Backfiring

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Model T Ford Forum: Forum 2012: Backfiring
Top of pagePrevious messageNext messageBottom of page Link to this message  By Sam Humphries on Saturday, May 26, 2012 - 05:01 pm:

I am new to driving a Model T. Have driven it around the neighborhood but not for longer outings. Took it out this morning for a run across town to our local Woodcraft Memorial Day event and all went well for about 4 miles through town. Suddenly it had a very loud backfire and smaller ones as we progressed. I switched from magneto to battery and it ran very well without backfiring. As I said I am new to driving T's. I tried making advance and throttle adjustments to prevent the backfiring to no avail. Adjusting the spray needle while in motion also did not help.

Any thoughts on what is happening. Timing is set to 2 1/2 inch when fully retarded. New float valve and spray needle and spray nozzle. Float is set to just under 1/4" from flange to float.

Temperature ran 160 in motion and would rise slightly when stopped for lights.

Thanks Sam


Top of pagePrevious messageNext messageBottom of page Link to this message  By Cameron Whitaker on Saturday, May 26, 2012 - 05:10 pm:

It could be that your coils aren't adjusted properly. T coils typically run much better on magneto than battery, even if they aren't adjusted perfectly. If they are adjusted well, then switching over from battery to magneto is almost like NOS for a T!

Now is your car genuinely backfiring, as in out of the carburetor, or is it after-firing in the muffler?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Sam Humphries on Saturday, May 26, 2012 - 06:23 pm:

Backfiring in the exhaust would best describe what happened. The coils have been rebuilt by the Coilman just weeks ago. The switch from battery to magneto seems OK after starting. I have adjusted the spray needle closing until it begins to run rough and open until it runs rough and split the difference. Seems to run best a just under 1 full turn.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kenny Edmondson, Indianapolis on Saturday, May 26, 2012 - 06:33 pm:

With out knowing your engine, I would say you have a weak mag and need to check your mag output. The easy way to get and idea without any test equipment is to take a 12 volt light bulb and ground the brass portion and touch the contact to the mag post. At idle it should be dimly lit. At a higher RPM it should get really bright and burn out. You might want to remove the mag post first and check for lint build up.


Top of pagePrevious messageNext messageBottom of page Link to this message  By George_Cherry Hill NJ on Saturday, May 26, 2012 - 07:08 pm:

Prob mag output issue, but...

Do pull the timer and take a look inside first. Had one last year that drove me nuts on a freshened roll-out. Had same issue, backfiring, popping. Maybe 8 miles on it and it was horrible, switched to 'batt' and ran lots better with no backfires and pops but didn't have must get up and go but good enough to get home.

My timer had less than 200 miles on it so never thought to check it but did tear down and rebuild replace everything else in ignition and carb with still the same problem. Finally with only timer left, popped it open...it was already 'shot' with lots of ripples and a turned/tilted pole piece inside. Swapped timers, no more problems!

All I can surmise is the slight differences in actual firing between mag and batt source were more generous at ignoring the roller bounce when set to batt.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Saturday, May 26, 2012 - 07:34 pm:

Definitely look hard at the inside of the timer. If the timer gets dirty inside they often will run fine on battery but not on MAG. Be sure there is plenty of timer lubrication. I recommend you pack it with wheel bearing grease, any kind that does not contain graphite or molybdenum. In other words tan color or red color.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Cameron Whitaker on Saturday, May 26, 2012 - 07:45 pm:

Oops! I thought that you said that you switched from battery to mag. I had it backwards!

I would definitely say check the timer. Make sure that it's not worn or filthy. Also, if you have a voltmeter, you can check the magneto's output. Set it to AC and check the voltage coming out of the magneto post on top of the hogshead to ground. Make sure that your meter lead is making a good connection to the chassis! 7 volts is about the minimum acceptable voltage for the magneto at a low idle. Any lower than that and you are almost certainly are having magneto problems.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Saturday, May 26, 2012 - 09:35 pm:

A few things. Were you going downhill when it happened? The Model T will tend to pop in the exhaust system when going downhill with the throttle closed. This would happen whether on battery or on magneto.

Another thing, when it happened, did you try to change the position of the spark lever? It could be that it is just about to go to the next segment of the timer when it fires. This is hard to explain, but when you are running on mag, you will notice that when you pull the spark rod down, it doesn't affect the way the engine runs until you pass a certain point on the quadrant, and then the engine speeds up. If you happened to be running right at that point where it jumps from one segment to the next, you could get a little rough running. This is so only if you are on magneto. If you are on battery, the transition is smooth all the way as you move the spark lever. So if it happens again, try either advancing or retarding just a notch or two and see if it stops. Other suggestions could also be the cause. Those are mentioned above. Coils out of adjustment, weak magneto, dirty timer. Anyway start with the easiest to do, such as adjusting the position of the spark rod, cleaning the timer. Then work from there. You will eventually find the cause.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dale Peterson on Sunday, May 27, 2012 - 01:13 am:

My 15 started doing the same as you describe, tried everything as suggested to no avail, at times does not run on mag at others it is rough and "backfires". Recently remembered a few years ago that the wire in the coil box from mag post to switch was broken and I replaced it. Now my next step is to check this wire, I am suspecting a cold solder joint or the wire came loose. Check this souse also. It's the pits to keep fixing the muffler when the unburned fuel explodes and the muffler outer tube bounces off the ground!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Sunday, May 27, 2012 - 10:15 am:

A couple of other things not mentioned above. Lint on the magneto terminal. you will need to remove the magneto plug contact at the top of the hogs head, and check for lint. If it has lint, remove it. Another thing is the magneto plug contact itself. On some aftermarket plugs, especially the ones with an oiler tube connected, the contact is not long enough to make a good connection with the solder spot at the top of the magneto. Check this too.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron Patterson-Nicholasville, Kentucky on Sunday, May 27, 2012 - 10:51 am:

Sam
Sometimes coils conk out.
If you like drop by and we can check them out in just a few minutes just to be sure.
Ron the Coilman


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