Backfire

[DonaldSmith]

My ears are still ringing.  Maybe fifteen minutes to a half-hour ago, I was working on my ignition when I heard the loudest bang.  

 

I tried to adjust the points on my distributor, and did something wrong.  At one point I used white-out to mark the minor adjustment, so that I could get the distributor back where it was, but in my fumbling, I got some on the points.  A test light showed that I was not getting the interruption of the ground circuit for the coil.  Then I bench-tested the distributor and couldn't get any grounding.  I filed the points and set them, and was getting good action with the test light.

 

I reinstalled the distributor, and tried to start the engine with my remote starter.  Button for neg cable to solenoid,  ignition switch to power the negative post of the coil.    It's worked before.  I cranked the engine and could see the the plugs were firing, with a neon tester that goes in series with a plug wire.  Maybe a few cranks, no  firing, and BAM! 

 

I undid the remote starter and tried to start the car from inside.  More bangs. maybe not so loud. 

 

Theories:  Could I have loaded the exhaust piping with fuel-air mixture, just waiting to blow?  When I was a kid, I would shut off the ignition when the car was moving, and turn it on again, to get a pop.  Once, I did it once too often, and blew the muffler,  The driveway was next to my folks' bedroom, so I couldn't sneak up the drive.  Maybe this is payback time.  I haven't checked the exhaust system today.

 

I did advance the timing a bit before this episode.  Could that do it? 

 

Should I try to start the car again?  Any more suggestions?  

[Dodgeb4ya]

You might have a bad muffler.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Now.

[Plymouthy Adams]

yes...you can have upset the air fuel mixture..you could also have accidentally moved the engine and reinstalled the distributor 180 out..if I had a dollar for every time I have come across this I could drive a Ferrari..(did not say own mind you, just drive one)

[_shel_ny]

Follow the static timing procedure

[DonaldSmith]

It keeps going pop when I try to start it.  I'll do the static timing.

[Don Coatney]

Here is some static timing information I posted a while back.

 

Don Coatney

Don Coatney

1948 P-15

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Posted 28 June 2014 - 04:40 PM

This thread has been unsolved for a long time. So I will tell my story from earlier today. My car had been running really good until I went for a drive yesterday. My engine developed a slight irregular misfire with no repeatable pattern. I suspected an issue with adjustment of my dual point setup so the first thing I did was pull my distributor. I set up my bench test using an electric drill, power supply, and test coil. I found a slight variation in dwell angle. I made a very slight adjustment in point gap and corrected that issue. Upon reassembly I discovered what I believe was the real problem. A cold solder joint on the power supply wire from the coil to the distributor as pictured below. I made this cold solder joint recently but I used my small solder gun and not my big iron. So I made up a new wire and corrected that problem.

 

Prior to pulling the distributor I brought the engine to TDC and noted the rotor position. Having made the slight point adjustment and correcting the cold solder joint I re-installed the distributor and positioned it very close to the same position it was in when I removed it. I made an attempt to fire the engine and it was a no go. I made attempts to fire the engine with my remote starter button and a hot wire under the hood while turning the distributor under the hood and it was all a no go. I connected my timing light while cranking the engine with the starter and found my timing was a good way off from TDC. So I brought the engine to TDC using the starter motor. I pulled the plug wire from #1 spark plug and connected it to a spare plug sitting on the head. I then (without spinning the engine) moved the powered up distributor until I was getting spark exactly at TDC correctly static timing the engine.

 

As I had been spinning the engine a lot with no fire I suspected my plugs may be fowled so I removed them and sand blasted them. While the plugs were out I also used an air gun down the plug holes to clear the cylinders of any flooding. Reinstalled the plugs, hit the starter button, and the engine fired right up. I then used my timing light to dial it in.

 

So my point being correct engine timing is a very small window. If you take the time to insure your engine is correctly static timed and all other system problems are corrected the chance of starting is greatly improved.

[DonaldSmith]

Totally mystified! 

 

I set the crank to TDC, with the rotor pointing at 7 o'clock. (The shiny brass end of the rotor, not the fat end.) 

I connected a test light from the battery to the wire from the distributor (disconnected from the coil), and rotated the distributor counterclockwise until the light went out, and tightened the distributor bolt.  Nothing.  

