The Ford Barn

The Ford Barn (
-   Model A (1928-31) (
-   -   Terriable backfiring (

Cape Codder 10-10-2018 09:39 PM

Terriable backfiring

My car has been running badly for quite some time. The latest problem is it is Backfiring! I have changed the condenser which did not help. I tried to take it out for a ride today and as usual, I took it out of the garage to let it warm up. While it was running it Backfired, at idle and then shut down. Any idea's?

Chuck Sea/Tac 10-10-2018 09:45 PM

Re: Terriable backfiring

Does it idle smoothly?
Is it hard to get it to idle?
I would look for a leaky intake gasket or cracked manifold
Try shorting each plug, one at a time and see if that changes the idle. That will narrow down a lean cylinder.
Do you have full flow gas feeding the carb?

Cape Codder 10-10-2018 10:28 PM

Re: Terriable backfiring

Chuck Sea/Tac Thanks for the response and ideas.
Idle seems to be smooth and not hard to get to idle.
I recently changed the intake/exhaust manifold gasket (can't say when).
I will check for the leaky intake gasket or cracked manifold.
The other two suggestions I will try tomorrow.

Magicbox51 10-10-2018 10:33 PM

Re: Terriable backfiring

Check your GAV. You might be running it too lean. Leaning it out will cause backfiring. Another issue I saw on another person's car was some dirt or something in the distributor causing cross-fire to wrong cylinders. In that case a new distributor body and cap solved the problem.

Ford Acar 10-10-2018 10:39 PM

Re: Terriable backfiring

Had you remembered to advance the spark after starting?

DJ S 10-10-2018 11:03 PM

Re: Terriable backfiring

Closing point gap?

eagle 10-10-2018 11:09 PM

Re: Terriable backfiring

Use a propane torch, unlit. Turn the gas on and direct the gas stream around the intake manifold as the engine is running. If there is a change you have a leak. Can also use WD40 but it makes a bit of a mess.
As previously posted. Check point gap. Usually point gap too close makes for hard starting as well.

Synchro909 10-10-2018 11:58 PM

Re: Terriable backfiring

Have you played with anything lately? If so and it was running OK beforehand, that is the place to start looking.

Jacksonlll 10-11-2018 06:05 AM

Re: Terriable backfiring

Try a condenser that you know is good, not a new one. A bad new one can really fool you.

Jacksonlll 10-11-2018 07:45 AM

Re: Terriable backfiring

Make sure the spring is not broken on the point arm. We had one where it would idle, but at speed, the broken spring would let the arm float. Just feel it to make sure there is guts to spring.

JRN1967 10-11-2018 09:00 AM

Re: Terriable backfiring

I had one that would start and idle but when I gave it gas it would backfire. It had been sitting for a little while. Critters crawled into the exhaust and plugged up the muffler.

I removed the muffler and shook all the acorns and nesting out. It stopped backfiring.

Cape Codder 10-11-2018 09:41 AM

Re: Terriable backfiring

How can I check a new condenser to see it is good?

Jacksonlll 10-11-2018 10:01 AM

Re: Terriable backfiring

Hook both us. They can't both be bad. It won't hurt anything. Just use some jumpers to ground the loose one and to connect it to the passenger side of the coil.

frank55a 10-11-2018 10:10 AM

Re: Terriable backfiring

It is also possible that you have a cracked distributor body or a brake-down in the insulation between the leads in the body. A number of years ago some repo bodies were defective and would crack near where the #4 internal lead went past the #3 plug lead causing the a short between the #3 and #4. This short is very visible if you run at an idle in a dark garage, check along the edges of the body near where the plug leads are close to the body. Try another distributor body. After I found out about this problem we had a tune-up clinic and I found about 1/3 of our clubs cars had bad distributor bodies.

