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Backfiring and afterfiring on a 26


Mpgp1999
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Hello

on my 26 12v under heavy throttle the car backfires and afterfires. In the past I had an issue with a valve stuck open in the vacuum tank and raw fuel entering the motor bypassing the carburetor. But the car idles normally, so I do not believe this is the case. 
 

thanks

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Update 

I cleaned and gaped the points and plugs. That seemed to help. Now it is much harder for it to backfire. But when it does pulling the choke a little stops it. The problem was probably dirty contacts, slight timing problem, improper mixture. I noticed the cam in the distributor has rotational play. About 15 degrees. Is that normal?  
 

new issue 

not charging. With key on the amp gauge shows about 8 amps discharge. At the battery there is no charge it is at 12v. At the generator it shows 13.5v under throttle. Any ideas. I’m pointing my finger at the starter switch. The two negative leads, from generator and battery, show voltage and 0 ohms. When I engage the starter it shows no voltage. Shouldn’t it be the other way around?

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The backfiring is being caused by a too lean mixture.

As I recall your car has the NorthEast starter/generator so I expect the foot starter switch is the same as was on my '24.

Removing that switch is no piece of cake but, in addition to the starter terminals inside, there is an electrical cutout for the charging system.

The points inside might need tuning up and, while it's handy, you might want to tune up the starter terminals as well.

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Pulling the choke out a bit to richen it may indicate a vacuum leak causing it to run too lean.  Have you ever had the carb apart to verify the dashpot is able to move up and down?  My distributor rotor has a similar amount of backlash that I suspect is normal.  

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On 3/2/2020 at 10:59 PM, cahartley said:

The backfiring is being caused by a too lean mixture.

As I recall your car has the NorthEast starter/generator so I expect the foot starter switch is the same as was on my '24.

Removing that switch is no piece of cake but, in addition to the starter terminals inside, there is an electrical cutout for the charging system.

The points inside might need tuning up and, while it's handy, you might want to tune up the starter terminals as well.

How do I service/check the cut out 

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You'll need to remove the starter foot switch box from the floorboard.  This involves disconnecting the wires on the back side of it and removing the two bolts that hold it to the floorboard.  Once removed, you can takes the screws out that hold the switch together, open the switch box to reveal the cut out relay.  Do you have the Mechanics Book of Information for the car?

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I have the starter button out. There is a coil and several contacts. Between the battery and indicator there is 67 ohms. The points are chalky white. I have an original owners manual. For some reason I have voltage between the battery and starter terminal. When I disconnect them the terminals show no connection. The same for the leads. But when connected to the switch there is continuity. 

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When I first purchased my 19 it would idle, but sputtered and backfired if I revved the engine. Then one day "bang!!!" Blew the seam in the muffler...very loud in a garage.

So I was checking everything, pulled the distributor cap and just happened to notice that the cap had the cylinder numbers on top by each plug wire. Decided it couldn't be that simple. Sure enough, the PO had crossed two of the spark plug wires. Simple switch and all was good...until the next issue....

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Matthew, I'm not sure if those battery maintainers put out enough juice but give it a shot.

If that happens to not work use the car battery. 

The solenoid will use only the amount of current for which it is wound.

You will figure out where both ends of the solenoid (electromagnet) are. 

Simply energize the coil (ignore polarity) and watch that the points close when energized.

That you mention the spring on the solenoid looks like new bugs me and makes me think it's probably too strong.

Over 93 years there may be a little wear here and there that may have to be compensated for.

My preference is to have the points close with less juice rather than more.

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If you suspect the coil isn't working or not working properly, there is the option of dispensing with the coil/relay all together by using a diode instead.  There are some threads on the forum that talk about  it.  I did it on my '25 and it was pretty easy and not very expensive.

DSCN3844.JPG

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I have two starter switches. One with a diode and another original. I get voltage at the starter generator while the motor is running. The amo gauge stays at 4 Amps discharge steady. There is no increase if voltage at the battery when there is throttle. I tried stepping on the stater while the motor was running and there was no change on the amp meter nor battery voltage. Currently the original coil starter switch is installed. 
 

the diode (on the bench) tests nothing one way and about 2 Ohms the other. 