 

Did I rotate the distributor clockwise instead of counterclockwise?  I installed a compression gauge to the No. 1 cylinder, with the release button clamped in, so that the reading would not build up and hold.  I installed a neon plug tester to the No. 1 plug, which was resting on the head.  Crank, crank.   Spark, then puff!  Dizzy way off!

 

Back to TDC, 7:00.  Dizzy clockwise until the light comes on, then counterclockwise until the light goes off.  Try it again.  Puff, spark.  Puff, spark.   But crank, crank, bam! 

 

Is my timing close, but far enough off to backfire?  Maybe my TDC measurement is off.  Which way can I nudge the dizzy?    

[Frank Elder]

It is possible your timing chain has jumped a tooth.........

[DonaldSmith]

Engine overhauled in 2004, some 3,000 miles ago.  New timing chain and sprockets back then.  Was the chain properly oiled all this time?  I think I got the little tube back where it's supposed to be.  Is there a way to tell if the chain has slipped, without removing the front cover?  Can I observe the valves closely enough to tell? 

 

The key question:  "What did you do just before this trouble started?"  Well, the engine had been running, with an occasional stutter, and symptoms of a stuck valve.   I removed the distributor, after carefully noting the position of the minor adjustment; I removed that bolt.  Then I set the points and reinstalled the distributor, at the same setting of the minor adjustment. .  

[Tom Skinner]

Donald,

Were you in the right T.D.C. and 7:00 Rotor pointing? That is to say, were you really at T.D.C.?

A four stroke engine appears to be correct twice with No.#1 at T.D.C. and Rotor at @ 7:00 (Check to see if the Damper Mark is at Zero - or 2 Deg B.T.D.C. when approaching TDC) 

Have you moved or replace any wires? Perhaps misplaced one in the Ditributor Cap?

Try again, you may find you were off. The Static Timing thing usually gets your engine started. Usually a retarded Timing Setting causes Backfiring out the Carb,

a too advanced timing setting backfires out of the tail pipe.

Good Luck!

Tom

[_shel_ny]

Back a while I had my oil pump out.

 

Did not move the dizzy.

 

Installed the pump per manual instructions.

 

The dizzy tang apparently did not drop in the pump slot.

 

When the engine turned the tang fell in 180 out.

 

I tried turning my dizzy, just as you have, but no start.

 

The forum replies got me to put things back where they belonged. (rotor)

 

I used a piece of tape to confirm #1 on compression stroke. (my compression tester is the type you have to hold in place. Not enough hands for that)

 

I used an inline spark tester to confirm that the spark was going to the #1 cylinder at the correct time.

Edited August 24, 2015 by shel_ny

[DonaldSmith]

I had TDC at the damper with the brass end of the rotor pointing at 7:00.  I have not moved any of the plug wires from the distributor cap, nor misconnected them to the plugs.  I double-checked the wires.  I checked the spark against a compression gauge, so I know I'm not 180 degrees off. 

 

But I may be be far enough off to cause this misery.  I had to extend the TDC pointer because I had added a pulley for the power steering.  The pointer could be a few degrees off

 

Tom, you say that if the backfire comes out the carb, the timing is too retarded; out the exhaust, too advanced.  That's the information that I was looking for.  

 

The backfire was so loud under the hood that I suspect it was out the carb.  (My ears were ringing for a half-hour)  Let's see:  too advanced, rotate clockwise to retard.    

[DonaldSmith]

I rotated the distributor clockwise, in successive tweaks, at the major adjustment bolt.  I went from one extreme of travel to the next.  The pops came out the carb, but with less cranking each time.  Each time, I quit cranking after the first pop.  Something has to be way off.  

 

I am contemplating the wonders of removing the chain case cover to inspect the chain and sprockets.  If there is no problem there, maybe I'll crank on the crank to get absolute TDC, per depth gauge at No. 6 cylinder, and verify the accuracy of the pointer at the damper.

 

Any other suggestions? 

