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misfire popping sound through exhaust help with plugs

80K views 55 replies 13 participants last post by  tomwadek 
#1 ·
Hey guys my misfire is back again. I'm getting the same constant popping sound through both exhausts at an idle. I pulled the plugs which are a month old and this is what they look like. I think I'm running too lean? The thing is, it smells like gas and just standing behind the car makes your eyes water? What can you guys say about the plugs?

Things i've done:

New wires( one month old msd)

New cap and rotor

Did a valve adjustment and it checked out great.

It's always been misfiring, engine barely has 600 miles on it.

Carb was way too lean when I first got the engine back ( was backfiring through the carb on acceleration, I went up two jet sizes and it went away but car seems like it still doesn't have that power... feels like it wants more gas but I dont know if it's too lean or rich cause it smells like gas and I have that popping sound at the exhaust like it's missing)

am i too lean or rich?
 

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#3 ·
If you have remote temperature gun , shoot each tube on the headers and see which tube or tubes are running colder , those would be the cylinders to look at . If you don't have a gun, spray water from a bottle on each header see which ones the water don't boil of quickly and look closely at those cylinders . Check the plugs and wires . Check resistance across the plug wires , if you have a meter . Swap the plugs around and see if the problem moves to another cylinder with the plugs , then you'll know it's the plugs .Good luck
 
#6 ·
Check that you are getting spark to all cylinders. Popping through the exhaust could either be raw fuel loading up in your exhaust (more like a boom), or a lean miss. One plug or more will be wet if this is happening.

If you're all good there, I would go up a couple more primary jet sizes and see if it gets any better.
 
#7 ·
well theres no loud boom just a constant light popping that can only be heard standing at the back of the car. All header tube are 172 degrees and a spark plug tester shows all spark plugs are going off.

If it's too lean why does it smell so rich?
 
#9 ·
well I just took it to a carb shop and i had him hear the exhaust and showed him the plugs. He test drove it and said based on everything I'm wayy too lean. The car wants to get up and go but isn't getting enough fuel...

He's charging me 150 to set it up right. hopefully this works...
 
#11 ·
Popping through the exhaust is usually a lean condition which causes an over-heated exhaust.

Most the time, it's a vacuum leak,..which is un-metered air getting to the combustion chamber. With a trained ear, sometimes you can hear the vacuum leak. Otherwise, check each of the vacuum sources, check for the correct carb mount gasket, and check for a leak at the intake manifold.

Also, if your timing doesn't have enough lead, she'll burn warm which will elevate the exhaust temps.

Good luck!
 
#12 ·
ok just got it back. He had to go up a jet size and it's not missing anymore, the rpms aren't jumping and I dont feel it anymore, however; I do still hear the popping in the exhaust at idle but it's sooo faint. I hear it more often in the passenger side exhaust but again it's faint. He said it's because there is still some unburnt fuel sitting in there and it should go away on it's own. Any truth to that? or should I ask him to make it more rich. Car feel responsive now...
 
#13 ·
I hope your carb guy checked for a ruptured power valve, a fairly common problem when it backfires through the carb. You may still have a vacuum leak, check torque on intake bolts and make sure your carb gasket is sealing properly to the intake.

Searching for vacuum leaks can be frustrating, here's my method: Get a can of Gumout choke & carb cleaner and spray any spot you suspect a leak while idling the engine. If idle speed goes up when you spray a spot, you've found your leak.

Your plug gaps look really wide, have you set them to the spec for the ignition system you have?
 
#15 ·
heres an update. I did the carb spray thing to check for vacuum leaks and found nothing. I did this at a low idle but the rpm didn't change at all.

The car is no longer burning my eyes if I stand behind it. The right side tail pipe(passenger) has a very very faint popping. The driver side does not anymore.
 
#16 ·
tomwadek, I had the exact problem. It turn out to be the same plug I was using. Replace it with Autolite plugs for street driving. Stay away from Accel plugs. They are made for racing.
 
#19 ·
I had just redone the exhaust because I put some new headers. The old headers I had hung too low and blocked the oil filter so they had to go. This popping problem was there before and after the exhaust work.

Making the car richer solved 90% of my problems. Do you guys think it needs to be a little bit more rich?

The kit I bought with the jet sizes and springs from edelbrock, couldn't go any larger according to the carb guy.

He told me it would go away in a day or two because the fuel was most likely still trapped in the exhaust system. He was right about the driver side it did go away but the passenger is still faint.

The car doesn't "Miss" anymore. It feels good and rpm and oil pressure needles are not bouncing like before. Also, when it did miss it was felt! everyone in the car would be like, " that's a bad miss." Just putting your hand on the fender you could really feel it. Not anymore.

I'm just asking if it's stuck fuel in the exhaust and if I should wait it out or try to take it to another carb guy to go a little bit more rich. Thanksgiving is coming and I want to be able to enjoy it on that day...

I could also try to change the plugs again. maybe they got really fouled these last week???

More info on my set up:

454 bore .40
280 comp cam
hei set up
edelbrock 1489 kit for the 1411 carb( which came lean from factory)
 
#23 · (Edited)
Sorry I can't give that info. I can't remember what it was. My Chevelle is getting a new paint job at a body shop. It's a been awhile I pull the plugs out.:D
BTW: Thanks on the comment on the video.
 
#27 ·
Well, if this is your carb - http://www.edelbrock.com/automotive_new/mc/carbs_acc/pdf/carb_owners_manual.pdf

The manual shows where and how the circuits work. Not sure how much carb experience you have, but you can see that air and fuel travel through different places on the carb.

I think drilling or changing the tubes are your methods of tuning the idle circuit...

See if that helps out.
 
#33 ·
ok, still getting popping only from the right exhaust... Now the rpm needle jumps and I do have a miss but it's slight... I'm changing the accel plugs tomorrow and going with the autolite shorties...

If it still does it then i need to make it more rich some how.
 
#35 ·
I have timing locked at 18 initial( it's a 280 comp cam). guy at a performance shop said it needs more timing? Does that really cause a miss?

I bought the new plugs but haven't had a chance to put them in cause of the Holiday. I ended up buying the ac delcos r44t


one more thing, In the summer I upgraded my cooling system and the car ran in 100 degree heat at 180 at cruise and 185 at idle which is great .

Now that's it's a little colder she runs at a cruise at 170 and an idle 172-3

Is that too cold?
 
#36 ·
i just changed out the plugs. It doesn't have a miss anymore but I dont like how the old plugs on the passenger side looked at all. The driver side was getting there but not as bad. I dont know how to read spark plugs so I dont know what it is telling me. Can you guys take a look and see?

All 4 on the passenger side looked like this and these are the old plugs before tuning the carb and making it rich.
 

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#37 ·
Drove it around and now the popping is back but on the driver side. It's not missing anymore but it's popping.

I also noticed if I play with the idle screws my operating temp will go up to 192 if I make it rich and goes down to 178 if I lean it out..

What the heck is going on!
 
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