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My Starter/Generator had bad field windings and behaved similar to yours.  When the SG is working properly, it should show maximum charge at idle and decrease as rpm goes up.   Here is a wiring diagram that shows how it should be hooked up.  I would assume for a '26, it would be the 8100-A switch.

Starter Switch.jpg

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UPDATE 

I Finally road tested and it failed horribly. Under a load the car will not operate. First gear I did not notice anything. One I got in the road it would not go faster than 10 mph. I had to nurse it to get there. The coil was very hot. The car idled fine. I changed the coil and there was no difference. The car kept backfiring. I changed the condenser to a spare I had. No spark. I put the old one back. Spark for 10 seconds. To add insult to injury it began to pour. Currently The car will not charge. The car will not stop and the car will not start. The motor will turn over. I have exhausted every resource and all my knowledge I have come to a dead end. Hopefully you guys can guide me. 

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I would go back to basics and double check things like the static timing, points adjustment and wiring connections.  Even if the generator won't charge, the car should be able to run on a fully charged  battery for quite a while (without headlights on).  If everything seems to be in order, I would then start taking a closer look at the carb.  Also, what do the plugs look like?

Edited by MikeC5 (see edit history)
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The plugs are new champion w18 recommended by the latest DBC newsletter. The points look pitted. The condenser failed the light bulb test. I ordered a “new” condenser from romar. My carburetor was rebuilt by Vern barker I am confident that it is at least close to proper adjustment. 

Edited by Mpgp1999 (see edit history)
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The spark plug wires are arching to the block. If they appear to be fine and running normally and I put my hand near them I will get shocked. They are recent wiring. New wires with cloth cover to look old. In the photo above you can see a part of a rubber hose. The spark goes through the hose to ground. I can see this happening. 

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One possibility is a defective part causing the firing voltage to be really high. Check your plug wires with an ohmmeter. Should be very low resistance if they are recent repro 7mm cloth wires (they don't make them in resistor versions). Look at your rotor and see if any pieces have fallen off. Look under your boots where the wires meet the cap for severe corrosion. Lastly, and maybe most importantly, look at the carbon button inside the distributor cap, and make sure it is contacting the rotor.

Edited by Bloo (see edit history)
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Well, if there's nothing wrong with the rotor or the carbon button in the distributor cap, I suppose the wires are just shot.

 

I just brought it up because usually when wires fail that way (arcing out the side), there is some other root cause, like either the insulation was burned from heat, damaged from oil, or the voltage was unexpectedly high.

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  • 3 weeks later...

There was resistance from the distributor cap to the wires. I cleaned the contacts and put some dielectric grease where the wires connected. That reduced the ohms. Now the resistance is fairly low. I ended up pulling the fuse on the starter to test drive it. It has a new condenser. I can see that sometimes there is some arching behind the starter button. I think that it is making contact with the block. Currently the car will not charge nor stop. I’ve given up on the brakes. The pedal goes to the floor and the car doesn’t slow down.  If I tighten it to where the pedal travel is good I can not get the wheels to move. I went around the block and I did not touch the brakes and they are smoking. I then let them cool and I was on a slight hill using the service and hand brake I could not prevent the car from rolling.   

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As for the brakes, it may be that the external contracting band (that has the brake lining material) is insufficiently round and so it can be adjusted close to the drum without excessive rub.  If the internal (parking brake) brakes don't work, look closely for signs of an oil leak from the end of the axle.  If the internal brake shoes are contaminated with gear oil, they won't be very effective.

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The  brakes are dry. A few years ago they got soaked is oil. I replaced the felts. The transmission slowly pumps oil into the differential. I have replaced the gasket and bearings but it still leaks. I just drain it a few times a year. I full the transmission to compensate. 

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I disconnected the generator while running and I can see that it is clearly producing voltage. The lead has 0 ohms to the frame. There is voltage between the battery and starter terminal on the starter button. For the time being I am ruling the starter generator out a faulty. I am looking into the wiring. The switch tests good in the bench. The starter and battery terminals test ♾  ohms. When connected to the leads there is 12v. I am getting somewhere slowly. 

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