[ptwothree]

When I am checking for #1 cyl. on the compression stroke, I pull that plug and turn the crank by hand using a big wrench while putting my thumb on the plug hole.  When I start to feel pressure on my thumb, I stop, and start watching the timing marks.  When I get to 0 degrees, stop.  Now I know for sure I have #1 cyl in firing position. Then I move the dizzy clockwise till my ohm meter makes noise.  If all else is well with the ignition and fuel system, wonderfulness will happen.

 

I used this method to start a freshly built 218 I had never heard run.  Cranked right up and runs great.

[casper50]

Have you checked that the no. 1 sparkplug wire is at the 7 o'clock position?

[DonaldSmith]

Compression on No. 1 thumb hole - Yep.

Rotor pointing at 7 o'clock - Ayup.

No. 1 spark plug wire at 7 o'clock - Right.

 

Here's the mystery:

Engine started and ran.  

I marked the minor adjustment, removed the bolt there, and removed the distributor.  I dressed and gapped the points.  I reinstalled the distributor in the same location.  I verified that the shaft and rotor were not 180 degrees off.

I checked TDC and tweaked the distributor rotation with the test light until the light went out.

I verified that I got compression on No. 1 before the spark.

Nothing but backfire (out the carb). 

 

I tried retarding the distributor progressively to the extremes of travel, and nothing but backfire.  The specter of the timing chain jumping a tooth presents itself.    

 

Can I verify whether the timing chain jumped, without removing the front cover?  Otherwise, it's off with the front cover,an elaborate procedure, and possible dead end.   

[Don Coatney]

I personally have never observed a jumped timing chain on one of these engines. Have you inspected your distributor cap with a magnifying glass for cracks? Double checked your plug wires to insure the right wire is going to the right sparkplug? And inspect the plug wires to insure the spark is not jumping from wire to wire in the loom?

[casper50]

check inside the dizzy.  wire, condenser.

[DonaldSmith]

Yes, mother, I checked TDC and 7 o'clock!  OK, just one more time, (grumble, mumble).

 

Compression gauge in No. 1 spark plug hole, crank it around, puff.  One o'clock!?  That must have just happened.  Someone sneaked in the garage and is messing with me.  

 

OK, reset TDC and rotor at 7 o'clock.  Set the major adjustment and minor adjustment near the middle of their ranges.  Put the test light on, rotate the distributor counterclockwise till the light goes out.  

 

Hey, with the major adjustment loose, it's possible to set the dizzy for the wrong plug.  I had the dizzy too far clockwise to start, set the wrong plug to fire.  No wonder things went Boom.

 

Being sure that the rotor was at 7:00, not 8:30, I did the trick with the light just going off, at the major adjustment and again at the minor adjustment.  Plugs back in, wires back on, the engine started and ran.

 

But now I think I blew out the muffler.  But what a sweet sound.  A muffler is no big deal.

 

Thanks, guys, for harping on me. 

 

(edit; add:) BOOM!

 

Edited August 24, 2015 by DonaldSmith

[Don Coatney]

As I have said the static timing "window" is very small.

[DJ194950]

Time for a glass packed muffler?

 

A back fire will also clean them out with only the loss of the glass packing.

 

muffler-clean out.htm

[ptwothree]

"rotate the distributor counterclockwise till the light goes out."   Should be, rotate the dizzy clockwise till the light comes on.  It is at that point that the plug should fire.  When the light goes off, the coil starts building a charge for the next time the points close.  Hope this helps.........

[Niel Hoback]

Spark occurs when the points open, collapsing the field in the coil.

[ptwothree]

Boy, am I dumb!!          Never mind.

[DonaldSmith]

Timing is OK, but the carb has to go.  

 

It takes starting fluid to start the engine, then it will idle forever.  Step on the gas, and the engine dies.  I know, vacuum advance.  I checked it with a vacuum pump. 

The car would stall when starting off, unless I used the clutch.  (Fluid drive.) Then it would run OK down the street.  

 

I considered rebuilding the carburetor, but figured it may not address the real problems. Bad dashpot?  Leaking around the throttle shaft? Other hidden things in the innards of the carb?

New carburetor arriving Tuesday from Carburetor Exchange.  They set up their rebuilt carburetors on an engine before sending them off.  We shall see.  Stay tuned.

 

I'm ready to sell the car, maybe in the spring.  I'm getting too old for this (insert scatological reference).