'62 Backfiring

[Paul Giganti]

My '62 has started backfiring. First it was a little, now it's a lot. It backfires off and on while idling and when running at even throttle. It doesn't seem to backfire on acceleration. I seems to be coming from the exhaust, not the engine bay. From what I've read it sounds like I might have an exhaust leak (though I'm open to other opinions).

If the cause of the problem is most likely an exhaust leak, I'm unsure how to tighten things up. I had a look under the car today and all I could see and/or reach was one exhaust bolt on each side—out of what I assume are four exhaust bolts or nuts on each side.

Is there some trick to getting access to ALL the exhaust bolts/nuts without having to drop the engine? I'm limited to a jack and stands; I do not have a lift.

Love advice on this.

[Martin Benade]

If it backfires at idle and even throttle it may be something other than exhaust leaks. Try looking in the engine compartment with it running in the dark. See if you see any sparks jumping between plug wires or across the distributer cap. Also inspect the inside of the cap for carbon tracks or even dirt (engine off). Still could be exhaust leaks too. If things are getting rusty, either holes in the muffler, or leaks developing where the J-pipes connect to the lower muffler inlets.

[Mike Wilson]

I'd check for a clogged idle jet/circuit. I know there is probably a thread on checking to see which cylinder is involved.

Mike

[Ron LaDow]

Backfiring thought the carb means 'lean', through the muffler means 'rich'. Backfiring on overrun means an exhaust leak somewhere. Pretty much always.
Regardless, do a tune up to make sure you don't have a tight intake valve or really screwed ignition timing. And it will make your engine run better, I promise.

[David Jones]

Get a stethoscope or even just a flex tube you can stick in your ear then put the end close to where there is a likelihood of a leak. Makes it real easy to find, very noticeable when you get close. The cheap parts store stethoscopes work well. I use a piece of 1/4" copper tube stuck in the business end to use as a wand to hunt down leaks.

[Martin Benade]

A piece of fuel hose is more comfortable in the ear than copper tubing.

[David Jones]

I use soft copper tubing Martin.

[Harlan Halsey]

Paul,
You get access to the exhaust studs by removing the rear engine shroud. Then you can tighten them all from above. A short box wench helps.

[Martin Benade]

I think Ron's causes of different types of backfiring is your beginning point, ahead of my suggestion as well.

[Paul Giganti]

Get a stethoscope or even just a flex tube you can stick in your ear then put the end close to where there is a likelihood of a leak. Makes it real easy to find, very noticeable when you get close. The cheap parts store stethoscopes work well. I use a piece of 1/4" copper tube stuck in the business end to use as a wand to hunt down leaks.

I do have a stethoscope, but I'm not sure where one the exhaust to inspect or what to listen for since I can hear the backfires without one. Do I listen at the attachment to the head and what do I listen for? If I have a hole somewhere in the muffler or headers, how would I find that other than by sight?

[Mike Wilson]

I'd check where the muffler attaches to the heads, both J-pipe attachment points (front and rear) and S-pipe connections. If leaking, you should be able to not only hear but see evidence of "flaming"; dark smudges at the leaks.

First, I'd follow Ron and Martin's suggestions.

Mike

[David Jones]

Paul. be sure and use just the tube of the stethoscope when listening for a leak as using the sound amplifier box will not work.

[Dave Wildrick]

Here's a blast from the past from "Maestro" Harry Pellow on how to find exhaust leaks. I have used this method with success to find J-tube leaks.

[Date: Sat, 13 Nov 1999 23:56:35 -0800 (PST)
From: Harry Pellow <maestro@mail.well.com>

Here's another test that will pick up even pinhole leaks:

To find where an Exhaust Leak is coming from (Some Exhaust leaks sound
EXACTLY like Rod Knock!), try this (takes 2 people, or very long arms).

While YOU are under the engine shining a Strong Flashlight up
at one particular Cylinder/Head Junction or "J" tube/head Junction (Easy
with Euro Heaters. Harder, but possible with Double Flapper Heater Boxes.
Difficult with Single Flapper Heater Boxes), an assistant drops a couple of
'cc's of TWO-STROKE MOTORCYCLE OIL ('cause it burns clean), down the throat
of the carb of THAT PARTICULAR CYLINDER you're eyeballing.

If there is ANY pinhole leak at any junction, copious quantities of White
Smoke will bellow forth therefrom forthwith.

Repeat this test, eyeballing the Head/J Tube connection of
that cylinder. Again a Great Blast of white smoke will come out of the
Head/J-Tube junction if there's a leak present.

Repeat these tests on the other three cylinders.
A blown-out exhaust gasket is very commomn these days, thanks
to those damned non-asbestos exhaust gaskets in all the current gasket
sets. And like I said, a badly blown exhaust gasket sounds just like Rod
Knock. So does a leaking Head!


Keep the 356 Faith
Maestro]

[WilliamVaughan]

If an idle jet gets clogged such that the throttle-closed mixture for that cylinder is too lean to burn in the cylinder where it is supposed to burn, then the unburnt fuel can accumulate in the muffler until it eventually ignites with bang. (and blows off an expensive tail pipe on a crowded expressway)

A good reason not to set the idle mixtures at lean-miss or the very top of the RPM peak.
Better to set them toward the rich side to allow for the leaning that occurs when engine braking on a down slope.

Poorly sync'd Solexes can cause farting.
Old fuel can cause farting.

[Mike Wilson]

"Old fuel can cause farting." So THAT'S my problem! Ha!

Mike