Ernie Vitucci 10-11-2018 10:58 AM

Re: Terriable backfiring

Good Morning...A few more odd things to check would be the nuts on the back of your amp meter and the nuts on the back of your ignition switch if you have an after market switch instead of the original pop out. Another spot that can be a problem is the little fuse box on the side of the starter. The rivet can work lose and the connection can be lost and it will behave as if you are turning the ignition off and on. Just remove the little box and put things back like Henry had them for an hour or so and see if the problem goes away. Good Luck...Ernie in Arizona

Jacksonlll 10-11-2018 03:28 PM

Re: Terriable backfiring

That's right. If you have a make-break condition in the circuit from the coil to the point arm, it will backfire.

Synchro909 10-11-2018 04:23 PM

Re: Terriable backfiring


Originally Posted by Jacksonlll (Post 1684631)
That's right. If you have a make-break condition in the circuit from the coil to the point arm, it will backfire.

Some repro switches have loose terminals at the back. Give them a wiggle (I love these technical terms!) to check. If there is any movement, get back and I'll expain again how to fix it.

Cape Codder 10-13-2018 06:55 PM

Re: Terriable backfiring

FIRST I want to thank everyone that has responded to my "Terrible backfiring" post.

We have tried: changing the distributor body & cap, re-gapped the points, changed the condenser, changed the coil & coil wire, re-timed the engine, checked for vacuum leaks at the intake/exhaust manifolds, did I say retimed the engine cause I forgot to tighten the screw on the cam, used a jumper to check the ignition switch, adjusted the GAV from almost closed to 1/4, 1/2, and maybe as much as 3/4. After these few checks, we still have a Terrible Backfiring.

Soooo.......we are thinking of changing the plugs. We found the washers? on the bottom of plugs crushed and don't seem to be sealing. Don't know for sure about that but they sure are flat. However, the plug tips are a lite tan color with no oil or soot.

I have Champion W16Y plugs in there now but which one do most use looking at the below chart which was posted by someone on this site? Should I have a hotter or colder plug?

Champion (hotter down to colder):


Thanks for any help you can supply because we are at witts end with this problem.

DJ S 10-13-2018 07:16 PM

Re: Terriable backfiring

I think you need to investigate beyond your ignition system. If your sparkplug washers were "crushed" and causing a bad seal, you would hear air rushing out around the plugs when cranking over the motor.

Have you conducted tests to check on the health of your motor?

Curtis in MA 10-13-2018 07:26 PM

Re: Terriable backfiring

With mine it was rust in the tank. Put the filter in the tank and a strong magnet on the outside.
Never has backfired since.

heneste 10-13-2018 07:52 PM

Re: Terriable backfiring

Similar to what Curtis has mentioned, I've run into fuel blockages due to rust (either in tank or sediment bowl) and with movement of the vehicle it can stir up the sediment and block the fuel flow. Likewise, any sediment that makes it into the carb can also cause this intermittent backfiring but periodic cleanings of these parts may correct it if it's a fuel issue.

1crosscut 10-13-2018 07:59 PM

Re: Terriable backfiring

Check to make sure the spring on the moveable arm of the points is strong enough. It was mentioned in an earlier post. Hook a fingernail on it and pull it apart. It should give you a bit of a tussle.

A bad flexible wire under the upper plate can cause the backfire at high rpms too.

Did you recently have your carburetor apart? Leaving out the venturi will cause similar troubles.

Cape Codder 10-13-2018 09:41 PM

Re: Terriable backfiring

One test we did I failed to put forward was the fact we grounded each plug.
#4 showed a significant change in idle speed, #3 showed very little change, #2 showed a good change and #1 had NO change.

That was really the reason we have considered changing the plugs which have 6-7 thousand miles on them.

