Ignition backfire

[brendan.hoban]

My car is a RHD 22 touring, no starter or generator.

I hand crank three turns on full choke.

I then crank on battery and, almost every time it backfires through the carburettor.

On the rare occasions I can get it started, it runs well!

Here is what i have done.

1. Removed, cleaned, regapped and reinstalled the plugs.
2. Replaced the spark plug wires with new.
3. Removed the coil box (plastic walled) checked all coils, found no carbon tracks, all coils firing properly.
4. Removed the Tiger timer and replaced it with a known Anderson flapper.
5. Checked the wiring loom and can find no faults or shorts.

Where do I go from here? Any advice would be appreciated.

[bobt]

Did you reset the timing after replacing the timer? bobt

[Humblej]

I agree with Robert, it is probably the timing. All timers are different, so changing the timer requires re-timing. Ford had a gage to set the timing, but that only works for a Ford timer and Ford roller.

To set the timing, take the #1 spark plug out, hand crank slowly to find where the plug fires, it will only fire once in 2 revolutions. Use a length of wire to go thru the spark plug hole and rest on the piston. The piston is not directly under the spark plug so you will have to angle it. Crank the engine over and the wire will go up and down with the piston, crank until you find top dead center, then go just past TDC and that is where the spark plug should fire when the spark lever is fully retarded. To adjust the timing, bend the timer rod to lengthen or shorten to make it fire sooner or later.

Warning, an out of time ignition, one that fires early, may cause the engine to momentarily run backwards during start up, this is a dangerous situation that could cause serious injury while hand cranking or damage a bendix during electric starter starts.

[J1MGOLDEN]

A friend took his coil box out to rebuild it and put it back in with the #1 coil wire going to the #4 spark plug.

The #1 coil is still on your left when looking at it from the front.

Getting those wires mixed up and the Timer to Coil Box wires mixed up is very easy to do.

The #1 Timer Terminal is still on your top left when looking from the front, followed by #2 below and #4 across.

Then, sometimes the camshaft hole drilled for that short nail pin is drilled all the way through and allows the roller to be installed 180 degrees out of time.

[Bill Robinson]

Just getting basic here, sorry, but did you wire the timer in the correct firing order, which is 1-2-4-3? If not, you'll probably get a backfire- maybe 2.

[Moxie26]

What brand / style of spark plugs are in the engine? It seems that the newer one piece Champion plugs have a continuity problem between the top terminal and the center electrode, sometimes they work sometimes they don't it could be from corrosion between the center electrode and the connector on top and/or over tightening the terminal giving those problems. Just simply check with an OHM meter the continuity between the terminal and the central electrode on the plug.... Some resistance or no reading at all is your culprit.

[AndreFordT]

I am with Bobt.
You will need to set up the timing right.
Pay attention when connecting the wires. On the RHD cars the timer is mounted up side down.

Good luck
Andre
Belgium

[Norman Kling]

I agree with the above posts. The reason for your backfire is that it is firing when the intake valve is open. Timing is the usual cause of this problem. It could also be caused by a leaky valve. There is fire going out the intake manifold and when it reaches fuel inside the manifold it spits fire.
Norm

[speedytinc]

My car is a RHD 22 touring, no starter or generator.

I hand crank three turns on full choke.

I then crank on battery and, almost every time it backfires through the carburettor.

On the rare occasions I can get it started, it runs well!

Here is what i have done.

1. Removed, cleaned, regapped and reinstalled the plugs.
2. Replaced the spark plug wires with new.
3. Removed the coil box (plastic walled) checked all coils, found no carbon tracks, all coils firing properly.
4. Removed the Tiger timer and replaced it with a known Anderson flapper.
5. Checked the wiring loom and can find no faults or shorts.

Where do I go from here? Any advice would be appreciated.

The thing that comes to mind is the pan mounting bolt directly under the timer. The bolt should be mounted backwards, meaning thread down. If mounted up like the rest of the pan bolts it can contact 1 timer terminal.

Did this issue exist with the other timer?

[TXGOAT2]

"On the rare occasions I can get it started, it runs well!"

