Exhaust popping at idle

[bobbyg63]

Okay guys, I need a little help. I've got a 63 fuelie and it actually runs great. My problem is that when it idles, it has a noticable popping sound from the exhaust. The engine is in time and idles smoothly, can anyone out their tell me whats causing this popping sound? Is it a serious problem or should I just forget about it.

 

[Chas]

i would check for a small hole in your exhaust system...could be size of a dime or so...if you dont hear it from the engine but its out the exhaust , i would think its puffing out or in from a small exhaust leak...

Just my opinion bud.
Chas

Okay guys, I need a little help. I've got a 63 fuelie and it actually runs great. My problem is that when it idles, it has a noticable popping sound from the exhaust. The engine is in time and idles smoothly, can anyone out their tell me whats causing this popping sound? Is it a serious problem or should I just forget about it.

 

[WayneC]

One possibility I can think of is a valve out of adjustment.
Or perhaps the FI is idle mixture is a little too lean.

 

[Vette66AirCoupe]

Check your connection at the exhaust manifold and the exhaust pipe. Those nuts have a tendency to loosen. There's a donut in there that sits on the flanged exhaust pipe that can erode too. Is it more noticeable while warming up?

 

[WayneC]

Good point, Terry, I assumed he meant it was popping at the tailpipe... but maybe he didn't mean that, so it could just be a leak between the head and the manifold at one of the exhaust ports.

 

[bobbyg63]

Thanks guys, I'll check them all. I did mean popping at the exhaust tips. If it turns out to be a lean mixture, and not an exhaust leak, which I don,t think it is, how does one properly adjust the Idle mixture screw on the fuel unit. Seems like when I start to adjust it like the manual says, to get the best idle, the engine starts to run rough, so I shut it down then restart it and it seams to idle better, but the popping sound is still their. Which way on the screw richens the mixture? Is their a way to tell when its right or is it just how well it idles?

 

[Ron Miller]

Okay guys, I need a little help. I've got a 63 fuelie and it actually runs great. My problem is that when it idles, it has a noticable popping sound from the exhaust. The engine is in time and idles smoothly, can anyone out their tell me whats causing this popping sound? Is it a serious problem or should I just forget about it.

Not sure exactly what type of "popping" sound it is making, is it at both exhausts, or only one? It's possible it could be a burned valve, more likely if it's only at one exhaust pipe, since I wouldn't normally expect to have a burned valve show up at once on both sides of the engine. Can be caused by not enough clearance in setting the lifters on a mechanical cam. But, the sound is not exactly a popping one, more of a "thip, thip, thip" type of sound. (Forgive my feeble attempt at trying to explain the noise, you have to have heard one to know exactly what I'm trying to express. An experienced mechanic will usually know).

 

[andy60]

Try the old dollar bill trick

The old dollar bill trick is:
Hold a dollar over the exhaust, if it sucks it back against the tail pipe then you may have a valve hanging or a little open for some reasion. If the bill does not suck back it is an issue other than valves.

It works. A used car dealer showed me that trick 30+ years ago.

 

[BLACK MOON]

Good trick. A burnt valve will usually suck and rip the bill. I've shown others that trick and they think I'm crazy. I am a bit crazy but the trick works.

 

[JohnZ]

Do you mean "popping" like a backfire, or just loud exhaust pulses? Exactly under what conditions does it "pop"? In any event, it's highly unlikely that it has anything to do with the F.I. unit; most "fuel injection problems" turn out to be ignition-related, and you don't want to start fiddling with the fuel adjustments without special tools and knowledge or you'll have other problems. Run the basics on the ignition system first (dwell, timing, centrifugal and vacuum advance, points, condenser, rotor, cap tracking, wire routing and condition, spark plugs, etc.), check valve lash, exhaust manifold-to-head bolts, exhaust flange nuts, pipe joints, etc.

 

[bobbyg63]

john,

Thanks for the comments. The popping occurs only at idle is not loud, but you can hear it through the exhaust rumble at each pipe. The car accellerates fine with no missing. I did install new 1.6 rockers and readjusted the lifters to specification twice. If I did get a valve setting slightly tighter then its specification, would this be the reason for the poping? I've checked for leaks in the exhaust system, found none. I put a dollar bill at each exhaust tip and it blows it away and does not suck it in. I guess I'll just live with it. Thanks

 

[JohnZ]

"Popping" as you describe it isn't normal; you shouldn't have that condition unless you have an exhaust valve that isn't closing fully. What procedure did you use to lash the valves?

 

[c5vetter]

Check to make sure you don't have any wires crossed! Had that problem with my FI last week coming out of restoration!

 

[bobbyg63]

john,

you were right on, I reset the valves using the technique where you adjust 2 valves and rotate the crank 90 degs each time until you adjust each valve. I found 2 exhaust valves much too tight. After reajusting them twice while hot, I restarted the engine, and wha-la, no popping sound, just a nice, smooth running engine. Thanks a lot. This forum is great for solving problems.