Marshall V. Daut 10-13-2018 10:13 PM

Re: Terriable backfiring

'Sounds as if you are about ready to consider the weird causes of misfires since you've just about exhausted the list of usual culprits. So, odd though it may sound, try this: Take off the terminal box cover and wiggle the bolts sticking out. If either is loose or can be pushed in and out, it's possible that the heads are touching or arcing against the metal firewall and creating a misfire. This will be especially likely when the firewall gets warm and the metal expands to close the gap between itself and the stud heads. In the 1970's, a couple inferior and somewhat shady parts vendors (old-timers know whom I mean!) imported lousy terminal boxes that had bolts with the heads too big to be completely sunk into the plastic body. The holes were not countersunk deep enough, either. In any event, after some use and vibration, the bolts loosened up and moved ever so slightly (but enough!) towards the firewall, causing occasional arcing and misfiring. This happened to me personally in Germany in 1974 in my 1928 roadster. I swapped out EVERYTHING while sitting along side the Autobahn as you have done, but couldn't fix the misfiring. 'Drove me nuts!!! Cutting to the chase, it turned out to be one of those poorly-made reproduction off-shore terminal boxes with the too large head bolts and shallow countersunk holes. I have since diagnosed a couple other instances locally that perplexed the owners because they couldn't find the source of their Model A's misfire. They also had older terminal boxes that had been bought "on the cheap" from the same suppliers. There are probably still hundreds of them out there waiting to ruin some Model A owner's day.
I'm guessing if you have a car that was rebuilt or "restored" in the 1970's or 1980's, one of these timebomb terminal boxes may be at fault. If the two studs are not loose, back off the four mounting screws inside on the firewall, pull the terminal box out a little ways from the firewall and keep it separated by inserting a couple pieces of cardboard. Then start the engine and drive the car. If there is no miss, you can bet that one or both stud slot-head bolts is/are arcing against the firewall. It may be a long shot, but you've tried just about everything else.
Did I miss that you performed a compression check to ensure that a valve isn't stuck or burned out?

katy 10-14-2018 09:05 AM

Re: Terriable backfiring

Pull the side timing gear cover and check the large timing gear.

1crosscut 10-14-2018 10:42 AM

Re: Terriable backfiring


Originally Posted by Cape Codder (Post 1685304)
One test we did I failed to put forward was the fact we grounded each plug.
#4 showed a significant change in idle speed, #3 showed very little change, #2 showed a good change and #1 had NO change.

That was really the reason we have considered changing the plugs which have 6-7 thousand miles on them.

Change the location of the plugs you have in the car and see if they have the same symptoms in different cylinders.

steve s 10-14-2018 12:51 PM

Re: Terriable backfiring

You've checked a few likely culprits but not ALL.

Battery terminals tight?

Auxiliary ground strap needed?

Ammeter and connections thereto? check by attaching jumper to junction box lugs.

Pigtail in distributor?

Swap with a good carb?

GPierce 10-14-2018 01:10 PM

Re: Terriable backfiring

Mine was caused by trash in the carb.

1931 flamingo 10-14-2018 05:49 PM

Re: Terriable backfiring

Go ahead and change the plugs, nothing to lose. Put in W-18's NOT 3X's, it will be cheaper to experiment this way.
Have you ck'd compression??
Paul in CT

Cape Codder 10-14-2018 08:19 PM

Re: Terriable backfiring

Soooo……many questions to answer so here goes:
Frank 55a As I have said I have changed out the Distributor body AND Cap along with the Coil wire. Ernie I had checked the nuts on the amp meter and ignition because I was in there to check amps on the back of the meter. Nothing lose at that time so I’m holding off taking the dash down again. As to the fuse box I don’t have one on my car. Synchro909 I’m thinking you meant the ignition switch, see above. Curtis in MA I had drained the gas tank at Gettysburg last year to check the filter and found nothing but a clean filter and not bragging but a very nice clean tank. I think I will hold off on checking this again for awhile. Heneste see previous answer. 1crosscut I have been in there to check the arm of points several times in adjusting points cause I want it perfect at .020” and never felt the spring to be bad. As to the flexible wire under the upper plate I plan on checking this again. No, I haven’t taken the carb. apart and I wouldn’t leave out any parts anyhow HA! HA!
Marshall V. Daut I have to say I had that box apart because the back part of the box was cracked OR I took it off for the same reason you mentioned about the bolts. I remember using RTV on the back of the bolts so I’m hoping it would be good for five years. But this is another suggestion I have to keep in mind if I don’t find anything else. NO, you didn’t I had done a compression check . We actually had a suggestion from a non-fordbarner and non-Model A’er to see if we have a leaking head gasket BECAUSE when I went to short the plugs two of them didn’t really have any change in RPM. Katy now you are talking about something I don’t want to get into especially when I’m trying to find something simple, HOWEVER I will keep it in mind. 1crosscut I’m sorry but I don’t understand your suggestion or I guess what I don’t understand is what would it prove? steve s I actually disconnect my battery for the non-season and when getting it ready to get back on the road I always wire brush the posts, and cables, put electro (sp?) grease on each post then check the battery with a hydrometer done maybe 600-700 miles ago. The pigtail was screwed all the way in so I backed it out about two threads. I just had screwed it in with my fingers, no pliers. 1931 flamingo W18 Y’s are planned. No compression check but see above.