I would try to determine which cylinder is producing the backfire at the carburetor. That can be done by removing and grounding one spark plug wire at a time, then trying to start the car as you usually do. One of the four is probably causing the backfire, and disabling it will allow you to concentrate on finding the issue. If it's not an ignition issue, it could be a weak intake valve spring, sticky valve, or a valve adjusted too tight. It's odd that it backfires on starting, then runs well once started. It could be nothing more than a weak mixture, and if so, opening the carburetor adjustment a little more and choking it a little more may be all that's needed. In most cases, any set starting procedure will need some modification to suit conditions of the moment.

[Craig Leach]

Hi Brendan,
Lets throw something on the wall and see if it sticks. You said it runs well when it starts? The reason a engine runs hot with a lean mixture is
that a lean mixture burns very slow and exposes the cylinder wall to the flame longer. With this in mind if the mixture is to lean there can be
flame still in the cylinder when the valve opens causing the air/fuel mixture to ignite & pop out the carb. The same as firing the plug when
the valve is open or having a leaking valve will. Try opening the mixture screw 1/2 turn & choking 5 pulls just to see. look for a drop or two
of gas at the inlet of the carb. The worst that can happen is the engine gets flooded and will not start, if it still backfires you should have
eliminated the lean mixture as the issue.
Craig.

[brendan.hoban]

It's still backfiring.

In addition to my previous post i have,

1. Pulled out the ingition loom checked everything, repaired a small defect with two layers of heat shrink and reinstalled it,
2. Checked the firing order, its all OK,
3. Pulled off the valve spring chamber cover and found all valves going up and down as they should,
4. Slightly enriched the mixture,

and it still backfires through the carburettor!

I think it might be happening on No. 1 cylinder.

I'm reluctant to pull the head as I have no more new head gaskets so I'll try to view No. 1 inlet valve through the plug hole.

Any more suggestions?

[Kaiser]

I suspect a fuel problem, all symptoms of a backfire from too lean a mixture, maybe a warped manifold or broken gasket,
As a simple way to check for a leaking valve, with the valve cover off check to see if both valves of one cylinder are closed, then remove sparkplug and put air hose in hole, listen for a hiss in inlet manifold or carb, repeat for all cylinders.
This way you can ascertain it is not a sticky or leaking valve.
Good luck

[dykker5502]

Anderson timers fires at different places as the roler timers.

You still ough us to tell that you checked and eventual adjusted (by bending the rod) the timing.

[TXGOAT2]

Open the carburetor adjustment to 1 full turn off the seat, then, with ignition off, hold the choke out all the way and crank the engine until it floods. (4 to 8 quarter turns against compression) Then release the choke, turn on the ignition, and crank the engine (quarter turns against compression) until it starts. You may need to move the spark lever 2 to 4 notches down from full retard. (Do this with caution, observing safe cranking procedure!)

If you get it started, be sure to turn the carburetor adjustment back to its normal running position, about 7/8 of a turn off the seat, once the engine has run for 30 seconds to a minute. Also advance timing about halfway down the quadrant as soon as possible after the engine starts. I get good results when starting with the throttle lever about 1/4 of the way down. or just a little more. If starting on MAG, it's often helpful to move the spark lever down 4 to 6 notches down from full retard. (Use caution!)

If you continue to get a backfire at the carburetor when starting on a rich mixture, it points to an ignition or valve issue. A pop at the exhaust on starting can point to a lean mixture, ignition issue, or valve issue.

A minor intake gasket leak can cause cold starting issues, as can a worn throttle shaft or loose throttle plate.

[TXGOAT2]

As Kaiser pointed out, you can easily check valve seating without pulling the head. If you are using heavy, straight grade oil, replacing it with a multi-grade oil, such as 10W30, will ease starting.

[Moxie26]

Brendan..... Just do the cheapest..... install new spark plugs,set gap at .025" . tighten plug terminal by hand.

