General Tech Backfiring

[Crisis]

I posted this question on the Jaguar Forum. I also have a TR6 and am familiar with this forum so I thought I would post here as well. This problem could no doubt occur on either car.

"Dear Members,
I have had a 1965 E-type for 2 years now and have encountered a new problem that I am looking for help with.

I took the car for a spin yesterday for the first time since last fall. Initially it ran fine. Started ok, idled ok, drove ok for a short 10 minute test. Then I thought I'd take it out for a little longer and strange things started happening. It started to backfire (very loud from muffler) at low speed, wanted to die at idle, hard to accelerate and would backfire more. Once I was up to speed it would be fine but then approaching a stop I could tell it was going to stall and when I give it some gas to keep revs up it would backfire again. No water or moisture anywhere, and it was a warm but not hot day (75*).
Some history, at least what I know:
-I just replace the muffler. This is why I didn't have the car on the road till now. Seemed to go ok. Could be a slight leak but I haven't had on a hoist to give proper inspection.
-Just prior to my purchase, PO put previously used points and condenser back in distributor so he could give his buddy the Pertronix Ignitor module he had been using. He then included a new Ignitor with the car but not installed (still not installed).
-Everything "looks" ok under the hood. Carbs not wet, fuel filter bowl looks clean, no visible signs of anything wrong around intake.
Any advice would be appreciated. Beautiful fall weather and I'd like to put some miles (finally) on this car. Kinda embarrassing the way it is.
Thank you,
Reid'

 

[Darrell_Walker]

I had similar symptoms on my TR8 when the timing was overly retarded.

 

[TuffTR250]

How old is the gasoline? If it is ethanol, that could be the problem. But after checking the gas, I would start with the ignition system, check points and their adjustment, check timing, check how the spark plugs look, are they sooty black, white, or normal.
Regards,
Bob

 

[CJD]

Yep...exhaust backfiring is always ignition.

 

[Geo Hahn]

Yep...exhaust backfiring is always ignition.

Except when it is lean running (typically occurs on deceleration). Certainly points and timing are the place to start.

 

[tomshobby]

Backfiring means there is combustion in the intake manifold.
Could be several things including intake valves leaking. Exhaust valves not opening enough to evacuate the cylinders, usually means a worn cam lobe. Could also be electrical causing spark when one or more cylinders fire while the intake valves are not fully closed.
Being that it ran good when it was parked and you did not change anything before you starting driving it again I would suspect the cap and rotor.

 

[TR3driver]

Backfiring means there is combustion in the intake manifold.

The term "backfire" means different things to different people. Many (including myself) use it to include combustion in the exhaust system. Eg,
"1. An explosion of prematurely ignited fuel or of unburned exhaust gases in an internal-combustion engine."
https://www.thefreedictionary.com/backfire

 

[CJD]

Except when it is lean running (typically occurs on deceleration). Certainly points and timing are the place to start.

That is very lean backfiring, and only under severe overrun. The weak mixture under overrun is not normally damaging. More of a "pop, pop, pop sound. A loud backfire is more of a "bang" or "boom"! In general, loud exhaust backfiring is always ignition.

On the bad side, exhaust backfires usually destroy the muffler. You will be lucky if your new muffler survived.

 

[sp53]

Ignition like John suggested, and I view it the same as Randall. In your case, if it is laud right in the muffler, I would suspect a make and then break in the ignition circuit. Kinda like when we were kids and turned the key off and then back on to ignite the gas vapors in the muffler. I would look at a loose coil lead or maybe the coil itself cutting in and out.

 

[Born_Loser]

-Just prior to my purchase, PO put previously used points and condenser back in distributor

I would fully expect that to be the problem in this description....Of course it could be a lot of things...but Occam's Razor says thats it. Of course, Occam never had a British car...

 

[poolboy]

What carbs are on this engine ?
If ZS, have you checked the condition of the air valve diaphragms ?

 

[Marvin Gruber]

C posted in the jaguar forum that the gas was a year old. Need I say more.

Marv

 

[pdplot]

Water in the gas? Unusual, but so is backfiring. Usual cause is cessation of ignition - like turning off the key and then back on again. BANG! A bad condenser might cause the problem as well. They're cheap so replace it and see what happens.

 

[Born_Loser]

Water in the gas?

Probably chunks of Ethanol slime. Although ignition would STILL be my number one candidate, a buddy of mines motorcycle (side draft carbs) had this problem from the dreaded ethanol slime - sat too long. Good news was, it cleaned up for the price of a gasket kit, and an afternoon of telling lies.

 

[TR3driver]

That is very lean backfiring, and only under severe overrun. The weak mixture under overrun is not normally damaging. More of a "pop, pop, pop sound. A loud backfire is more of a "bang" or "boom"! In general, loud exhaust backfiring is always ignition.

Used to get it frequently with my old motorhome. Compression braking down a long hill after heavy load climbing the other side. The engine was basically not running at all, just pumping weak fuel/air into the exhaust system. No gulp valve on that engine and the power valve was in the full lean position (due to high manifold vacuum). Not sure what set it off, and it didn't always happen, but every once in awhile BANG. I literally thought someone was shooting at me the first time! And I had other drivers tell me about the flames shooting out the (side) exhaust.

Never seemed to hurt the muffler either, but it was a great big low restriction truck thing. Dunno what an E-type uses, but the stock TR3 muffler is a straight-through glasspack that isn't likely to be damaged by a backfire. Which is good, because the TR3 does a lot of popping as well. Maybe new exhaust valves will help.

 

[CJD]

Ignition like John suggested, and I view it the same as Randall. In your case, if it is laud right in the muffler, I would suspect a make and then break in the ignition circuit. Kinda like when we were kids and turned the key off and then back on to ignite the gas vapors in the muffler. I would look at a loose coil lead or maybe the coil itself cutting in and out.

You brought back some old memories, Steve. I had totally forgotten my old man showing me the backfire trick with the key!

Water in the gas is not helping the running. Also, I would assume if the points were swapped out to begin with, there was likely a reason! I think a new set of points and condenser would be a good first step.

 

[Crisis]

Thank you all. I'm going to install a new Ignitor in the distributor tonight and see if that solves the problem. Previous owner had included one with the car I just haven't installed. Will let you know.
Reid

 

[Crisis]

Leads to another question (never quite as simple as it says on box). Pertronix Ignitor has two leads coming from it; one for positive post on coil, one for negative post on coil. I gather the negative wire goes straight to the post, but the positive wire will need to be spliced in with the ignition wire that also goes to the coil? Not in front of the car right now so am trying to understand this from memory. Anyone else installed this Ignitor?

 

[Darrell_Walker]

The positive lead doesn't really need to connect to the positive post on the coil, that is just a convenient place to pickup ignition-switched power. Depending on what type of connections you have on the coil, you can either just add ring terminal to the Pertronix and add it, or if it is spade-type connectors they are adapters with more than one spade.

 

[poolboy]

When I had the Pertronix Ignitor, this is how I had it connected to the coil.
I shortened the wires and changed the size of the connectors to fit the spades on the coil.