Continuing saga of the "Popping" Carb

[foothilltom 33]

Hey guys, I had a few hours today to continue the diagnosis on this poorly running and loudly popping 351W. Please recall my story begins with the red gas and prior to that a pretty nice running car.

 

Spent a good long time with the ignition. After repeated attempts gapping the beshitted points (yes, I swear to god I'm buying the electronic ignition soon), I finally got the Dwell Angle on the money: 39 degrees.

 

I set the timing to 6B, per the manual.

 

The popping is not as intense as before, but it's still there: once every few cycles of the engine...not ever time and doesn't seem to follow the RPMs anymore. It still pops and gets louder with RPMs, however.

 

For grins, I ran some Sea Foam at this point -- putting 1/3 down the carb, 1/3 in the gas, and 1/3 in the crank case. It smoked like the Marlboro man on a stressful day and I swear -- for just a second or two -- the popping stopped. But, ultimately it seemed to run about the same as before. I did NOT drive the old girl, just revved it in my driveway.

 

I verified the firing order again, but realized that I never really did prove where cylinder #1 is on the distributor. Had to get cleaned up to go out with the wife, so that's for tomorrow to prove the firing order is correct.

 

Just before that, I did a full compression check (on the stuck intake valve theory). Happily, every cylinder is within 1 or 2 lbs of pressure...all checking in at 140 PSI.

 

Oh, and I vaccum-checked the distributor advance. It hold a vacuum just dandy.

 

All in all, I'm wondering if I have proved anything today. If it were a valve causing the backfire, could I have equal compression like I have? I'm hoping equal compression is GOOD news.

 

To my mind, I really just have a couple of suspects left...the firing order (for tomorrow) and perhaps a carb issue. I'm thinking I could swap out the carb easy enough but I figured I'd update the brain-trust here and see if anybody has any insights.

 

Long car day. Cut my fingers once, burned my hand once. An average day.

 

Tom

[Print Dad 58]

Hello Tom,

PLease tell us the dwell angle number is a typo.

The dwell should be about 27 depending on the year.

I think you have a 351W but forget the year.

 

If it is any consolation, my car is still whislting like crazy.

Thinking of started some sort of cult band for motors.

 

Keep plugging....In my opinion you don't have internal problems.

The comp #'s verify that to me.

 

Just my 2 cents. Print Dad

[foothilltom 33]

Hey Print Dad, you're right, that was some typo. According to my book, the Dwell should be 29 degrees and that's what I set it to. It is a 351W.

 

Tom

[Pakrat 1,043]

Well, manual or not I still say 6* BTDC is just not enough timing for these cars, I'm not saying that is your problem but it should get a little more. So when you say you had "repeated attempts gapping the beshitted points" what does that mean exactly, were you still trying to gap them at the factory setting or just trying a little less/more and seeing what happens? The sea foam I am sure got rid of any remaining crud from the pink gas, thus the heavy smoke, but I still think the points need just a hair of something one way or the other.

 

BTW, did you ever try running it in the dark? Just curious if it's arcing and maybe why it seems random and not in sync instead.

[foothilltom 33]

Hey Pak, to clarify the point gap situation...

 

It took me several iterations as I kept checking my work with the Dwell meter and it reported that I was still substantially off. I was trying hard to get the points to .017" (the factory recommendation), but in order to get 29 degrees, I had to keep skoshing them closer together.

 

As you know, just turning the stupid screw changes the gap, so it took me several attempts until I got it at 29 degrees. I thought it was correct to trust the dwell meter and not necessarily the feeler gauge. I'm not saying I've done things right, but I was pleased to see 29 degrees on the dwell meter and 6B on the timing.

 

Are you suggested something like 10B? Which way would you go with it? Once I eliminate the popping, I'll be more game to tune this thing for performance.

 

And one other little observation today (though I didn't really advance my cause too much -- too many other distractions): I noted that there is an open port near my PCV valve. I think there were some 70's era smog modifications made on the vacuum lines which I was planning on removing at some point. But I think this has to mean a vacuum leak and I'll plug it when I can and get back on the horse.

 

Anywho, I'm curious to know if the Dwell meter is the ultimate authority on point gap or am I trusting that 29 degrees too much?

 

Gonna leave the US here for 10 days tomorrow, but I'll have email on the road.

 

Tom

[SlimeGold 69 15]

I'll stir this pile up too.... If you can't get the popping to stop by finding a ignition problem and from what you describe, I would be checking for a worn off cam lobe on one of the exhaust. If it sat for years and you fired it up It could have very well wiped one of the lobes off in short order. The exhaust would be finding it's way back out the intake valve when it opens. I hope I didn't just jynx you with problems like Print Dad.

Edited September 28, 2009 by SlimeGold 69

[foothilltom 33]

Hey Limey, I'm out of my depth, but would the engine report good/consistent compression in that scenario? Just looking to rule stuff in and out and this one sounds a bit bad.

 

Thanks for the info.

Tom

[SlimeGold 69 15]

It would still build compression in that cylinder. I'm not saying that's the problem but I have seen it before. Just a thought and I hope I'm wrong.

 

Also I just re-read your original post on this matter and you said it was "pinging" real bad. Was it a ping or a rocker arm raising hell? Pull your valve covers off and see if a rocker has worked loose and/or lost it's push rod. If it's on one of the exhaust valves then your popping would be explained because the valve is not opening. If all looks good, spin the motor and watch for rocker movement on all 8 cylinders.

Edited October 11, 2009 by SlimeGold 69