BACKFIRING THRU CARB

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Model T Ford Forum: Forum 2017: BACKFIRING THRU CARB
Top of pagePrevious messageNext messageBottom of page Link to this message  By Danny_s on Monday, May 08, 2017 - 10:57 am:

My '23 touring ran fine yesterday for about
40 miles of total driving, then i noticed a
stumble/skip just one or two times. i shut the
car off, had lunch, and got back in. it started
fine, i pulled out in the road and shifted to
high, then it started popping thru the carb
every three for four seconds, running smoothly
in between. Any Ideas?? I checked for loose wires
and found none.--- The car has NO POWER to move at all.
we had to trailer the old girl home...


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Strange - Hillsboro, MO on Monday, May 08, 2017 - 11:18 am:

Sorry to hear that. :-( My initial thought based on your description:

Check for a broken intake valve spring or broken retainer or retainer pin.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Tomaso - Longbranch,WA on Monday, May 08, 2017 - 11:20 am:

The carburetor mixture rod might have "vibrated" itself to a leaner (closed) position - clamp nut needs to hold the adjuster snug to prevent that again. Close the mixture rod clockwise until you feel slight resistance then open it back C.C.W. around 1 & 1/2 turns to start then after it warms up to operating temperature, begin to lean out to best throttle response.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Tomaso - Longbranch,WA on Monday, May 08, 2017 - 11:22 am:

I also agree with Mark and I had an adjustable lifter break once indicating a similar condition.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Monday, May 08, 2017 - 11:41 am:

I would suspect what Steve said. Try what he said first. If what Steve said doesn't work open the drain cock at the bottom of the carburetor, the fuel should drain out in a steady stream. If it just drips, you have a clog in the fuel system which needs to be addressed.

Another problem which I encountered once happened right after I filled the gas tank. Several other T's got gas at the same station and had the same problem. The fuel was bad. So if your problem happened right after you got gas, that could be your problem.

If you have a compression gauge, check the compression on all cylinders. Should all be near the same and around 50 PSI. The actual amount can vary by altitude and by the type head you have on the engine, but stock is between 45 and 50 at sea level. If one or more cylinders have low compression, you likely have a bad valve.

If compression is even and your carburetor adjustment seems to be OK, next step is your ignition. Check to see if all spark plugs are firing. If you can get the engine started, run at a fast idle and ground one by one the spark plug leads. If it makes no difference when you ground one of the plugs that one is not firing. If the engine slows and runs rough when you short one, that one is functioning.

You don't state what kind ignition system you have. If you are running the timer and coils you can start by cleaning and inspecting the timer. If it is original, use some non conducting grease on the roller. If a New day, leave it dry or if an Anderson, clean and use the special grease made for it.

If you have the coils, try switching coils from one position to another. If the misfire follows the coil, you have a problem with that coil. If it stays in the same location, the problem is in any of the following: Burnt carbon trace on wood in coil box, grounded or open wiring between coil box and timer, or the spark plug and the wire connecting the spark plug to the coil box.

If you have a distributor, check the rotor and cap for a carbon trace or burnt area. Also burnt or improperly gapped points could be the problem as well as a defective condensor. If you are using a tru-fire, or e-timer you will have to ask someone else, because I have no experience with it or with the e-timer.

It is always a good idea to carry a few good spark plugs along with you and one or two good coils, just in case, and on long tours maybe even a spare timer.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jem Bowkett, Spalding United Kingdom on Monday, May 08, 2017 - 05:36 pm:

Check the carb is tight on the manifold and the manifold is tight to the block


Top of pagePrevious messageNext messageBottom of page Link to this message  By Charlie B actually in Toms River N.J. on Monday, May 08, 2017 - 05:57 pm:

While I am a big fan of taking a comp test, (both dry & wet), I'm not sure it'll show a failed or weak intake valve spring. Especially if your popping back is occasional as opposed to constant. By all means check your fuel flow and Carb needle setting. Next attempt to isolate the cylinder causing the problem by shorting out the plugs. I suggest fuel because of your symptom description. 1 bad cyl. would cause low power and a noticeable miss but not no power. As stated above the most common answer is fuel delivery next is an intake valve problem. Could involve an intake manifold/gaskets lean running problem but if one is blown it'll affect 2 cylinders as the 2 intake ports feed 2 cylinders each.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bill Robinson, Salty Bottom, AL on Monday, May 08, 2017 - 07:02 pm:

Danny- I had a car that was backfiring through the carburetor.
The problem turned out to be the timer with a carbon brush that had so much accumulated carbon dust in it that the dust was shorting multiple plugs at the same time, causing backfires through the carb.
Take a look at the timer before getting too deep in your troubleshooting. Look for the simple stuff first.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim Wrenn-Monroeville OH on Monday, May 08, 2017 - 07:57 pm:

Us folks with carbon brush timers gotta remember to open 'em up at least once a year and clean 'em out. Of course if you drive more often, clean 'em more often! This also gives you the opportunity to make sure your cam seal isn't leaking any oil, as the carbon brush timer hates oil!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Danny_s on Tuesday, May 09, 2017 - 03:16 pm:

Here is what i found.... I first started the engine, and found it to be the #1 cylinder by
grounding out with a screwdriver. I first swapped
#1+#2 coil boxes, and still got the same result.
Then I swapped plugs, and still got it to back fire.
It only backfires when not shorted with the screwdriver. With the screwdriver,
the backfiring ceased completely,and the engine ran much smoother, albeit with a skip.

I am inclined to agree it might be a valve spring
or retainer pin. That is what we will look at next.

As always, thanks to you all for the info and help.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Danny_s on Tuesday, May 09, 2017 - 03:23 pm:

My timer is a roller set up. I will open that up
just to rule anything out there also.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Tuesday, May 09, 2017 - 08:56 pm:

It might be possible that #1 wire between the coil box and timer might be grounded. That would produce a constant spark which would cause the gas to burn on the intake stroke. When you short the plug, the spark will stop.
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Tuesday, May 09, 2017 - 08:59 pm:

It is possible that the wire between the coil box number 1 and the timer is grounded. That would cause a constant spark and the gas would be burned on the intake stroke causing it to pop in the carburetor. When you ground the plug it stops sparking. So check that wire.
Norm


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