[Scott_Conger]

First, a car which sometimes fires back through the intake but runs well may well have a sticking-open valve and you'll never see it in the valve chamber...it will go up/down but may not be seating (I am not saying this is your case). Second, just because you do not have a headgasket does not mean you cannot inspect for this problem

Simply bring each cylinder in turn, to TDC where all both valves SHOULD be closed and apply a bit of air through a fitting made to fit the spark plug hole. If you hear a bit of air escaping past the rings, in the oil filler, well, that will be normal, but you should NOT hear air coming from the carb or the muffler. This is how you test for valve sealing. If you have a bit of a burned valve or a tiny hang-up on the intake, there will be no mistaking it when you listen at the carb.

now that I typed all this, I see that Leo told you the same thing...he's right

[Jerry VanOoteghem]

Your first piece of advice was to check the timing. Did you do that?

[TXGOAT2]

Toi test valve seating: Bring each cylinder, one at a time, to TDC on the compression stroke , then apply air pressure to each one,, and listen for escaping air a the carburetor and exhaust. Have throttle open. Escaping air can be clearly heard at muffler outlet or carburetor Caution: Compressed air can cause engine to rotate. After bringing a cylinder to TDC on the compression stroke, put lever forward to put car in high gear and block at least one wheel, both behind tire and in front. Air pressure applied to the engine can cause the car to move forward or backward if it is in gear, so block wheels securely. If the car is in neutral, applying air pressure can cause the engine to spin forward or backward unexpectedly. The cylinder under test must be at TDC on the compression stroke to do the test. Apply air pressure continuously during the test of each individual cylinder.

[Steve Jelf]

One way of finding TDC is with a wire or straw in the spark plug hole, but I think crank pulley pin position is more accurate.

https://dauntlessgeezer.com/DG97.html

[brendan.hoban]

I have since,

1. Pulled off the valve cover and checked that all valves are correctly gapped, lhey are at about 12 thou.
2. Taken out the plugs to check the intake valves, they all appear to be closing correctly,
3. Found No 1 TDC by cranking and grounding the plug,
4. Primed by pulling the choke wire and turned the crank to a position where it was about to spark on No.2
5. Turnmed on the ignition, it gave the usual chuff with about a quarter turn.
6. Cranked started on No 4 cylinder, it roared to life, no backfire!
7. Ran the engine for several minutes pre-adjusting the mixture, it was correct in the first instance.

So, it is still a mystery but the fault appears to lie with No.1 cylinder, I will try your air pressure suggestion to see if No. 1 intake is the culprit.

Incidentally, the timer rod goes a short distance to the right (it is a RHD) and I don't think is the culprit. The timer position is the same as it was for the Tiger and roller it replaced, about 20 degrees after TDC.

[Moxie26]

Thanks for the update

[dykker5502]

Incidentally, the timer rod goes a short distance to the right (it is a RHD) and I don't think is the culprit. The timer position is the same as it was for the Tiger and roller it replaced, about 20 degrees after TDC.

That does not say it is firing at the same spot. The internals are different. You are so close and it is so simple to check once you have it positioned at TDC to see if the coil buzz with the pin all up. I believe it just shouldn't.
But I agree that if you are certain it is only #1 it may not be a timing issue.

[nicklm]

You might run the car in the dark at night or in an enclosed garage. Look under the hood at the wires for all of the plugs. On our 26 the high voltage plug wires were close to the low voltage wires and the spark was going across from high to low in a place where they touched. I did not discover this until it was dark even though the spark was irregular and hard to find. I am sure you have checked for loose terminal attachments. Good luck.
Nick

[TXGOAT2]

It's a good idea to keep everything, including other plug wires and any other wiring, at least 1" away from the high tension plug wires. More distance is better. When the car is moving down the road at higher speeds, drafts under the hood may cause wiring to move enough to cause contact. Keep the plug wires well separated from each other and anything else, so far as is possible. Insulation on plug wires cannot be expected to always prevent voltage leaks, and it will do nothing to inhibit leakage via induction.

[TXGOAT2]

A low float level could contribute to lean backfire on startup.

