header.
New plugs are Bosch and the wires are Taylor as I had before. I also added heat shields on 4 wires that may be too close to the headers.

Checked and reset the static timing, 10 BTDC. Checked the mechanical advance for sticking and vacumm advance for a ruptured diaphragm. Nope!

Rebuilt the 1406 Edelbrock carburetor. Made sure the accelerator pump worked. Vacumm is at 12 at 950 rpm. Normal for the cam.

Checked and re checked firing order, YES plug 5 and 7 are correct.

Checked for wire arcing at night. Nope!

Re checked the distributor cap again.

Checked valve lash on rocker arms and re adjusted just in case.

Did a nominal check for vacumm leaks Nothing obvious.

The only thing now i'm wondering is if I have too thick oil in the car. I'm running straight 50w and I don't think I had this problem before I changed oil. But from what I read 50w is good for HP since the leakdown is slow. BUT! I don't know. The lifters are not anti pump up and i'm wondering if they're not pumping up the lifters to where they leave a valve open too long.
I did notice that there's not too much oil getting to the rocker arms and the first front lifter on the right side didn't seem to have too much resistance when adjusting it but seems to work when running.
I checked the springs and they're all ok so it seems.

The only other clue I got is there's a slight whistling at the carburetor at idle that isn't always constant but mostly constant. It goes away off idle.

The popping comes mostly from the right tailpipe but it's popped through both pipes on occasion.
The exhaust does have a "T" crossover pipe. So, I don't think it's muffler baffles.

I don't think it afterburn from a rich mixture since the popping happens before engine warm up.
I didn't re jet the carb. The only change was a AN connection at the carb fuel inlet.
I checked float level and drop prior to assembling the carb.

At first after all my repairs I thought the problem went away but now it's back with a vengence.
The car has lots of power and acceleration, In fact it ran like a striped ape but the popping noises on the freeway are getting up my wick now.

Does anyone have any new suggestions? I'm stumped!

vacume leak on right side exhaust sucking in air and unburned rich mixture then igniting causing pop-

Thanks Jerry i'll check it.

Help!

I still got the exhaust popping on acceleration and it's BAD but here's the rub;
For a while I thought the problem was gone but it came back with a vengeance but the weird thing is. it went away again. The engine seems like it has power, yesterday I smoked a rude driver that wouldn't let me change lanes on the freeway. They were going 70.
Today I drove 20 miles and it did it's popping again BAD. I felt a lurch in the engine when it did it too. I drove back and it did it until I reached my hometown then it settled down. Now it's gone again.
What's throwing me off is that it's so intermittent. EVERY check has be done to ignition, timing, carb, manifolds. It starts fine, revs fine.
The only thing that's constant is that every time I take this particular trip it starts this popping in the same area and quits in the same area coming back. I'm getting to think the car is demon possessed now. It doesn't want to take this peculiar trip.

Check distributor shaft bushings, breaker plate for sloppiness, make sure the module connections are tight, and check pickup coil leads.


.

JMHO, but a couple of things come to mind.
Timing;
10* initial doesn't sound like enough for a cam that has 12" vacuum at 970 rpm. I would try 14-16* initial with 36 max. And check your vacuum advance, I would suggest you plug the vacuum off until all tuning is done, then use ported vacuum for it. And check the mechanical advance curve, you may need to adjust it. And as Mike P says above make sure your timing is steady with no worn parts.
Carbueration;
Have you read the plugs for proper jetting? This could be incorrect jetting, and check the metering circuit, the rod springs tension may need to be adjusted.

(The only thing that's constant is that every time I take this particular trip it starts this popping in the same area and quits in the same area coming back. I'm getting to think the car is demon possessed now. It doesn't want to take this peculiar trip.)

The fix seems simple to me. Change your route!

A friend had a similar thing on his old honda 750, turned out to be his condensor, though you already address this.

Mike hit exactly what came to my mind as I read your description. It sure sounds like a gremlin in the ignition. Assume it's the stock HEI unit? An all new distributor is $80 at Rock Auto. If you can't find the gremlin that's probably where I'd head, but it's a shorcut approach.

Do you have a vented gas cap?

Just adding to Jerrys 1st post sometimes the vaccum leak on the intake will seal up once the intake warms to temp and reappears when it cools down.

My impression was that you have HEI distributor.

Replace the pick up coil and capacitor.

Ignition was changed a couple years ago with a fresh MSD distributor and a MSD Street fire ignition box. Distributor mechanical advance changed with a Moroso recurve kit. Vacuum advance is adjustable. No ignition in distributor just a connection to the hall effects switch. Recently I changed plugs, new Taylor 8mm wires, cap, rotor, coil, no resistance center electrode, Rebuilt the carburetor,, changed gaskets for the base and nitrous plate, checked intake and exhaust bolts. I did not change the jetting or springs in the carb as it was fine before in fact it's at a sweet spot and checked out on the dyno. Static timing is set to 10.5 Dyno says sweet spot is 11 BTDC.
No changes were made to the adjustments except fuel filter which is now a little billet canister with one of those old style q-jet bronze filters in it. I didn't want a fuel leak on the headers. I also re adjusted the valve lash. Vacuum advance is set in the middle.

So this phenomenon has happened 3 times going from Kansas City to Gardner Kansas on I-35. By the time I get to Overland Park it starts popping just little farts. Then it crescendos to major blasts sounding like shotgun fires scaring to crap out of random drivers. Even at cruising and especially at any acceleration. At my destination even idling in park it still bangs em out only last time it was the left muffler instead of the right that was doing most of the singing. So, i start the return trip and its blasting down the freeway, bang bang bang. Then it retires to Pop Pop pop, then occasional pop, then nothing. By the time I park it's back to normal. Same trips for the same reasons. I visit my ex-pastors house but it's only to work on his cars honest! That's why I think the car got demon possessed, like Christine.
I'm sure the pops are centered in the mufflers. I do notice a slight lope in the engine but may be unrelated. The car is cold starting out both ways then gets warm. So, i'm not sure about the gaskets but at this point, I don't have a clue.
Now, I plan to check everything ignition again, any slop that may be in the timing chain and do a compression test. It's all I can think of. Beyond that all I can think to do is pull the heads. Of all the years and training I had I never ran across a problem I couldn't figure out until now. I've got to fix it. It's our only ride now. Any help I could get would be appreciated. Especially before pulling the heads. We can't afford gasket replacement.

It's the same locking gas cap I had for years. It's vented but i'll check that too.

OK, making progress, I assumed by the 12" of vacuum that you had a big cam in this motor. Now you say that when it's acting up you have a slight lope to it, now by this statement I'm assuming your motor is stock (or close to stock). So, vacuum should be much higher, more like 16-18", and with the carb whistle you probably have a vacuum leak. Check the vacuum plug caps at the the carb make sure they are all in place and good shape, and check the PCV & transmission hoses for cracks or splits.
Curious is the trip up hill one direction?