Thanks again to all who have responded and given me advice which I really appreciate. I’m just trying to get the info in some sort of order. By the way sorry for the rambling but trying to talk to everyone.

steve s 10-14-2018 08:48 PM

Re: Terriable backfiring

a great case study in randomly trying things versus systematic trouble shooting, still playing out.

1crosscut 10-14-2018 09:16 PM

Re: Terriable backfiring

What I meant by changing the positions of the plugs was to take
#1 plug to #2 cylinder
#2 plug to #3 cylinder
#3 plug to #4 cylinder
#4 plug to #1 cylinder

Then see if shorting out the plugs has the same result as your first test.

Cape Codder 10-14-2018 09:29 PM

Re: Terriable backfiring

I understand what you are saying BUT what does it prove? Please explain.

PalAl 10-14-2018 09:37 PM

Re: Terriable backfiring

Check all your electrical connections then do a load test on the battery. Sounds stupid but a friend had the same problem and it turned out to be a bad battery. Who would have thunk it!

1931flathead 10-14-2018 09:47 PM

Re: Terriable backfiring

If you switch plug if they miss in the same ones they miss in now you know your plugs are good

Cape Codder 10-14-2018 10:35 PM

Re: Terriable backfiring

First - 1931flatheadthanks for the response and explanation. I will try that.
PalAl - also thanks for your response and suggestion.

Boy, do I have a lot of work ahead of me in the next couple of days with all the suggestions.

Thanks again!!

holdover 10-14-2018 10:41 PM

Re: Terriable backfiring

When I get into something like this it sure can be frustrating, I like to eliminate many items at one time, just a thought have you considered "Hot Wiring" to eliminate the key switch, and all other electrical circuits other than the points, condenser and coil. A simple jumper from the starter terminal ...

Cape Codder 10-14-2018 10:47 PM

Re: Terriable backfiring

holdover Thought I said "used a jumper to check the ignition switch" in post 18 which eliminated the switch, OR so I think. Thanks for your response!

Rich in Tucson 10-14-2018 10:59 PM

Re: Terriable backfiring

Just fixed one like yours. Idled great, would run several quarters of a mile then sputter and backfire. Then start right up and repeat as you waited to get back into traffic.

Gas flow to carb was a dribble from disconnected fuel line. Blew air into tank from gas line and found high resistance (~15 psi to overcome). Checked screen in gas sediment bulb = clean. Disconnected interior gas line (was a repro fat one) and found it packed full of rust like coffee grounds.

About 12 weeks ago the leaky fuel shut off valve was replaced with an Ace Hardware ball valve complete with yellow natural gas teflon tape sealant and the stand-up in-tank filter was removed opening the floodgates for years worth of crud to descend into the fuel system and reduce flow to a trickle good enough for idle but not for go.

I have replaced a lot of corroded/dissolved/and as a result plugged in-tank filters and cursed them all the while but they do serve a useful purpose if they are installed AS A CONSUMABLE MAINTENANCE ITEM (around here 3-5 years is pushing it for trouble) and not a permanent fix.

1crosscut 10-15-2018 06:46 PM

Re: Terriable backfiring


Originally Posted by 1931flathead (Post 1685568)
If you switch plug if they miss in the same ones they miss in now you know your plugs are good

Thanks, that is what I was getting at.

All times are GMT -5. The time now is 06:35 PM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2019, vBulletin Solutions Inc.