Popping exhaust??

[BigRed]

I've been really busy at work and home lately so haven't been around the site in awhile.

I have a quick question. My '86 burb has single exhaust with a glass pack. I know glass packs are supposed to be kinda poppy, but mine is doing weird stuff. When I'm at the upper point of my shift points (rpms are up) and quickly let off the gas, my exhaust has been popping really bad. Sometimes, it almost sounds like a gun shot. It hasn't always done this, just the past several months. Could it be a timing issue or is it just a warn out glass pack?

[Russell]

Mine does this too with my single muffler, it seems to be a carb related problem for me.... When I get my timing, valves and idle perfect all those sorta things disspear, unfortunately, my truck seems to have an issue with holding the valve lash properly and it slowly degrades...

[77bowtie]

After I fixed an exhaust leak, mine stopped popping like that.

[BigRed]

I could definitely use a carb tuning so you're right, that might also have something to do with it.

I don't have any exhaust leaks, so I can rule that out.

[Russell]

Yep, after I go through and time her up and reset the valve lash, I'm always so amazed by how well she runs, then within 100 km or so my number 5 exhaust valve starts ticking again, next time I'm gonna use some of the red thread lockings stuff, see if that will stand up to the oil and hold the lash properly...

My carb has never been tuned before, and probally needs a new fuel filter too, timing seems to be about correct...

[old Rusty C10]

i had one like that and we had to retard the timing a bit, but as for an exhaust leak i dont know it sounds possible. another time on an older truck it was the condensor

[BigRed]

Originally posted by ChevyGuyBC
sounds like plugs are off. check all the plugs make sure they are going to the right one on the cap. also put new plugs in..... sounds like fuel to me. carb would be last

I've checked the plugs. In fact, the plugs are new. If I had a wire crossed over, it wouldn't run as smooth as it does, right? It runs really good with the exception of this one problem. I have a feeling that the distributor is pretty old and warn. Could that be a problem? I just put in a new Ignition Module and noticed that some of the wiring harness peices (plastic) are so dried out that they are falling apart.

[crackajacka]

my 305 did that with dual exhaust and glass packs. i never found out what caused it so i had fun with it a couple of times id sit at the stop light or around town and make it pop constantly did it around 4k, my exhaust sounded like a semiautomatic gun or popcorn popping lol

[BigRed]

Originally posted by crackajacka
my 305 did that with dual exhaust and glass packs. i never found out what caused it so i had fun with it a couple of times id sit at the stop light or around town and make it pop constantly did it around 4k, my exhaust sounded like a semiautomatic gun or popcorn popping lol

Ha, ha! Yeah, it is fun. Especially when I'm on the freeway and it's about to shift into OD but not there yet. I'll let off the gas real quick and POP! I scare the crap out of people every once in awhile like that.

[Tom]

Put the vaccum advance on manifold and not ported. On ported vaccum setups, you let off the throttle and the vaccum closes and pulls timing, so the air/fuel ignites too late in the exaust. My truck will do this if I have the timing backed off too much.

[BigRed]

Originally posted by Tom
Put the vaccum advance on manifold and not ported. On ported vaccum setups, you let off the throttle and the vaccum closes and pulls timing, so the air/fuel ignites too late in the exaust. My truck will do this if I have the timing backed off too much.

That sounds like something easy to try. Now to find a good manifold vacuum source. I guess I could just splice into one with a tee right?

[crackajacka]

i had mine hooked up diffrently twice i had it off the manifold and then i had it off the full vaccum port off the carb. niether one made a difference. didnt have an smog pump(air pump) on it either

[greg0380]

From my experience, I was chasing what I thought was a backfire or exhaust leak, and it turned out to be the check valves that go inline with the AIR pump. So if you have one, check these valves, if they aren't working right they allow exhaust to go through them and sound like a backfire through the divertor.

[blink32]

Here's another easy one. How old is the glasspack? Its possible that the glass inside has been blown out or packed back into an odd situation causing some funky back pressure scenarios. If its several years old (some can blow out even faster) might as well replace it since they are fairly cheap.