[Norman Kling]

Interestingly, Thursday, I drove my 26 about 15 miles each way on a visit to a school. When I first started out, it spitted and sputtered and acted as if it would quit. I enriched the mixture and it ran better. After I had driven a mile or so, I leaned the mixture to the point I usually drive. Every so often it would spit or sputter all the way to my destination. After being there about 3 hours I started out for home and it did the same thing. I then adjusted the richness to where it began to surge and then opposite way to where it began to slow down and then set the mixture half way between and it ran very well as usual all the way home.
On a 26 the mixture adjustment is on the same rod as the choke. There is a raised tab on the knob so you can tell which position it runs best and set it to that position. Recently I had that rod off the car and the end at the carburetor swivel is square, so the rod can be installed in any one of 4 positions. I found it to be just one quarter turn different than before I took it off. So when I left for the trip, I had it adjusted wrong!
Anyway, your car probably has a different rod for the adjustment, but try turning it one direction till it begins to run rough then in the opposite direction till it starts to run rough and set it half way between, and if you are lucky, you might have solved your problem.
Norm

[TXGOAT2]

There's usually some slack in the linkage, and that has to be accounted for. Parts wear fairly quickly due to engine vibration.

[TXGOAT2]

It's a good idea to check the manifold clamp bolts/nuts from time to time. They need to be tightened evenly. An engine that has run for a good many miles may benefit from snugging them up a half turn or so. Also check carburetor to manifold fasteners.

[brendan.hoban]

Thank you all for your advice, I suspect I have a problem with No 1 inlet valve so the head has to come off.

The valve is a new one-piece stainless in a new seat insert and all valves have adjustable followers.

Does anyone have experience with reusing head gaskets, I have one left but it is a silicone gasket and I've heard bad things about these gaskets.

[Jerry VanOoteghem]

Thank you all for your advice, I suspect I have a problem with No 1 inlet valve so the head has to come off.

The valve is a new one-piece stainless in a new seat insert and all valves have adjustable followers.

Does anyone have experience with reusing head gaskets, I have one left but it is a silicone gasket and I've heard bad things about these gaskets.

Did you ever do the leak down test that others have suggested? Have you done a compression test? Either one of these would confirm a leaking valve without removing the head.

[TXGOAT2]

You do not need to remove the head to check the valves for poor seating, weak springs, improper adjustment, etc.

I don't think you can expect to re-use a modern type head gasket. Original type head gaskets have been re-used sucessfully, but a new gasket is always best.

[TXGOAT2]

Did the backfiring issue begin immediately when the new valve was installed?

[Moxie26]

Since you have adjustable lifters, why not re-adjust gap.... save cost of time and head gasket.

[TXGOAT2]

Here's something cheap and easy to try:
Remove the #1 spark plug wire from the plug and ground it.
Then start the car as you normally do and note whether it backfires or not.
If it does not, try the same procedure several times.
If still no backfire, replace the plug wire on #1 and try again.
If it again backfires consistently, the problem is clearly on #1.
It could be an ignition issue, an intake gasket leak, or a carburetor issue, or one of several valve issues.

A leaking or sticking intake valve might be expected to produce a backfire at the carburetor on starting, and perhaps on acceleration, especially before the engine is fully warmed up.

If the engine runs smooth at all times EXCEPT when starting, it suggests that the problem is not a valve issue, although it doesn't entirely rule it out.

I'd be very hesitant to pull the head on an engine that runs well once started.

[Altair]

Good vacuum is most important for a good running engine. Your issue does sound like a fuel mixture inconstancy. I would suggest removing the intake manifold and place a straight edge across it and see if there is any daylight showing through. It may need to be reground flat. I have some intake and exhaust manifolds from an unrelated engine, and they were all warped and required regrinding. If there is a vacuum leak no adjustments will fix it.

[brendan.hoban]

I am an idiot.

I obtained a new copper gasket so i decided to pull the head off to discover....................no problems.

All pistons and vcalves were operating correcxtly and threr was no leakage anywhere even around the head gasket.

So, thank you Robert Thompson for the correct answer, with the head off I connected No. 1 plug, turned on the ignition and slowly brought No. 1 piston to TDC......... to find that it was firing early!!

I used the head off opportuniry to grind the valves, decarbonise the head, replace bent valve pins and will reinstall everything when I have the time.

Then I will refit the Tiger timer, adjust the (RHD) timer linkage to ensure that it fires AFTER TDC.

Thank you all for your suggestions, I'll let you know if it is successful.

[TXGOAT2]

Be sure to set the valve lash correctly. It might be a good idea to install new valve springs, too.

[Moxie26]

Hey Brandon how you doing ? .....any progress report on your car?